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    //! String manipulation
    //!
    //! For more details, see std::str

    #![stable(feature = "rust1", since = "1.0.0")]

    use self::pattern::Pattern;
    use self::pattern::{Searcher, ReverseSearcher, DoubleEndedSearcher};

    use char;
    use fmt;
    use iter::{Map, Cloned, FusedIterator, TrustedLen, Filter};
    use iter_private::TrustedRandomAccess;
    use slice::{self, SliceIndex, Split as SliceSplit};
    use mem;

    pub mod pattern;

    #[unstable(feature = "str_internals", issue = "0")]
    #[allow(missing_docs)]
    pub mod lossy;

    /// Parse a value from a string
    ///
    /// `FromStr`'s [`from_str`] method is often used implicitly, through
    /// [`str`]'s [`parse`] method. See [`parse`]'s documentation for examples.
    ///
    /// [`from_str`]: #tymethod.from_str
    /// [`str`]: ../../std/primitive.str.html
    /// [`parse`]: ../../std/primitive.str.html#method.parse
    ///
    /// `FromStr` does not have a lifetime parameter, and so you can only parse types
    /// that do not contain a lifetime parameter themselves. In other words, you can
    /// parse an `i32` with `FromStr`, but not a `&i32`. You can parse a struct that
    /// contains an `i32`, but not one that contains an `&i32`.
    ///
    /// # Examples
    ///
    /// Basic implementation of `FromStr` on an example `Point` type:
    ///
    /// ```
    /// use std::str::FromStr;
    /// use std::num::ParseIntError;
    ///
    /// #[derive(Debug, PartialEq)]
    /// struct Point {
    ///     x: i32,
    ///     y: i32
    /// }
    ///
    /// impl FromStr for Point {
    ///     type Err = ParseIntError;
    ///
    ///     fn from_str(s: &str) -> Result<Self, Self::Err> {
    ///         let coords: Vec<&str> = s.trim_matches(|p| p == '(' || p == ')' )
    ///                                  .split(',')
    ///                                  .collect();
    ///
    ///         let x_fromstr = coords[0].parse::<i32>()?;
    ///         let y_fromstr = coords[1].parse::<i32>()?;
    ///
    ///         Ok(Point { x: x_fromstr, y: y_fromstr })
    ///     }
    /// }
    ///
    /// let p = Point::from_str("(1,2)");
    /// assert_eq!(p.unwrap(), Point{ x: 1, y: 2} )
    /// ```
    #[stable(feature = "rust1", since = "1.0.0")]
    pub trait FromStr: Sized {
        /// The associated error which can be returned from parsing.
        #[stable(feature = "rust1", since = "1.0.0")]
        type Err;

        /// Parses a string `s` to return a value of this type.
        ///
        /// If parsing succeeds, return the value inside [`Ok`], otherwise
        /// when the string is ill-formatted return an error specific to the
        /// inside [`Err`]. The error type is specific to implementation of the trait.
        ///
        /// [`Ok`]: ../../std/result/enum.Result.html#variant.Ok
        /// [`Err`]: ../../std/result/enum.Result.html#variant.Err
        ///
        /// # Examples
        ///
        /// Basic usage with [`i32`][ithirtytwo], a type that implements `FromStr`:
        ///
        /// [ithirtytwo]: ../../std/primitive.i32.html
        ///
        /// ```
        /// use std::str::FromStr;
        ///
        /// let s = "5";
        /// let x = i32::from_str(s).unwrap();
        ///
        /// assert_eq!(5, x);
        /// ```
        #[stable(feature = "rust1", since = "1.0.0")]
        fn from_str(s: &str) -> Result<Self, Self::Err>;
    }

    #[stable(feature = "rust1", since = "1.0.0")]
    impl FromStr for bool {
        type Err = ParseBoolError;

        /// Parse a `bool` from a string.
        ///
        /// Yields a `Result<bool, ParseBoolError>`, because `s` may or may not
        /// actually be parseable.
        ///
        /// # Examples
        ///
        /// ```
        /// use std::str::FromStr;
        ///
        /// assert_eq!(FromStr::from_str("true"), Ok(true));
        /// assert_eq!(FromStr::from_str("false"), Ok(false));
        /// assert!(<bool as FromStr>::from_str("not even a boolean").is_err());
        /// ```
        ///
        /// Note, in many cases, the `.parse()` method on `str` is more proper.
        ///
        /// ```
        /// assert_eq!("true".parse(), Ok(true));
        /// assert_eq!("false".parse(), Ok(false));
        /// assert!("not even a boolean".parse::<bool>().is_err());
        /// ```
        #[inline]
        fn from_str(s: &str) -> Result<bool, ParseBoolError> {
            match s {
                "true"  => Ok(true),
                "false" => Ok(false),
                _       => Err(ParseBoolError { _priv: () }),
            }
        }
    }

    /// An error returned when parsing a `bool` using [`from_str`] fails
    ///
    /// [`from_str`]: ../../std/primitive.bool.html#method.from_str
    #[derive(Debug, Clone, PartialEq, Eq)]
    #[stable(feature = "rust1", since = "1.0.0")]
    pub struct ParseBoolError { _priv: () }

    #[stable(feature = "rust1", since = "1.0.0")]
    impl fmt::Display for ParseBoolError {
        fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
            "provided string was not `true` or `false`".fmt(f)
        }
    }

    /*
    Section: Creating a string
    */

    /// Errors which can occur when attempting to interpret a sequence of [`u8`]
    /// as a string.
    ///
    /// [`u8`]: ../../std/primitive.u8.html
    ///
    /// As such, the `from_utf8` family of functions and methods for both [`String`]s
    /// and [`&str`]s make use of this error, for example.
    ///
    /// [`String`]: ../../std/string/struct.String.html#method.from_utf8
    /// [`&str`]: ../../std/str/fn.from_utf8.html
    ///
    /// # Examples
    ///
    /// This error type’s methods can be used to create functionality
    /// similar to `String::from_utf8_lossy` without allocating heap memory:
    ///
    /// ```
    /// fn from_utf8_lossy<F>(mut input: &[u8], mut push: F) where F: FnMut(&str) {
    ///     loop {
    ///         match ::std::str::from_utf8(input) {
    ///             Ok(valid) => {
    ///                 push(valid);
    ///                 break
    ///             }
    ///             Err(error) => {
    ///                 let (valid, after_valid) = input.split_at(error.valid_up_to());
    ///                 unsafe {
    ///                     push(::std::str::from_utf8_unchecked(valid))
    ///                 }
    ///                 push("\u{FFFD}");
    ///
    ///                 if let Some(invalid_sequence_length) = error.error_len() {
    ///                     input = &after_valid[invalid_sequence_length..]
    ///                 } else {
    ///                     break
    ///                 }
    ///             }
    ///         }
    ///     }
    /// }
    /// ```
    #[derive(Copy, Eq, PartialEq, Clone, Debug)]
    #[stable(feature = "rust1", since = "1.0.0")]
    pub struct Utf8Error {
        valid_up_to: usize,
        error_len: Option<u8>,
    }

    impl Utf8Error {
        /// Returns the index in the given string up to which valid UTF-8 was
        /// verified.
        ///
        /// It is the maximum index such that `from_utf8(&input[..index])`
        /// would return `Ok(_)`.
        ///
        /// # Examples
        ///
        /// Basic usage:
        ///
        /// ```
        /// use std::str;
        ///
        /// // some invalid bytes, in a vector
        /// let sparkle_heart = vec![0, 159, 146, 150];
        ///
        /// // std::str::from_utf8 returns a Utf8Error
        /// let error = str::from_utf8(&sparkle_heart).unwrap_err();
        ///
        /// // the second byte is invalid here
        /// assert_eq!(1, error.valid_up_to());
        /// ```
        #[stable(feature = "utf8_error", since = "1.5.0")]
        pub fn valid_up_to(&self) -> usize { self.valid_up_to }

        /// Provide more information about the failure:
        ///
        /// * `None`: the end of the input was reached unexpectedly.
        ///   `self.valid_up_to()` is 1 to 3 bytes from the end of the input.
        ///   If a byte stream (such as a file or a network socket) is being decoded incrementally,
        ///   this could be a valid `char` whose UTF-8 byte sequence is spanning multiple chunks.
        ///
        /// * `Some(len)`: an unexpected byte was encountered.
        ///   The length provided is that of the invalid byte sequence
        ///   that starts at the index given by `valid_up_to()`.
        ///   Decoding should resume after that sequence
        ///   (after inserting a [`U+FFFD REPLACEMENT CHARACTER`][U+FFFD]) in case of
        ///   lossy decoding.
        ///
        /// [U+FFFD]: ../../std/char/constant.REPLACEMENT_CHARACTER.html
        #[stable(feature = "utf8_error_error_len", since = "1.20.0")]
        pub fn error_len(&self) -> Option<usize> {
            self.error_len.map(|len| len as usize)
        }
    }

    /// Converts a slice of bytes to a string slice.
    ///
    /// A string slice ([`&str`]) is made of bytes ([`u8`]), and a byte slice
    /// ([`&[u8]`][byteslice]) is made of bytes, so this function converts between
    /// the two. Not all byte slices are valid string slices, however: [`&str`] requires
    /// that it is valid UTF-8. `from_utf8()` checks to ensure that the bytes are valid
    /// UTF-8, and then does the conversion.
    ///
    /// [`&str`]: ../../std/primitive.str.html
    /// [`u8`]: ../../std/primitive.u8.html
    /// [byteslice]: ../../std/primitive.slice.html
    ///
    /// If you are sure that the byte slice is valid UTF-8, and you don't want to
    /// incur the overhead of the validity check, there is an unsafe version of
    /// this function, [`from_utf8_unchecked`][fromutf8u], which has the same
    /// behavior but skips the check.
    ///
    /// [fromutf8u]: fn.from_utf8_unchecked.html
    ///
    /// If you need a `String` instead of a `&str`, consider
    /// [`String::from_utf8`][string].
    ///
    /// [string]: ../../std/string/struct.String.html#method.from_utf8
    ///
    /// Because you can stack-allocate a `[u8; N]`, and you can take a
    /// [`&[u8]`][byteslice] of it, this function is one way to have a
    /// stack-allocated string. There is an example of this in the
    /// examples section below.
    ///
    /// [byteslice]: ../../std/primitive.slice.html
    ///
    /// # Errors
    ///
    /// Returns `Err` if the slice is not UTF-8 with a description as to why the
    /// provided slice is not UTF-8.
    ///
    /// # Examples
    ///
    /// Basic usage:
    ///
    /// ```
    /// use std::str;
    ///
    /// // some bytes, in a vector
    /// let sparkle_heart = vec![240, 159, 146, 150];
    ///
    /// // We know these bytes are valid, so just use `unwrap()`.
    /// let sparkle_heart = str::from_utf8(&sparkle_heart).unwrap();
    ///
    /// assert_eq!("💖", sparkle_heart);
    /// ```
    ///
    /// Incorrect bytes:
    ///
    /// ```
    /// use std::str;
    ///
    /// // some invalid bytes, in a vector
    /// let sparkle_heart = vec![0, 159, 146, 150];
    ///
    /// assert!(str::from_utf8(&sparkle_heart).is_err());
    /// ```
    ///
    /// See the docs for [`Utf8Error`][error] for more details on the kinds of
    /// errors that can be returned.
    ///
    /// [error]: struct.Utf8Error.html
    ///
    /// A "stack allocated string":
    ///
    /// ```
    /// use std::str;
    ///
    /// // some bytes, in a stack-allocated array
    /// let sparkle_heart = [240, 159, 146, 150];
    ///
    /// // We know these bytes are valid, so just use `unwrap()`.
    /// let sparkle_heart = str::from_utf8(&sparkle_heart).unwrap();
    ///
    /// assert_eq!("💖", sparkle_heart);
    /// ```
    #[stable(feature = "rust1", since = "1.0.0")]
    pub fn from_utf8(v: &[u8]) -> Result<&str, Utf8Error> {
        run_utf8_validation(v)?;
        Ok(unsafe { from_utf8_unchecked(v) })
    }

    /// Converts a mutable slice of bytes to a mutable string slice.
    ///
    /// # Examples
    ///
    /// Basic usage:
    ///
    /// ```
    /// use std::str;
    ///
    /// // "Hello, Rust!" as a mutable vector
    /// let mut hellorust = vec![72, 101, 108, 108, 111, 44, 32, 82, 117, 115, 116, 33];
    ///
    /// // As we know these bytes are valid, we can use `unwrap()`
    /// let outstr = str::from_utf8_mut(&mut hellorust).unwrap();
    ///
    /// assert_eq!("Hello, Rust!", outstr);
    /// ```
    ///
    /// Incorrect bytes:
    ///
    /// ```
    /// use std::str;
    ///
    /// // Some invalid bytes in a mutable vector
    /// let mut invalid = vec![128, 223];
    ///
    /// assert!(str::from_utf8_mut(&mut invalid).is_err());
    /// ```
    /// See the docs for [`Utf8Error`][error] for more details on the kinds of
    /// errors that can be returned.
    ///
    /// [error]: struct.Utf8Error.html
    #[stable(feature = "str_mut_extras", since = "1.20.0")]
    pub fn from_utf8_mut(v: &mut [u8]) -> Result<&mut str, Utf8Error> {
        run_utf8_validation(v)?;
        Ok(unsafe { from_utf8_unchecked_mut(v) })
    }

    /// Converts a slice of bytes to a string slice without checking
    /// that the string contains valid UTF-8.
    ///
    /// See the safe version, [`from_utf8`][fromutf8], for more information.
    ///
    /// [fromutf8]: fn.from_utf8.html
    ///
    /// # Safety
    ///
    /// This function is unsafe because it does not check that the bytes passed to
    /// it are valid UTF-8. If this constraint is violated, undefined behavior
    /// results, as the rest of Rust assumes that [`&str`]s are valid UTF-8.
    ///
    /// [`&str`]: ../../std/primitive.str.html
    ///
    /// # Examples
    ///
    /// Basic usage:
    ///
    /// ```
    /// use std::str;
    ///
    /// // some bytes, in a vector
    /// let sparkle_heart = vec![240, 159, 146, 150];
    ///
    /// let sparkle_heart = unsafe {
    ///     str::from_utf8_unchecked(&sparkle_heart)
    /// };
    ///
    /// assert_eq!("💖", sparkle_heart);
    /// ```
    #[inline]
    #[stable(feature = "rust1", since = "1.0.0")]
    pub unsafe fn from_utf8_unchecked(v: &[u8]) -> &str {
        &*(v as *const [u8] as *const str)
    }

    /// Converts a slice of bytes to a string slice without checking
    /// that the string contains valid UTF-8; mutable version.
    ///
    /// See the immutable version, [`from_utf8_unchecked()`][fromutf8], for more information.
    ///
    /// [fromutf8]: fn.from_utf8_unchecked.html
    ///
    /// # Examples
    ///
    /// Basic usage:
    ///
    /// ```
    /// use std::str;
    ///
    /// let mut heart = vec![240, 159, 146, 150];
    /// let heart = unsafe { str::from_utf8_unchecked_mut(&mut heart) };
    ///
    /// assert_eq!("💖", heart);
    /// ```
    #[inline]
    #[stable(feature = "str_mut_extras", since = "1.20.0")]
    pub unsafe fn from_utf8_unchecked_mut(v: &mut [u8]) -> &mut str {
        &mut *(v as *mut [u8] as *mut str)
    }

    #[stable(feature = "rust1", since = "1.0.0")]
    impl fmt::Display for Utf8Error {
        fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
            if let Some(error_len) = self.error_len {
                write!(f, "invalid utf-8 sequence of {} bytes from index {}",
                       error_len, self.valid_up_to)
            } else {
                write!(f, "incomplete utf-8 byte sequence from index {}", self.valid_up_to)
            }
        }
    }

    /*
    Section: Iterators
    */

    /// An iterator over the [`char`]s of a string slice.
    ///
    /// [`char`]: ../../std/primitive.char.html
    ///
    /// This struct is created by the [`chars`] method on [`str`].
    /// See its documentation for more.
    ///
    /// [`chars`]: ../../std/primitive.str.html#method.chars
    /// [`str`]: ../../std/primitive.str.html
    #[derive(Clone, Debug)]
    #[stable(feature = "rust1", since = "1.0.0")]
    pub struct Chars<'a> {
        iter: slice::Iter<'a, u8>
    }

    /// Returns the initial codepoint accumulator for the first byte.
    /// The first byte is special, only want bottom 5 bits for width 2, 4 bits
    /// for width 3, and 3 bits for width 4.
    #[inline]
    fn utf8_first_byte(byte: u8, width: u32) -> u32 { (byte & (0x7F >> width)) as u32 }

    /// Returns the value of `ch` updated with continuation byte `byte`.
    #[inline]
    fn utf8_acc_cont_byte(ch: u32, byte: u8) -> u32 { (ch << 6) | (byte & CONT_MASK) as u32 }

    /// Checks whether the byte is a UTF-8 continuation byte (i.e., starts with the
    /// bits `10`).
    #[inline]
    fn utf8_is_cont_byte(byte: u8) -> bool { (byte & !CONT_MASK) == TAG_CONT_U8 }

    #[inline]
    fn unwrap_or_0(opt: Option<&u8>) -> u8 {
        match opt {
            Some(&byte) => byte,
            None => 0,
        }
    }

    /// Reads the next code point out of a byte iterator (assuming a
    /// UTF-8-like encoding).
    #[unstable(feature = "str_internals", issue = "0")]
    #[inline]
    pub fn next_code_point<'a, I: Iterator<Item = &'a u8>>(bytes: &mut I) -> Option<u32> {
        // Decode UTF-8
        let x = *bytes.next()?;
        if x < 128 {
            return Some(x as u32)
        }

        // Multibyte case follows
        // Decode from a byte combination out of: [[[x y] z] w]
        // NOTE: Performance is sensitive to the exact formulation here
        let init = utf8_first_byte(x, 2);
        let y = unwrap_or_0(bytes.next());
        let mut ch = utf8_acc_cont_byte(init, y);
        if x >= 0xE0 {
            // [[x y z] w] case
            // 5th bit in 0xE0 .. 0xEF is always clear, so `init` is still valid
            let z = unwrap_or_0(bytes.next());
            let y_z = utf8_acc_cont_byte((y & CONT_MASK) as u32, z);
            ch = init << 12 | y_z;
            if x >= 0xF0 {
                // [x y z w] case
                // use only the lower 3 bits of `init`
                let w = unwrap_or_0(bytes.next());
                ch = (init & 7) << 18 | utf8_acc_cont_byte(y_z, w);
            }
        }

        Some(ch)
    }

    /// Reads the last code point out of a byte iterator (assuming a
    /// UTF-8-like encoding).
    #[inline]
    fn next_code_point_reverse<'a, I>(bytes: &mut I) -> Option<u32>
        where I: DoubleEndedIterator<Item = &'a u8>,
    {
        // Decode UTF-8
        let w = match *bytes.next_back()? {
            next_byte if next_byte < 128 => return Some(next_byte as u32),
            back_byte => back_byte,
        };

        // Multibyte case follows
        // Decode from a byte combination out of: [x [y [z w]]]
        let mut ch;
        let z = unwrap_or_0(bytes.next_back());
        ch = utf8_first_byte(z, 2);
        if utf8_is_cont_byte(z) {
            let y = unwrap_or_0(bytes.next_back());
            ch = utf8_first_byte(y, 3);
            if utf8_is_cont_byte(y) {
                let x = unwrap_or_0(bytes.next_back());
                ch = utf8_first_byte(x, 4);
                ch = utf8_acc_cont_byte(ch, y);
            }
            ch = utf8_acc_cont_byte(ch, z);
        }
        ch = utf8_acc_cont_byte(ch, w);

        Some(ch)
    }

    #[stable(feature = "rust1", since = "1.0.0")]
    impl<'a> Iterator for Chars<'a> {
        type Item = char;

        #[inline]
        fn next(&mut self) -> Option<char> {
            next_code_point(&mut self.iter).map(|ch| {
                // str invariant says `ch` is a valid Unicode Scalar Value
                unsafe {
                    char::from_u32_unchecked(ch)
                }
            })
        }

        #[inline]
        fn count(self) -> usize {
            // length in `char` is equal to the number of non-continuation bytes
            let bytes_len = self.iter.len();
            let mut cont_bytes = 0;
            for &byte in self.iter {
                cont_bytes += utf8_is_cont_byte(byte) as usize;
            }
            bytes_len - cont_bytes
        }

        #[inline]
        fn size_hint(&self) -> (usize, Option<usize>) {
            let len = self.iter.len();
            // `(len + 3)` can't overflow, because we know that the `slice::Iter`
            // belongs to a slice in memory which has a maximum length of
            // `isize::MAX` (that's well below `usize::MAX`).
            ((len + 3) / 4, Some(len))
        }

        #[inline]
        fn last(mut self) -> Option<char> {
            // No need to go through the entire string.
            self.next_back()
        }
    }

    #[stable(feature = "rust1", since = "1.0.0")]
    impl<'a> DoubleEndedIterator for Chars<'a> {
        #[inline]
        fn next_back(&mut self) -> Option<char> {
            next_code_point_reverse(&mut self.iter).map(|ch| {
                // str invariant says `ch` is a valid Unicode Scalar Value
                unsafe {
                    char::from_u32_unchecked(ch)
                }
            })
        }
    }

    #[stable(feature = "fused", since = "1.26.0")]
    impl FusedIterator for Chars<'_> {}

    impl<'a> Chars<'a> {
        /// View the underlying data as a subslice of the original data.
        ///
        /// This has the same lifetime as the original slice, and so the
        /// iterator can continue to be used while this exists.
        ///
        /// # Examples
        ///
        /// ```
        /// let mut chars = "abc".chars();
        ///
        /// assert_eq!(chars.as_str(), "abc");
        /// chars.next();
        /// assert_eq!(chars.as_str(), "bc");
        /// chars.next();
        /// chars.next();
        /// assert_eq!(chars.as_str(), "");
        /// ```
        #[stable(feature = "iter_to_slice", since = "1.4.0")]
        #[inline]
        pub fn as_str(&self) -> &'a str {
            unsafe { from_utf8_unchecked(self.iter.as_slice()) }
        }
    }

    /// An iterator over the [`char`]s of a string slice, and their positions.
    ///
    /// [`char`]: ../../std/primitive.char.html
    ///
    /// This struct is created by the [`char_indices`] method on [`str`].
    /// See its documentation for more.
    ///
    /// [`char_indices`]: ../../std/primitive.str.html#method.char_indices
    /// [`str`]: ../../std/primitive.str.html
    #[derive(Clone, Debug)]
    #[stable(feature = "rust1", since = "1.0.0")]
    pub struct CharIndices<'a> {
        front_offset: usize,
        iter: Chars<'a>,
    }

    #[stable(feature = "rust1", since = "1.0.0")]
    impl<'a> Iterator for CharIndices<'a> {
        type Item = (usize, char);

        #[inline]
        fn next(&mut self) -> Option<(usize, char)> {
            let pre_len = self.iter.iter.len();
            match self.iter.next() {
                None => None,
                Some(ch) => {
                    let index = self.front_offset;
                    let len = self.iter.iter.len();
                    self.front_offset += pre_len - len;
                    Some((index, ch))
                }
            }
        }

        #[inline]
        fn count(self) -> usize {
            self.iter.count()
        }

        #[inline]
        fn size_hint(&self) -> (usize, Option<usize>) {
            self.iter.size_hint()
        }

        #[inline]
        fn last(mut self) -> Option<(usize, char)> {
            // No need to go through the entire string.
            self.next_back()
        }
    }

    #[stable(feature = "rust1", since = "1.0.0")]
    impl<'a> DoubleEndedIterator for CharIndices<'a> {
        #[inline]
        fn next_back(&mut self) -> Option<(usize, char)> {
            self.iter.next_back().map(|ch| {
                let index = self.front_offset + self.iter.iter.len();
                (index, ch)
            })
        }
    }

    #[stable(feature = "fused", since = "1.26.0")]
    impl FusedIterator for CharIndices<'_> {}

    impl<'a> CharIndices<'a> {
        /// View the underlying data as a subslice of the original data.
        ///
        /// This has the same lifetime as the original slice, and so the
        /// iterator can continue to be used while this exists.
        #[stable(feature = "iter_to_slice", since = "1.4.0")]
        #[inline]
        pub fn as_str(&self) -> &'a str {
            self.iter.as_str()
        }
    }

    /// An iterator over the bytes of a string slice.
    ///
    /// This struct is created by the [`bytes`] method on [`str`].
    /// See its documentation for more.
    ///
    /// [`bytes`]: ../../std/primitive.str.html#method.bytes
    /// [`str`]: ../../std/primitive.str.html
    #[stable(feature = "rust1", since = "1.0.0")]
    #[derive(Clone, Debug)]
    pub struct Bytes<'a>(Cloned<slice::Iter<'a, u8>>);

    #[stable(feature = "rust1", since = "1.0.0")]
    impl Iterator for Bytes<'_> {
        type Item = u8;

        #[inline]
        fn next(&mut self) -> Option<u8> {
            self.0.next()
        }

        #[inline]
        fn size_hint(&self) -> (usize, Option<usize>) {
            self.0.size_hint()
        }

        #[inline]
        fn count(self) -> usize {
            self.0.count()
        }

        #[inline]
        fn last(self) -> Option<Self::Item> {
            self.0.last()
        }

        #[inline]
        fn nth(&mut self, n: usize) -> Option<Self::Item> {
            self.0.nth(n)
        }

        #[inline]
        fn all<F>(&mut self, f: F) -> bool where F: FnMut(Self::Item) -> bool {
            self.0.all(f)
        }

        #[inline]
        fn any<F>(&mut self, f: F) -> bool where F: FnMut(Self::Item) -> bool {
            self.0.any(f)
        }

        #[inline]
        fn find<P>(&mut self, predicate: P) -> Option<Self::Item> where
            P: FnMut(&Self::Item) -> bool
        {
            self.0.find(predicate)
        }

        #[inline]
        fn position<P>(&mut self, predicate: P) -> Option<usize> where
            P: FnMut(Self::Item) -> bool
        {
            self.0.position(predicate)
        }

        #[inline]
        fn rposition<P>(&mut self, predicate: P) -> Option<usize> where
            P: FnMut(Self::Item) -> bool
        {
            self.0.rposition(predicate)
        }
    }

    #[stable(feature = "rust1", since = "1.0.0")]
    impl DoubleEndedIterator for Bytes<'_> {
        #[inline]
        fn next_back(&mut self) -> Option<u8> {
            self.0.next_back()
        }

        #[inline]
        fn rfind<P>(&mut self, predicate: P) -> Option<Self::Item> where
            P: FnMut(&Self::Item) -> bool
        {
            self.0.rfind(predicate)
        }
    }

    #[stable(feature = "rust1", since = "1.0.0")]
    impl ExactSizeIterator for Bytes<'_> {
        #[inline]
        fn len(&self) -> usize {
            self.0.len()
        }

        #[inline]
        fn is_empty(&self) -> bool {
            self.0.is_empty()
        }
    }

    #[stable(feature = "fused", since = "1.26.0")]
    impl FusedIterator for Bytes<'_> {}

    #[unstable(feature = "trusted_len", issue = "37572")]
    unsafe impl TrustedLen for Bytes<'_> {}

    #[doc(hidden)]
    unsafe impl<'a> TrustedRandomAccess for Bytes<'a> {
        unsafe fn get_unchecked(&mut self, i: usize) -> u8 {
            self.0.get_unchecked(i)
        }
        fn may_have_side_effect() -> bool { false }
    }

    /// This macro generates a Clone impl for string pattern API
    /// wrapper types of the form X<'a, P>
    macro_rules! derive_pattern_clone {
        (clone $t:ident with |$s:ident| $e:expr) => {
            impl<'a, P: Pattern<'a>> Clone for $t<'a, P>
                where P::Searcher: Clone
            {
                fn clone(&self) -> Self {
                    let $s = self;
                    $e
                }
            }
        }
    }

    /// This macro generates two public iterator structs
    /// wrapping a private internal one that makes use of the `Pattern` API.
    ///
    /// For all patterns `P: Pattern<'a>` the following items will be
    /// generated (generics omitted):
    ///
    /// struct $forward_iterator($internal_iterator);
    /// struct $reverse_iterator($internal_iterator);
    ///
    /// impl Iterator for $forward_iterator
    /// { /* internal ends up calling Searcher::next_match() */ }
    ///
    /// impl DoubleEndedIterator for $forward_iterator
    ///       where P::Searcher: DoubleEndedSearcher
    /// { /* internal ends up calling Searcher::next_match_back() */ }
    ///
    /// impl Iterator for $reverse_iterator
    ///       where P::Searcher: ReverseSearcher
    /// { /* internal ends up calling Searcher::next_match_back() */ }
    ///
    /// impl DoubleEndedIterator for $reverse_iterator
    ///       where P::Searcher: DoubleEndedSearcher
    /// { /* internal ends up calling Searcher::next_match() */ }
    ///
    /// The internal one is defined outside the macro, and has almost the same
    /// semantic as a DoubleEndedIterator by delegating to `pattern::Searcher` and
    /// `pattern::ReverseSearcher` for both forward and reverse iteration.
    ///
    /// "Almost", because a `Searcher` and a `ReverseSearcher` for a given
    /// `Pattern` might not return the same elements, so actually implementing
    /// `DoubleEndedIterator` for it would be incorrect.
    /// (See the docs in `str::pattern` for more details)
    ///
    /// However, the internal struct still represents a single ended iterator from
    /// either end, and depending on pattern is also a valid double ended iterator,
    /// so the two wrapper structs implement `Iterator`
    /// and `DoubleEndedIterator` depending on the concrete pattern type, leading
    /// to the complex impls seen above.
    macro_rules! generate_pattern_iterators {
        {
            // Forward iterator
            forward:
                $(#[$forward_iterator_attribute:meta])*
                struct $forward_iterator:ident;

            // Reverse iterator
            reverse:
                $(#[$reverse_iterator_attribute:meta])*
                struct $reverse_iterator:ident;

            // Stability of all generated items
            stability:
                $(#[$common_stability_attribute:meta])*

            // Internal almost-iterator that is being delegated to
            internal:
                $internal_iterator:ident yielding ($iterty:ty);

            // Kind of delegation - either single ended or double ended
            delegate $($t:tt)*
        } => {
            $(#[$forward_iterator_attribute])*
            $(#[$common_stability_attribute])*
            pub struct $forward_iterator<'a, P: Pattern<'a>>($internal_iterator<'a, P>);

            $(#[$common_stability_attribute])*
            impl<'a, P: Pattern<'a>> fmt::Debug for $forward_iterator<'a, P>
                where P::Searcher: fmt::Debug
            {
                fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
                    f.debug_tuple(stringify!($forward_iterator))
                        .field(&self.0)
                        .finish()
                }
            }

            $(#[$common_stability_attribute])*
            impl<'a, P: Pattern<'a>> Iterator for $forward_iterator<'a, P> {
                type Item = $iterty;

                #[inline]
                fn next(&mut self) -> Option<$iterty> {
                    self.0.next()
                }
            }

            $(#[$common_stability_attribute])*
            impl<'a, P: Pattern<'a>> Clone for $forward_iterator<'a, P>
                where P::Searcher: Clone
            {
                fn clone(&self) -> Self {
                    $forward_iterator(self.0.clone())
                }
            }

            $(#[$reverse_iterator_attribute])*
            $(#[$common_stability_attribute])*
            pub struct $reverse_iterator<'a, P: Pattern<'a>>($internal_iterator<'a, P>);

            $(#[$common_stability_attribute])*
            impl<'a, P: Pattern<'a>> fmt::Debug for $reverse_iterator<'a, P>
                where P::Searcher: fmt::Debug
            {
                fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
                    f.debug_tuple(stringify!($reverse_iterator))
                        .field(&self.0)
                        .finish()
                }
            }

            $(#[$common_stability_attribute])*
            impl<'a, P: Pattern<'a>> Iterator for $reverse_iterator<'a, P>
                where P::Searcher: ReverseSearcher<'a>
            {
                type Item = $iterty;

                #[inline]
                fn next(&mut self) -> Option<$iterty> {
                    self.0.next_back()
                }
            }

            $(#[$common_stability_attribute])*
            impl<'a, P: Pattern<'a>> Clone for $reverse_iterator<'a, P>
                where P::Searcher: Clone
            {
                fn clone(&self) -> Self {
                    $reverse_iterator(self.0.clone())
                }
            }

            #[stable(feature = "fused", since = "1.26.0")]
            impl<'a, P: Pattern<'a>> FusedIterator for $forward_iterator<'a, P> {}

            #[stable(feature = "fused", since = "1.26.0")]
            impl<'a, P: Pattern<'a>> FusedIterator for $reverse_iterator<'a, P>
                where P::Searcher: ReverseSearcher<'a> {}

            generate_pattern_iterators!($($t)* with $(#[$common_stability_attribute])*,
                                                    $forward_iterator,
                                                    $reverse_iterator, $iterty);
        };
        {
            double ended; with $(#[$common_stability_attribute:meta])*,
                               $forward_iterator:ident,
                               $reverse_iterator:ident, $iterty:ty
        } => {
            $(#[$common_stability_attribute])*
            impl<'a, P: Pattern<'a>> DoubleEndedIterator for $forward_iterator<'a, P>
                where P::Searcher: DoubleEndedSearcher<'a>
            {
                #[inline]
                fn next_back(&mut self) -> Option<$iterty> {
                    self.0.next_back()
                }
            }

            $(#[$common_stability_attribute])*
            impl<'a, P: Pattern<'a>> DoubleEndedIterator for $reverse_iterator<'a, P>
                where P::Searcher: DoubleEndedSearcher<'a>
            {
                #[inline]
                fn next_back(&mut self) -> Option<$iterty> {
                    self.0.next()
                }
            }
        };
        {
            single ended; with $(#[$common_stability_attribute:meta])*,
                               $forward_iterator:ident,
                               $reverse_iterator:ident, $iterty:ty
        } => {}
    }

    derive_pattern_clone!{
        clone SplitInternal
        with |s| SplitInternal { matcher: s.matcher.clone(), ..*s }
    }

    struct SplitInternal<'a, P: Pattern<'a>> {
        start: usize,
        end: usize,
        matcher: P::Searcher,
        allow_trailing_empty: bool,
        finished: bool,
    }

    impl<'a, P: Pattern<'a>> fmt::Debug for SplitInternal<'a, P> where P::Searcher: fmt::Debug {
        fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
            f.debug_struct("SplitInternal")
                .field("start", &self.start)
                .field("end", &self.end)
                .field("matcher", &self.matcher)
                .field("allow_trailing_empty", &self.allow_trailing_empty)
                .field("finished", &self.finished)
                .finish()
        }
    }

    impl<'a, P: Pattern<'a>> SplitInternal<'a, P> {
        #[inline]
        fn get_end(&mut self) -> Option<&'a str> {
            if !self.finished && (self.allow_trailing_empty || self.end - self.start > 0) {
                self.finished = true;
                unsafe {
                    let string = self.matcher.haystack().get_unchecked(self.start..self.end);
                    Some(string)
                }
            } else {
                None
            }
        }

        #[inline]
        fn next(&mut self) -> Option<&'a str> {
            if self.finished { return None }

            let haystack = self.matcher.haystack();
            match self.matcher.next_match() {
                Some((a, b)) => unsafe {
                    let elt = haystack.get_unchecked(self.start..a);
                    self.start = b;
                    Some(elt)
                },
                None => self.get_end(),
            }
        }

        #[inline]
        fn next_back(&mut self) -> Option<&'a str>
            where P::Searcher: ReverseSearcher<'a>
        {
            if self.finished { return None }

            if !self.allow_trailing_empty {
                self.allow_trailing_empty = true;
                match self.next_back() {
                    Some(elt) if !elt.is_empty() => return Some(elt),
                    _ => if self.finished { return None }
                }
            }

            let haystack = self.matcher.haystack();
            match self.matcher.next_match_back() {
                Some((a, b)) => unsafe {
                    let elt = haystack.get_unchecked(b..self.end);
                    self.end = a;
                    Some(elt)
                },
                None => unsafe {
                    self.finished = true;
                    Some(haystack.get_unchecked(self.start..self.end))
                },
            }
        }
    }

    generate_pattern_iterators! {
        forward:
            /// Created with the method [`split`].
            ///
            /// [`split`]: ../../std/primitive.str.html#method.split
            struct Split;
        reverse:
            /// Created with the method [`rsplit`].
            ///
            /// [`rsplit`]: ../../std/primitive.str.html#method.rsplit
            struct RSplit;
        stability:
            #[stable(feature = "rust1", since = "1.0.0")]
        internal:
            SplitInternal yielding (&'a str);
        delegate double ended;
    }

    generate_pattern_iterators! {
        forward:
            /// Created with the method [`split_terminator`].
            ///
            /// [`split_terminator`]: ../../std/primitive.str.html#method.split_terminator
            struct SplitTerminator;
        reverse:
            /// Created with the method [`rsplit_terminator`].
            ///
            /// [`rsplit_terminator`]: ../../std/primitive.str.html#method.rsplit_terminator
            struct RSplitTerminator;
        stability:
            #[stable(feature = "rust1", since = "1.0.0")]
        internal:
            SplitInternal yielding (&'a str);
        delegate double ended;
    }

    derive_pattern_clone!{
        clone SplitNInternal
        with |s| SplitNInternal { iter: s.iter.clone(), ..*s }
    }

    struct SplitNInternal<'a, P: Pattern<'a>> {
        iter: SplitInternal<'a, P>,
        /// The number of splits remaining
        count: usize,
    }

    impl<'a, P: Pattern<'a>> fmt::Debug for SplitNInternal<'a, P> where P::Searcher: fmt::Debug {
        fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
            f.debug_struct("SplitNInternal")
                .field("iter", &self.iter)
                .field("count", &self.count)
                .finish()
        }
    }

    impl<'a, P: Pattern<'a>> SplitNInternal<'a, P> {
        #[inline]
        fn next(&mut self) -> Option<&'a str> {
            match self.count {
                0 => None,
                1 => { self.count = 0; self.iter.get_end() }
                _ => { self.count -= 1; self.iter.next() }
            }
        }

        #[inline]
        fn next_back(&mut self) -> Option<&'a str>
            where P::Searcher: ReverseSearcher<'a>
        {
            match self.count {
                0 => None,
                1 => { self.count = 0; self.iter.get_end() }
                _ => { self.count -= 1; self.iter.next_back() }
            }
        }
    }

    generate_pattern_iterators! {
        forward:
            /// Created with the method [`splitn`].
            ///
            /// [`splitn`]: ../../std/primitive.str.html#method.splitn
            struct SplitN;
        reverse:
            /// Created with the method [`rsplitn`].
            ///
            /// [`rsplitn`]: ../../std/primitive.str.html#method.rsplitn
            struct RSplitN;
        stability:
            #[stable(feature = "rust1", since = "1.0.0")]
        internal:
            SplitNInternal yielding (&'a str);
        delegate single ended;
    }

    derive_pattern_clone!{
        clone MatchIndicesInternal
        with |s| MatchIndicesInternal(s.0.clone())
    }

    struct MatchIndicesInternal<'a, P: Pattern<'a>>(P::Searcher);

    impl<'a, P: Pattern<'a>> fmt::Debug for MatchIndicesInternal<'a, P> where P::Searcher: fmt::Debug {
        fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
            f.debug_tuple("MatchIndicesInternal")
                .field(&self.0)
                .finish()
        }
    }

    impl<'a, P: Pattern<'a>> MatchIndicesInternal<'a, P> {
        #[inline]
        fn next(&mut self) -> Option<(usize, &'a str)> {
            self.0.next_match().map(|(start, end)| unsafe {
                (start, self.0.haystack().get_unchecked(start..end))
            })
        }

        #[inline]
        fn next_back(&mut self) -> Option<(usize, &'a str)>
            where P::Searcher: ReverseSearcher<'a>
        {
            self.0.next_match_back().map(|(start, end)| unsafe {
                (start, self.0.haystack().get_unchecked(start..end))
            })
        }
    }

    generate_pattern_iterators! {
        forward:
            /// Created with the method [`match_indices`].
            ///
            /// [`match_indices`]: ../../std/primitive.str.html#method.match_indices
            struct MatchIndices;
        reverse:
            /// Created with the method [`rmatch_indices`].
            ///
            /// [`rmatch_indices`]: ../../std/primitive.str.html#method.rmatch_indices
            struct RMatchIndices;
        stability:
            #[stable(feature = "str_match_indices", since = "1.5.0")]
        internal:
            MatchIndicesInternal yielding ((usize, &'a str));
        delegate double ended;
    }

    derive_pattern_clone!{
        clone MatchesInternal
        with |s| MatchesInternal(s.0.clone())
    }

    struct MatchesInternal<'a, P: Pattern<'a>>(P::Searcher);

    impl<'a, P: Pattern<'a>> fmt::Debug for MatchesInternal<'a, P> where P::Searcher: fmt::Debug {
        fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
            f.debug_tuple("MatchesInternal")
                .field(&self.0)
                .finish()
        }
    }

    impl<'a, P: Pattern<'a>> MatchesInternal<'a, P> {
        #[inline]
        fn next(&mut self) -> Option<&'a str> {
            self.0.next_match().map(|(a, b)| unsafe {
                // Indices are known to be on utf8 boundaries
                self.0.haystack().get_unchecked(a..b)
            })
        }

        #[inline]
        fn next_back(&mut self) -> Option<&'a str>
            where P::Searcher: ReverseSearcher<'a>
        {
            self.0.next_match_back().map(|(a, b)| unsafe {
                // Indices are known to be on utf8 boundaries
                self.0.haystack().get_unchecked(a..b)
            })
        }
    }

    generate_pattern_iterators! {
        forward:
            /// Created with the method [`matches`].
            ///
            /// [`matches`]: ../../std/primitive.str.html#method.matches
            struct Matches;
        reverse:
            /// Created with the method [`rmatches`].
            ///
            /// [`rmatches`]: ../../std/primitive.str.html#method.rmatches
            struct RMatches;
        stability:
            #[stable(feature = "str_matches", since = "1.2.0")]
        internal:
            MatchesInternal yielding (&'a str);
        delegate double ended;
    }

    /// An iterator over the lines of a string, as string slices.
    ///
    /// This struct is created with the [`lines`] method on [`str`].
    /// See its documentation for more.
    ///
    /// [`lines`]: ../../std/primitive.str.html#method.lines
    /// [`str`]: ../../std/primitive.str.html
    #[stable(feature = "rust1", since = "1.0.0")]
    #[derive(Clone, Debug)]
    pub struct Lines<'a>(Map<SplitTerminator<'a, char>, LinesAnyMap>);

    #[stable(feature = "rust1", since = "1.0.0")]
    impl<'a> Iterator for Lines<'a> {
        type Item = &'a str;

        #[inline]
        fn next(&mut self) -> Option<&'a str> {
            self.0.next()
        }

        #[inline]
        fn size_hint(&self) -> (usize, Option<usize>) {
            self.0.size_hint()
        }
    }

    #[stable(feature = "rust1", since = "1.0.0")]
    impl<'a> DoubleEndedIterator for Lines<'a> {
        #[inline]
        fn next_back(&mut self) -> Option<&'a str> {
            self.0.next_back()
        }
    }

    #[stable(feature = "fused", since = "1.26.0")]
    impl FusedIterator for Lines<'_> {}

    /// Created with the method [`lines_any`].
    ///
    /// [`lines_any`]: ../../std/primitive.str.html#method.lines_any
    #[stable(feature = "rust1", since = "1.0.0")]
    #[rustc_deprecated(since = "1.4.0", reason = "use lines()/Lines instead now")]
    #[derive(Clone, Debug)]
    #[allow(deprecated)]
    pub struct LinesAny<'a>(Lines<'a>);

    /// A nameable, cloneable fn type
    #[derive(Clone)]
    struct LinesAnyMap;

    impl<'a> Fn<(&'a str,)> for LinesAnyMap {
        #[inline]
        extern "rust-call" fn call(&self, (line,): (&'a str,)) -> &'a str {
            let l = line.len();
            if l > 0 && line.as_bytes()[l - 1] == b'\r' { &line[0 .. l - 1] }
            else { line }
        }
    }

    impl<'a> FnMut<(&'a str,)> for LinesAnyMap {
        #[inline]
        extern "rust-call" fn call_mut(&mut self, (line,): (&'a str,)) -> &'a str {
            Fn::call(&*self, (line,))
        }
    }

    impl<'a> FnOnce<(&'a str,)> for LinesAnyMap {
        type Output = &'a str;

        #[inline]
        extern "rust-call" fn call_once(self, (line,): (&'a str,)) -> &'a str {
            Fn::call(&self, (line,))
        }
    }

    #[stable(feature = "rust1", since = "1.0.0")]
    #[allow(deprecated)]
    impl<'a> Iterator for LinesAny<'a> {
        type Item = &'a str;

        #[inline]
        fn next(&mut self) -> Option<&'a str> {
            self.0.next()
        }

        #[inline]
        fn size_hint(&self) -> (usize, Option<usize>) {
            self.0.size_hint()
        }
    }

    #[stable(feature = "rust1", since = "1.0.0")]
    #[allow(deprecated)]
    impl<'a> DoubleEndedIterator for LinesAny<'a> {
        #[inline]
        fn next_back(&mut self) -> Option<&'a str> {
            self.0.next_back()
        }
    }

    #[stable(feature = "fused", since = "1.26.0")]
    #[allow(deprecated)]
    impl FusedIterator for LinesAny<'_> {}

    /*
    Section: UTF-8 validation
    */

    // use truncation to fit u64 into usize
    const NONASCII_MASK: usize = 0x80808080_80808080u64 as usize;

    /// Returns `true` if any byte in the word `x` is nonascii (>= 128).
    #[inline]
    fn contains_nonascii(x: usize) -> bool {
        (x & NONASCII_MASK) != 0
    }

    /// Walks through `v` checking that it's a valid UTF-8 sequence,
    /// returning `Ok(())` in that case, or, if it is invalid, `Err(err)`.
    #[inline]
    fn run_utf8_validation(v: &[u8]) -> Result<(), Utf8Error> {
        let mut index = 0;
        let len = v.len();

        let usize_bytes = mem::size_of::<usize>();
        let ascii_block_size = 2 * usize_bytes;
        let blocks_end = if len >= ascii_block_size { len - ascii_block_size + 1 } else { 0 };

        while index < len {
            let old_offset = index;
            macro_rules! err {
                ($error_len: expr) => {
                    return Err(Utf8Error {
                        valid_up_to: old_offset,
                        error_len: $error_len,
                    })
                }
            }

            macro_rules! next { () => {{
                index += 1;
                // we needed data, but there was none: error!
                if index >= len {
                    err!(None)
                }
                v[index]
            }}}

            let first = v[index];
            if first >= 128 {
                let w = UTF8_CHAR_WIDTH[first as usize];
                // 2-byte encoding is for codepoints  \u{0080} to  \u{07ff}
                //        first  C2 80        last DF BF
                // 3-byte encoding is for codepoints  \u{0800} to  \u{ffff}
                //        first  E0 A0 80     last EF BF BF
                //   excluding surrogates codepoints  \u{d800} to  \u{dfff}
                //               ED A0 80 to       ED BF BF
                // 4-byte encoding is for codepoints \u{1000}0 to \u{10ff}ff
                //        first  F0 90 80 80  last F4 8F BF BF
                //
                // Use the UTF-8 syntax from the RFC
                //
                // https://tools.ietf.org/html/rfc3629
                // UTF8-1      = %x00-7F
                // UTF8-2      = %xC2-DF UTF8-tail
                // UTF8-3      = %xE0 %xA0-BF UTF8-tail / %xE1-EC 2( UTF8-tail ) /
                //               %xED %x80-9F UTF8-tail / %xEE-EF 2( UTF8-tail )
                // UTF8-4      = %xF0 %x90-BF 2( UTF8-tail ) / %xF1-F3 3( UTF8-tail ) /
                //               %xF4 %x80-8F 2( UTF8-tail )
                match w {
                    2 => if next!() & !CONT_MASK != TAG_CONT_U8 {
                        err!(Some(1))
                    },
                    3 => {
                        match (first, next!()) {
                            (0xE0         , 0xA0 ..= 0xBF) |
                            (0xE1 ..= 0xEC, 0x80 ..= 0xBF) |
                            (0xED         , 0x80 ..= 0x9F) |
                            (0xEE ..= 0xEF, 0x80 ..= 0xBF) => {}
                            _ => err!(Some(1))
                        }
                        if next!() & !CONT_MASK != TAG_CONT_U8 {
                            err!(Some(2))
                        }
                    }
                    4 => {
                        match (first, next!()) {
                            (0xF0         , 0x90 ..= 0xBF) |
                            (0xF1 ..= 0xF3, 0x80 ..= 0xBF) |
                            (0xF4         , 0x80 ..= 0x8F) => {}
                            _ => err!(Some(1))
                        }
                        if next!() & !CONT_MASK != TAG_CONT_U8 {
                            err!(Some(2))
                        }
                        if next!() & !CONT_MASK != TAG_CONT_U8 {
                            err!(Some(3))
                        }
                    }
                    _ => err!(Some(1))
                }
                index += 1;
            } else {
                // Ascii case, try to skip forward quickly.
                // When the pointer is aligned, read 2 words of data per iteration
                // until we find a word containing a non-ascii byte.
                let ptr = v.as_ptr();
                let align = unsafe {
                    // the offset is safe, because `index` is guaranteed inbounds
                    ptr.add(index).align_offset(usize_bytes)
                };
                if align == 0 {
                    while index < blocks_end {
                        unsafe {
                            let block = ptr.add(index) as *const usize;
                            // break if there is a nonascii byte
                            let zu = contains_nonascii(*block);
                            let zv = contains_nonascii(*block.offset(1));
                            if zu | zv {
                                break;
                            }
                        }
                        index += ascii_block_size;
                    }
                    // step from the point where the wordwise loop stopped
                    while index < len && v[index] < 128 {
                        index += 1;
                    }
                } else {
                    index += 1;
                }
            }
        }

        Ok(())
    }

    // https://tools.ietf.org/html/rfc3629
    static UTF8_CHAR_WIDTH: [u8; 256] = [
    1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,
    1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1, // 0x1F
    1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,
    1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1, // 0x3F
    1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,
    1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1, // 0x5F
    1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,
    1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1, // 0x7F
    0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
    0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, // 0x9F
    0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
    0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, // 0xBF
    0,0,2,2,2,2,2,2,2,2,2,2,2,2,2,2,
    2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2, // 0xDF
    3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3, // 0xEF
    4,4,4,4,4,0,0,0,0,0,0,0,0,0,0,0, // 0xFF
    ];

    /// Given a first byte, determines how many bytes are in this UTF-8 character.
    #[unstable(feature = "str_internals", issue = "0")]
    #[inline]
    pub fn utf8_char_width(b: u8) -> usize {
        UTF8_CHAR_WIDTH[b as usize] as usize
    }

    /// Mask of the value bits of a continuation byte.
    const CONT_MASK: u8 = 0b0011_1111;
    /// Value of the tag bits (tag mask is !CONT_MASK) of a continuation byte.
    const TAG_CONT_U8: u8 = 0b1000_0000;

    /*
    Section: Trait implementations
    */

    mod traits {
        use cmp::Ordering;
        use ops;
        use slice::{self, SliceIndex};

        /// Implements ordering of strings.
        ///
        /// Strings are ordered  lexicographically by their byte values.  This orders Unicode code
        /// points based on their positions in the code charts.  This is not necessarily the same as
        /// "alphabetical" order, which varies by language and locale.  Sorting strings according to
        /// culturally-accepted standards requires locale-specific data that is outside the scope of
        /// the `str` type.
        #[stable(feature = "rust1", since = "1.0.0")]
        impl Ord for str {
            #[inline]
            fn cmp(&self, other: &str) -> Ordering {
                self.as_bytes().cmp(other.as_bytes())
            }
        }

        #[stable(feature = "rust1", since = "1.0.0")]
        impl PartialEq for str {
            #[inline]
            fn eq(&self, other: &str) -> bool {
                self.as_bytes() == other.as_bytes()
            }
            #[inline]
            fn ne(&self, other: &str) -> bool { !(*self).eq(other) }
        }

        #[stable(feature = "rust1", since = "1.0.0")]
        impl Eq for str {}

        /// Implements comparison operations on strings.
        ///
        /// Strings are compared lexicographically by their byte values.  This compares Unicode code
        /// points based on their positions in the code charts.  This is not necessarily the same as
        /// "alphabetical" order, which varies by language and locale.  Comparing strings according to
        /// culturally-accepted standards requires locale-specific data that is outside the scope of
        /// the `str` type.
        #[stable(feature = "rust1", since = "1.0.0")]
        impl PartialOrd for str {
            #[inline]
            fn partial_cmp(&self, other: &str) -> Option<Ordering> {
                Some(self.cmp(other))
            }
        }

        /// Implements substring slicing with syntax `&self[begin .. end]`.
        ///
        /// Returns a slice of the given string from the byte range
        /// [`begin`..`end`).
        ///
        /// This operation is `O(1)`.
        ///
        /// # Panics
        ///
        /// Panics if `begin` or `end` does not point to the starting
        /// byte offset of a character (as defined by `is_char_boundary`).
        /// Requires that `begin <= end` and `end <= len` where `len` is the
        /// length of the string.
        ///
        /// # Examples
        ///
        /// ```
        /// let s = "Löwe 老虎 Léopard";
        /// assert_eq!(&s[0 .. 1], "L");
        ///
        /// assert_eq!(&s[1 .. 9], "öwe 老");
        ///
        /// // these will panic:
        /// // byte 2 lies within `ö`:
        /// // &s[2 ..3];
        ///
        /// // byte 8 lies within `老`
        /// // &s[1 .. 8];
        ///
        /// // byte 100 is outside the string
        /// // &s[3 .. 100];
        /// ```
        #[stable(feature = "rust1", since = "1.0.0")]
        impl ops::Index<ops::Range<usize>> for str {
            type Output = str;
            #[inline]
            fn index(&self, index: ops::Range<usize>) -> &str {
                index.index(self)
            }
        }

        /// Implements mutable substring slicing with syntax
        /// `&mut self[begin .. end]`.
        ///
        /// Returns a mutable slice of the given string from the byte range
        /// [`begin`..`end`).
        ///
        /// This operation is `O(1)`.
        ///
        /// # Panics
        ///
        /// Panics if `begin` or `end` does not point to the starting
        /// byte offset of a character (as defined by `is_char_boundary`).
        /// Requires that `begin <= end` and `end <= len` where `len` is the
        /// length of the string.
        #[stable(feature = "derefmut_for_string", since = "1.3.0")]
        impl ops::IndexMut<ops::Range<usize>> for str {
            #[inline]
            fn index_mut(&mut self, index: ops::Range<usize>) -> &mut str {
                index.index_mut(self)
            }
        }

        /// Implements substring slicing with syntax `&self[.. end]`.
        ///
        /// Returns a slice of the string from the beginning to byte offset
        /// `end`.
        ///
        /// Equivalent to `&self[0 .. end]`.
        #[stable(feature = "rust1", since = "1.0.0")]
        impl ops::Index<ops::RangeTo<usize>> for str {
            type Output = str;

            #[inline]
            fn index(&self, index: ops::RangeTo<usize>) -> &str {
                index.index(self)
            }
        }

        /// Implements mutable substring slicing with syntax `&mut self[.. end]`.
        ///
        /// Returns a mutable slice of the string from the beginning to byte offset
        /// `end`.
        ///
        /// Equivalent to `&mut self[0 .. end]`.
        #[stable(feature = "derefmut_for_string", since = "1.3.0")]
        impl ops::IndexMut<ops::RangeTo<usize>> for str {
            #[inline]
            fn index_mut(&mut self, index: ops::RangeTo<usize>) -> &mut str {
                index.index_mut(self)
            }
        }

        /// Implements substring slicing with syntax `&self[begin ..]`.
        ///
        /// Returns a slice of the string from byte offset `begin`
        /// to the end of the string.
        ///
        /// Equivalent to `&self[begin .. len]`.
        #[stable(feature = "rust1", since = "1.0.0")]
        impl ops::Index<ops::RangeFrom<usize>> for str {
            type Output = str;

            #[inline]
            fn index(&self, index: ops::RangeFrom<usize>) -> &str {
                index.index(self)
            }
        }

        /// Implements mutable substring slicing with syntax `&mut self[begin ..]`.
        ///
        /// Returns a mutable slice of the string from byte offset `begin`
        /// to the end of the string.
        ///
        /// Equivalent to `&mut self[begin .. len]`.
        #[stable(feature = "derefmut_for_string", since = "1.3.0")]
        impl ops::IndexMut<ops::RangeFrom<usize>> for str {
            #[inline]
            fn index_mut(&mut self, index: ops::RangeFrom<usize>) -> &mut str {
                index.index_mut(self)
            }
        }

        /// Implements substring slicing with syntax `&self[..]`.
        ///
        /// Returns a slice of the whole string. This operation can
        /// never panic.
        ///
        /// Equivalent to `&self[0 .. len]`.
        #[stable(feature = "rust1", since = "1.0.0")]
        impl ops::Index<ops::RangeFull> for str {
            type Output = str;

            #[inline]
            fn index(&self, _index: ops::RangeFull) -> &str {
                self
            }
        }

        /// Implements mutable substring slicing with syntax `&mut self[..]`.
        ///
        /// Returns a mutable slice of the whole string. This operation can
        /// never panic.
        ///
        /// Equivalent to `&mut self[0 .. len]`.
        #[stable(feature = "derefmut_for_string", since = "1.3.0")]
        impl ops::IndexMut<ops::RangeFull> for str {
            #[inline]
            fn index_mut(&mut self, _index: ops::RangeFull) -> &mut str {
                self
            }
        }

        #[stable(feature = "inclusive_range", since = "1.26.0")]
        impl ops::Index<ops::RangeInclusive<usize>> for str {
            type Output = str;

            #[inline]
            fn index(&self, index: ops::RangeInclusive<usize>) -> &str {
                index.index(self)
            }
        }

        #[stable(feature = "inclusive_range", since = "1.26.0")]
        impl ops::Index<ops::RangeToInclusive<usize>> for str {
            type Output = str;

            #[inline]
            fn index(&self, index: ops::RangeToInclusive<usize>) -> &str {
                index.index(self)
            }
        }

        #[stable(feature = "inclusive_range", since = "1.26.0")]
        impl ops::IndexMut<ops::RangeInclusive<usize>> for str {
            #[inline]
            fn index_mut(&mut self, index: ops::RangeInclusive<usize>) -> &mut str {
                index.index_mut(self)
            }
        }
        #[stable(feature = "inclusive_range", since = "1.26.0")]
        impl ops::IndexMut<ops::RangeToInclusive<usize>> for str {
            #[inline]
            fn index_mut(&mut self, index: ops::RangeToInclusive<usize>) -> &mut str {
                index.index_mut(self)
            }
        }

        #[inline(never)]
        #[cold]
        fn str_index_overflow_fail() -> ! {
            panic!("attempted to index str up to maximum usize");
        }

        #[stable(feature = "str_checked_slicing", since = "1.20.0")]
        impl SliceIndex<str> for ops::RangeFull {
            type Output = str;
            #[inline]
            fn get(self, slice: &str) -> Option<&Self::Output> {
                Some(slice)
            }
            #[inline]
            fn get_mut(self, slice: &mut str) -> Option<&mut Self::Output> {
                Some(slice)
            }
            #[inline]
            unsafe fn get_unchecked(self, slice: &str) -> &Self::Output {
                slice
            }
            #[inline]
            unsafe fn get_unchecked_mut(self, slice: &mut str) -> &mut Self::Output {
                slice
            }
            #[inline]
            fn index(self, slice: &str) -> &Self::Output {
                slice
            }
            #[inline]
            fn index_mut(self, slice: &mut str) -> &mut Self::Output {
                slice
            }
        }

        #[stable(feature = "str_checked_slicing", since = "1.20.0")]
        impl SliceIndex<str> for ops::Range<usize> {
            type Output = str;
            #[inline]
            fn get(self, slice: &str) -> Option<&Self::Output> {
                if self.start <= self.end &&
                   slice.is_char_boundary(self.start) &&
                   slice.is_char_boundary(self.end) {
                    Some(unsafe { self.get_unchecked(slice) })
                } else {
                    None
                }
            }
            #[inline]
            fn get_mut(self, slice: &mut str) -> Option<&mut Self::Output> {
                if self.start <= self.end &&
                   slice.is_char_boundary(self.start) &&
                   slice.is_char_boundary(self.end) {
                    Some(unsafe { self.get_unchecked_mut(slice) })
                } else {
                    None
                }
            }
            #[inline]
            unsafe fn get_unchecked(self, slice: &str) -> &Self::Output {
                let ptr = slice.as_ptr().add(self.start);
                let len = self.end - self.start;
                super::from_utf8_unchecked(slice::from_raw_parts(ptr, len))
            }
            #[inline]
            unsafe fn get_unchecked_mut(self, slice: &mut str) -> &mut Self::Output {
                let ptr = slice.as_ptr().add(self.start);
                let len = self.end - self.start;
                super::from_utf8_unchecked_mut(slice::from_raw_parts_mut(ptr as *mut u8, len))
            }
            #[inline]
            fn index(self, slice: &str) -> &Self::Output {
                let (start, end) = (self.start, self.end);
                self.get(slice).unwrap_or_else(|| super::slice_error_fail(slice, start, end))
            }
            #[inline]
            fn index_mut(self, slice: &mut str) -> &mut Self::Output {
                // is_char_boundary checks that the index is in [0, .len()]
                // cannot reuse `get` as above, because of NLL trouble
                if self.start <= self.end &&
                   slice.is_char_boundary(self.start) &&
                   slice.is_char_boundary(self.end) {
                    unsafe { self.get_unchecked_mut(slice) }
                } else {
                    super::slice_error_fail(slice, self.start, self.end)
                }
            }
        }

        #[stable(feature = "str_checked_slicing", since = "1.20.0")]
        impl SliceIndex<str> for ops::RangeTo<usize> {
            type Output = str;
            #[inline]
            fn get(self, slice: &str) -> Option<&Self::Output> {
                if slice.is_char_boundary(self.end) {
                    Some(unsafe { self.get_unchecked(slice) })
                } else {
                    None
                }
            }
            #[inline]
            fn get_mut(self, slice: &mut str) -> Option<&mut Self::Output> {
                if slice.is_char_boundary(self.end) {
                    Some(unsafe { self.get_unchecked_mut(slice) })
                } else {
                    None
                }
            }
            #[inline]
            unsafe fn get_unchecked(self, slice: &str) -> &Self::Output {
                let ptr = slice.as_ptr();
                super::from_utf8_unchecked(slice::from_raw_parts(ptr, self.end))
            }
            #[inline]
            unsafe fn get_unchecked_mut(self, slice: &mut str) -> &mut Self::Output {
                let ptr = slice.as_ptr();
                super::from_utf8_unchecked_mut(slice::from_raw_parts_mut(ptr as *mut u8, self.end))
            }
            #[inline]
            fn index(self, slice: &str) -> &Self::Output {
                let end = self.end;
                self.get(slice).unwrap_or_else(|| super::slice_error_fail(slice, 0, end))
            }
            #[inline]
            fn index_mut(self, slice: &mut str) -> &mut Self::Output {
                // is_char_boundary checks that the index is in [0, .len()]
                if slice.is_char_boundary(self.end) {
                    unsafe { self.get_unchecked_mut(slice) }
                } else {
                    super::slice_error_fail(slice, 0, self.end)
                }
            }
        }

        #[stable(feature = "str_checked_slicing", since = "1.20.0")]
        impl SliceIndex<str> for ops::RangeFrom<usize> {
            type Output = str;
            #[inline]
            fn get(self, slice: &str) -> Option<&Self::Output> {
                if slice.is_char_boundary(self.start) {
                    Some(unsafe { self.get_unchecked(slice) })
                } else {
                    None
                }
            }
            #[inline]
            fn get_mut(self, slice: &mut str) -> Option<&mut Self::Output> {
                if slice.is_char_boundary(self.start) {
                    Some(unsafe { self.get_unchecked_mut(slice) })
                } else {
                    None
                }
            }
            #[inline]
            unsafe fn get_unchecked(self, slice: &str) -> &Self::Output {
                let ptr = slice.as_ptr().add(self.start);
                let len = slice.len() - self.start;
                super::from_utf8_unchecked(slice::from_raw_parts(ptr, len))
            }
            #[inline]
            unsafe fn get_unchecked_mut(self, slice: &mut str) -> &mut Self::Output {
                let ptr = slice.as_ptr().add(self.start);
                let len = slice.len() - self.start;
                super::from_utf8_unchecked_mut(slice::from_raw_parts_mut(ptr as *mut u8, len))
            }
            #[inline]
            fn index(self, slice: &str) -> &Self::Output {
                let (start, end) = (self.start, slice.len());
                self.get(slice).unwrap_or_else(|| super::slice_error_fail(slice, start, end))
            }
            #[inline]
            fn index_mut(self, slice: &mut str) -> &mut Self::Output {
                // is_char_boundary checks that the index is in [0, .len()]
                if slice.is_char_boundary(self.start) {
                    unsafe { self.get_unchecked_mut(slice) }
                } else {
                    super::slice_error_fail(slice, self.start, slice.len())
                }
            }
        }

        #[stable(feature = "inclusive_range", since = "1.26.0")]
        impl SliceIndex<str> for ops::RangeInclusive<usize> {
            type Output = str;
            #[inline]
            fn get(self, slice: &str) -> Option<&Self::Output> {
                if *self.end() == usize::max_value() { None }
                else { (*self.start()..self.end()+1).get(slice) }
            }
            #[inline]
            fn get_mut(self, slice: &mut str) -> Option<&mut Self::Output> {
                if *self.end() == usize::max_value() { None }
                else { (*self.start()..self.end()+1).get_mut(slice) }
            }
            #[inline]
            unsafe fn get_unchecked(self, slice: &str) -> &Self::Output {
                (*self.start()..self.end()+1).get_unchecked(slice)
            }
            #[inline]
            unsafe fn get_unchecked_mut(self, slice: &mut str) -> &mut Self::Output {
                (*self.start()..self.end()+1).get_unchecked_mut(slice)
            }
            #[inline]
            fn index(self, slice: &str) -> &Self::Output {
                if *self.end() == usize::max_value() { str_index_overflow_fail(); }
                (*self.start()..self.end()+1).index(slice)
            }
            #[inline]
            fn index_mut(self, slice: &mut str) -> &mut Self::Output {
                if *self.end() == usize::max_value() { str_index_overflow_fail(); }
                (*self.start()..self.end()+1).index_mut(slice)
            }
        }

        #[stable(feature = "inclusive_range", since = "1.26.0")]
        impl SliceIndex<str> for ops::RangeToInclusive<usize> {
            type Output = str;
            #[inline]
            fn get(self, slice: &str) -> Option<&Self::Output> {
                if self.end == usize::max_value() { None }
                else { (..self.end+1).get(slice) }
            }
            #[inline]
            fn get_mut(self, slice: &mut str) -> Option<&mut Self::Output> {
                if self.end == usize::max_value() { None }
                else { (..self.end+1).get_mut(slice) }
            }
            #[inline]
            unsafe fn get_unchecked(self, slice: &str) -> &Self::Output {
                (..self.end+1).get_unchecked(slice)
            }
            #[inline]
            unsafe fn get_unchecked_mut(self, slice: &mut str) -> &mut Self::Output {
                (..self.end+1).get_unchecked_mut(slice)
            }
            #[inline]
            fn index(self, slice: &str) -> &Self::Output {
                if self.end == usize::max_value() { str_index_overflow_fail(); }
                (..self.end+1).index(slice)
            }
            #[inline]
            fn index_mut(self, slice: &mut str) -> &mut Self::Output {
                if self.end == usize::max_value() { str_index_overflow_fail(); }
                (..self.end+1).index_mut(slice)
            }
        }
    }

    // truncate `&str` to length at most equal to `max`
    // return `true` if it were truncated, and the new str.
    fn truncate_to_char_boundary(s: &str, mut max: usize) -> (bool, &str) {
        if max >= s.len() {
            (false, s)
        } else {
            while !s.is_char_boundary(max) {
                max -= 1;
            }
            (true, &s[..max])
        }
    }

    #[inline(never)]
    #[cold]
    fn slice_error_fail(s: &str, begin: usize, end: usize) -> ! {
        const MAX_DISPLAY_LENGTH: usize = 256;
        let (truncated, s_trunc) = truncate_to_char_boundary(s, MAX_DISPLAY_LENGTH);
        let ellipsis = if truncated { "[...]" } else { "" };

        // 1. out of bounds
        if begin > s.len() || end > s.len() {
            let oob_index = if begin > s.len() { begin } else { end };
            panic!("byte index {} is out of bounds of `{}`{}", oob_index, s_trunc, ellipsis);
        }

        // 2. begin <= end
        assert!(begin <= end, "begin <= end ({} <= {}) when slicing `{}`{}",
                begin, end, s_trunc, ellipsis);

        // 3. character boundary
        let index = if !s.is_char_boundary(begin) { begin } else { end };
        // find the character
        let mut char_start = index;
        while !s.is_char_boundary(char_start) {
            char_start -= 1;
        }
        // `char_start` must be less than len and a char boundary
        let ch = s[char_start..].chars().next().unwrap();
        let char_range = char_start .. char_start + ch.len_utf8();
        panic!("byte index {} is not a char boundary; it is inside {:?} (bytes {:?}) of `{}`{}",
               index, ch, char_range, s_trunc, ellipsis);
    }

    #[lang = "str"]
    #[cfg(not(test))]
    impl str {
        /// Returns the length of `self`.
        ///
        /// This length is in bytes, not [`char`]s or graphemes. In other words,
        /// it may not be what a human considers the length of the string.
        ///
        /// # Examples
        ///
        /// Basic usage:
        ///
        /// ```
        /// let len = "foo".len();
        /// assert_eq!(3, len);
        ///
        /// let len = "ƒoo".len(); // fancy f!
        /// assert_eq!(4, len);
        /// ```
        #[stable(feature = "rust1", since = "1.0.0")]
        #[inline]
        #[rustc_const_unstable(feature = "const_str_len")]
        pub const fn len(&self) -> usize {
            self.as_bytes().len()
        }

        /// Returns `true` if `self` has a length of zero bytes.
        ///
        /// # Examples
        ///
        /// Basic usage:
        ///
        /// ```
        /// let s = "";
        /// assert!(s.is_empty());
        ///
        /// let s = "not empty";
        /// assert!(!s.is_empty());
        /// ```
        #[inline]
        #[stable(feature = "rust1", since = "1.0.0")]
        #[rustc_const_unstable(feature = "const_str_len")]
        pub const fn is_empty(&self) -> bool {
            self.len() == 0
        }

        /// Checks that `index`-th byte lies at the start and/or end of a
        /// UTF-8 code point sequence.
        ///
        /// The start and end of the string (when `index == self.len()`) are
        /// considered to be
        /// boundaries.
        ///
        /// Returns `false` if `index` is greater than `self.len()`.
        ///
        /// # Examples
        ///
        /// ```
        /// let s = "Löwe 老虎 Léopard";
        /// assert!(s.is_char_boundary(0));
        /// // start of `老`
        /// assert!(s.is_char_boundary(6));
        /// assert!(s.is_char_boundary(s.len()));
        ///
        /// // second byte of `ö`
        /// assert!(!s.is_char_boundary(2));
        ///
        /// // third byte of `老`
        /// assert!(!s.is_char_boundary(8));
        /// ```
        #[stable(feature = "is_char_boundary", since = "1.9.0")]
        #[inline]
        pub fn is_char_boundary(&self, index: usize) -> bool {
            // 0 and len are always ok.
            // Test for 0 explicitly so that it can optimize out the check
            // easily and skip reading string data for that case.
            if index == 0 || index == self.len() { return true; }
            match self.as_bytes().get(index) {
                None => false,
                // This is bit magic equivalent to: b < 128 || b >= 192
                Some(&b) => (b as i8) >= -0x40,
            }
        }

        /// Converts a string slice to a byte slice. To convert the byte slice back
        /// into a string slice, use the [`str::from_utf8`] function.
        ///
        /// [`str::from_utf8`]: ./str/fn.from_utf8.html
        ///
        /// # Examples
        ///
        /// Basic usage:
        ///
        /// ```
        /// let bytes = "bors".as_bytes();
        /// assert_eq!(b"bors", bytes);
        /// ```
        #[stable(feature = "rust1", since = "1.0.0")]
        #[inline(always)]
        #[rustc_const_unstable(feature="const_str_as_bytes")]
        pub const fn as_bytes(&self) -> &[u8] {
            union Slices<'a> {
                str: &'a str,
                slice: &'a [u8],
            }
            unsafe { Slices { str: self }.slice }
        }

        /// Converts a mutable string slice to a mutable byte slice. To convert the
        /// mutable byte slice back into a mutable string slice, use the
        /// [`str::from_utf8_mut`] function.
        ///
        /// [`str::from_utf8_mut`]: ./str/fn.from_utf8_mut.html
        ///
        /// # Examples
        ///
        /// Basic usage:
        ///
        /// ```
        /// let mut s = String::from("Hello");
        /// let bytes = unsafe { s.as_bytes_mut() };
        ///
        /// assert_eq!(b"Hello", bytes);
        /// ```
        ///
        /// Mutability:
        ///
        /// ```
        /// let mut s = String::from("🗻∈🌏");
        ///
        /// unsafe {
        ///     let bytes = s.as_bytes_mut();
        ///
        ///     bytes[0] = 0xF0;
        ///     bytes[1] = 0x9F;
        ///     bytes[2] = 0x8D;
        ///     bytes[3] = 0x94;
        /// }
        ///
        /// assert_eq!("🍔∈🌏", s);
        /// ```
        #[stable(feature = "str_mut_extras", since = "1.20.0")]
        #[inline(always)]
        pub unsafe fn as_bytes_mut(&mut self) -> &mut [u8] {
            &mut *(self as *mut str as *mut [u8])
        }

        /// Converts a string slice to a raw pointer.
        ///
        /// As string slices are a slice of bytes, the raw pointer points to a
        /// [`u8`]. This pointer will be pointing to the first byte of the string
        /// slice.
        ///
        /// [`u8`]: primitive.u8.html
        ///
        /// # Examples
        ///
        /// Basic usage:
        ///
        /// ```
        /// let s = "Hello";
        /// let ptr = s.as_ptr();
        /// ```
        #[stable(feature = "rust1", since = "1.0.0")]
        #[inline]
        pub const fn as_ptr(&self) -> *const u8 {
            self as *const str as *const u8
        }

        /// Returns a subslice of `str`.
        ///
        /// This is the non-panicking alternative to indexing the `str`. Returns
        /// [`None`] whenever equivalent indexing operation would panic.
        ///
        /// [`None`]: option/enum.Option.html#variant.None
        ///
        /// # Examples
        ///
        /// ```
        /// let v = String::from("🗻∈🌏");
        ///
        /// assert_eq!(Some("🗻"), v.get(0..4));
        ///
        /// // indices not on UTF-8 sequence boundaries
        /// assert!(v.get(1..).is_none());
        /// assert!(v.get(..8).is_none());
        ///
        /// // out of bounds
        /// assert!(v.get(..42).is_none());
        /// ```
        #[stable(feature = "str_checked_slicing", since = "1.20.0")]
        #[inline]
        pub fn get<I: SliceIndex<str>>(&self, i: I) -> Option<&I::Output> {
            i.get(self)
        }

        /// Returns a mutable subslice of `str`.
        ///
        /// This is the non-panicking alternative to indexing the `str`. Returns
        /// [`None`] whenever equivalent indexing operation would panic.
        ///
        /// [`None`]: option/enum.Option.html#variant.None
        ///
        /// # Examples
        ///
        /// ```
        /// let mut v = String::from("hello");
        /// // correct length
        /// assert!(v.get_mut(0..5).is_some());
        /// // out of bounds
        /// assert!(v.get_mut(..42).is_none());
        /// assert_eq!(Some("he"), v.get_mut(0..2).map(|v| &*v));
        ///
        /// assert_eq!("hello", v);
        /// {
        ///     let s = v.get_mut(0..2);
        ///     let s = s.map(|s| {
        ///         s.make_ascii_uppercase();
        ///         &*s
        ///     });
        ///     assert_eq!(Some("HE"), s);
        /// }
        /// assert_eq!("HEllo", v);
        /// ```
        #[stable(feature = "str_checked_slicing", since = "1.20.0")]
        #[inline]
        pub fn get_mut<I: SliceIndex<str>>(&mut self, i: I) -> Option<&mut I::Output> {
            i.get_mut(self)
        }

        /// Returns a unchecked subslice of `str`.
        ///
        /// This is the unchecked alternative to indexing the `str`.
        ///
        /// # Safety
        ///
        /// Callers of this function are responsible that these preconditions are
        /// satisfied:
        ///
        /// * The starting index must come before the ending index;
        /// * Indexes must be within bounds of the original slice;
        /// * Indexes must lie on UTF-8 sequence boundaries.
        ///
        /// Failing that, the returned string slice may reference invalid memory or
        /// violate the invariants communicated by the `str` type.
        ///
        /// # Examples
        ///
        /// ```
        /// let v = "🗻∈🌏";
        /// unsafe {
        ///     assert_eq!("🗻", v.get_unchecked(0..4));
        ///     assert_eq!("∈", v.get_unchecked(4..7));
        ///     assert_eq!("🌏", v.get_unchecked(7..11));
        /// }
        /// ```
        #[stable(feature = "str_checked_slicing", since = "1.20.0")]
        #[inline]
        pub unsafe fn get_unchecked<I: SliceIndex<str>>(&self, i: I) -> &I::Output {
            i.get_unchecked(self)
        }

        /// Returns a mutable, unchecked subslice of `str`.
        ///
        /// This is the unchecked alternative to indexing the `str`.
        ///
        /// # Safety
        ///
        /// Callers of this function are responsible that these preconditions are
        /// satisfied:
        ///
        /// * The starting index must come before the ending index;
        /// * Indexes must be within bounds of the original slice;
        /// * Indexes must lie on UTF-8 sequence boundaries.
        ///
        /// Failing that, the returned string slice may reference invalid memory or
        /// violate the invariants communicated by the `str` type.
        ///
        /// # Examples
        ///
        /// ```
        /// let mut v = String::from("🗻∈🌏");
        /// unsafe {
        ///     assert_eq!("🗻", v.get_unchecked_mut(0..4));
        ///     assert_eq!("∈", v.get_unchecked_mut(4..7));
        ///     assert_eq!("🌏", v.get_unchecked_mut(7..11));
        /// }
        /// ```
        #[stable(feature = "str_checked_slicing", since = "1.20.0")]
        #[inline]
        pub unsafe fn get_unchecked_mut<I: SliceIndex<str>>(&mut self, i: I) -> &mut I::Output {
            i.get_unchecked_mut(self)
        }

        /// Creates a string slice from another string slice, bypassing safety
        /// checks.
        ///
        /// This is generally not recommended, use with caution! For a safe
        /// alternative see [`str`] and [`Index`].
        ///
        /// [`str`]: primitive.str.html
        /// [`Index`]: ops/trait.Index.html
        ///
        /// This new slice goes from `begin` to `end`, including `begin` but
        /// excluding `end`.
        ///
        /// To get a mutable string slice instead, see the
        /// [`slice_mut_unchecked`] method.
        ///
        /// [`slice_mut_unchecked`]: #method.slice_mut_unchecked
        ///
        /// # Safety
        ///
        /// Callers of this function are responsible that three preconditions are
        /// satisfied:
        ///
        /// * `begin` must come before `end`.
        /// * `begin` and `end` must be byte positions within the string slice.
        /// * `begin` and `end` must lie on UTF-8 sequence boundaries.
        ///
        /// # Examples
        ///
        /// Basic usage:
        ///
        /// ```
        /// let s = "Löwe 老虎 Léopard";
        ///
        /// unsafe {
        ///     assert_eq!("Löwe 老虎 Léopard", s.slice_unchecked(0, 21));
        /// }
        ///
        /// let s = "Hello, world!";
        ///
        /// unsafe {
        ///     assert_eq!("world", s.slice_unchecked(7, 12));
        /// }
        /// ```
        #[stable(feature = "rust1", since = "1.0.0")]
        #[rustc_deprecated(since = "1.29.0", reason = "use `get_unchecked(begin..end)` instead")]
        #[inline]
        pub unsafe fn slice_unchecked(&self, begin: usize, end: usize) -> &str {
            (begin..end).get_unchecked(self)
        }

        /// Creates a string slice from another string slice, bypassing safety
        /// checks.
        /// This is generally not recommended, use with caution! For a safe
        /// alternative see [`str`] and [`IndexMut`].
        ///
        /// [`str`]: primitive.str.html
        /// [`IndexMut`]: ops/trait.IndexMut.html
        ///
        /// This new slice goes from `begin` to `end`, including `begin` but
        /// excluding `end`.
        ///
        /// To get an immutable string slice instead, see the
        /// [`slice_unchecked`] method.
        ///
        /// [`slice_unchecked`]: #method.slice_unchecked
        ///
        /// # Safety
        ///
        /// Callers of this function are responsible that three preconditions are
        /// satisfied:
        ///
        /// * `begin` must come before `end`.
        /// * `begin` and `end` must be byte positions within the string slice.
        /// * `begin` and `end` must lie on UTF-8 sequence boundaries.
        #[stable(feature = "str_slice_mut", since = "1.5.0")]
        #[rustc_deprecated(since = "1.29.0", reason = "use `get_unchecked_mut(begin..end)` instead")]
        #[inline]
        pub unsafe fn slice_mut_unchecked(&mut self, begin: usize, end: usize) -> &mut str {
            (begin..end).get_unchecked_mut(self)
        }

        /// Divide one string slice into two at an index.
        ///
        /// The argument, `mid`, should be a byte offset from the start of the
        /// string. It must also be on the boundary of a UTF-8 code point.
        ///
        /// The two slices returned go from the start of the string slice to `mid`,
        /// and from `mid` to the end of the string slice.
        ///
        /// To get mutable string slices instead, see the [`split_at_mut`]
        /// method.
        ///
        /// [`split_at_mut`]: #method.split_at_mut
        ///
        /// # Panics
        ///
        /// Panics if `mid` is not on a UTF-8 code point boundary, or if it is
        /// beyond the last code point of the string slice.
        ///
        /// # Examples
        ///
        /// Basic usage:
        ///
        /// ```
        /// let s = "Per Martin-Löf";
        ///
        /// let (first, last) = s.split_at(3);
        ///
        /// assert_eq!("Per", first);
        /// assert_eq!(" Martin-Löf", last);
        /// ```
        #[inline]
        #[stable(feature = "str_split_at", since = "1.4.0")]
        pub fn split_at(&self, mid: usize) -> (&str, &str) {
            // is_char_boundary checks that the index is in [0, .len()]
            if self.is_char_boundary(mid) {
                unsafe {
                    (self.get_unchecked(0..mid),
                     self.get_unchecked(mid..self.len()))
                }
            } else {
                slice_error_fail(self, 0, mid)
            }
        }

        /// Divide one mutable string slice into two at an index.
        ///
        /// The argument, `mid`, should be a byte offset from the start of the
        /// string. It must also be on the boundary of a UTF-8 code point.
        ///
        /// The two slices returned go from the start of the string slice to `mid`,
        /// and from `mid` to the end of the string slice.
        ///
        /// To get immutable string slices instead, see the [`split_at`] method.
        ///
        /// [`split_at`]: #method.split_at
        ///
        /// # Panics
        ///
        /// Panics if `mid` is not on a UTF-8 code point boundary, or if it is
        /// beyond the last code point of the string slice.
        ///
        /// # Examples
        ///
        /// Basic usage:
        ///
        /// ```
        /// let mut s = "Per Martin-Löf".to_string();
        /// {
        ///     let (first, last) = s.split_at_mut(3);
        ///     first.make_ascii_uppercase();
        ///     assert_eq!("PER", first);
        ///     assert_eq!(" Martin-Löf", last);
        /// }
        /// assert_eq!("PER Martin-Löf", s);
        /// ```
        #[inline]
        #[stable(feature = "str_split_at", since = "1.4.0")]
        pub fn split_at_mut(&mut self, mid: usize) -> (&mut str, &mut str) {
            // is_char_boundary checks that the index is in [0, .len()]
            if self.is_char_boundary(mid) {
                let len = self.len();
                let ptr = self.as_ptr() as *mut u8;
                unsafe {
                    (from_utf8_unchecked_mut(slice::from_raw_parts_mut(ptr, mid)),
                     from_utf8_unchecked_mut(slice::from_raw_parts_mut(
                        ptr.add(mid),
                        len - mid
                     )))
                }
            } else {
                slice_error_fail(self, 0, mid)
            }
        }

        /// Returns an iterator over the [`char`]s of a string slice.
        ///
        /// As a string slice consists of valid UTF-8, we can iterate through a
        /// string slice by [`char`]. This method returns such an iterator.
        ///
        /// It's important to remember that [`char`] represents a Unicode Scalar
        /// Value, and may not match your idea of what a 'character' is. Iteration
        /// over grapheme clusters may be what you actually want.
        ///
        /// # Examples
        ///
        /// Basic usage:
        ///
        /// ```
        /// let word = "goodbye";
        ///
        /// let count = word.chars().count();
        /// assert_eq!(7, count);
        ///
        /// let mut chars = word.chars();
        ///
        /// assert_eq!(Some('g'), chars.next());
        /// assert_eq!(Some('o'), chars.next());
        /// assert_eq!(Some('o'), chars.next());
        /// assert_eq!(Some('d'), chars.next());
        /// assert_eq!(Some('b'), chars.next());
        /// assert_eq!(Some('y'), chars.next());
        /// assert_eq!(Some('e'), chars.next());
        ///
        /// assert_eq!(None, chars.next());
        /// ```
        ///
        /// Remember, [`char`]s may not match your human intuition about characters:
        ///
        /// ```
        /// let y = "y̆";
        ///
        /// let mut chars = y.chars();
        ///
        /// assert_eq!(Some('y'), chars.next()); // not 'y̆'
        /// assert_eq!(Some('\u{0306}'), chars.next());
        ///
        /// assert_eq!(None, chars.next());
        /// ```
        #[stable(feature = "rust1", since = "1.0.0")]
        #[inline]
        pub fn chars(&self) -> Chars {
            Chars{iter: self.as_bytes().iter()}
        }

        /// Returns an iterator over the [`char`]s of a string slice, and their
        /// positions.
        ///
        /// As a string slice consists of valid UTF-8, we can iterate through a
        /// string slice by [`char`]. This method returns an iterator of both
        /// these [`char`]s, as well as their byte positions.
        ///
        /// The iterator yields tuples. The position is first, the [`char`] is
        /// second.
        ///
        /// # Examples
        ///
        /// Basic usage:
        ///
        /// ```
        /// let word = "goodbye";
        ///
        /// let count = word.char_indices().count();
        /// assert_eq!(7, count);
        ///
        /// let mut char_indices = word.char_indices();
        ///
        /// assert_eq!(Some((0, 'g')), char_indices.next());
        /// assert_eq!(Some((1, 'o')), char_indices.next());
        /// assert_eq!(Some((2, 'o')), char_indices.next());
        /// assert_eq!(Some((3, 'd')), char_indices.next());
        /// assert_eq!(Some((4, 'b')), char_indices.next());
        /// assert_eq!(Some((5, 'y')), char_indices.next());
        /// assert_eq!(Some((6, 'e')), char_indices.next());
        ///
        /// assert_eq!(None, char_indices.next());
        /// ```
        ///
        /// Remember, [`char`]s may not match your human intuition about characters:
        ///
        /// ```
        /// let yes = "y̆es";
        ///
        /// let mut char_indices = yes.char_indices();
        ///
        /// assert_eq!(Some((0, 'y')), char_indices.next()); // not (0, 'y̆')
        /// assert_eq!(Some((1, '\u{0306}')), char_indices.next());
        ///
        /// // note the 3 here - the last character took up two bytes
        /// assert_eq!(Some((3, 'e')), char_indices.next());
        /// assert_eq!(Some((4, 's')), char_indices.next());
        ///
        /// assert_eq!(None, char_indices.next());
        /// ```
        #[stable(feature = "rust1", since = "1.0.0")]
        #[inline]
        pub fn char_indices(&self) -> CharIndices {
            CharIndices { front_offset: 0, iter: self.chars() }
        }

        /// An iterator over the bytes of a string slice.
        ///
        /// As a string slice consists of a sequence of bytes, we can iterate
        /// through a string slice by byte. This method returns such an iterator.
        ///
        /// # Examples
        ///
        /// Basic usage:
        ///
        /// ```
        /// let mut bytes = "bors".bytes();
        ///
        /// assert_eq!(Some(b'b'), bytes.next());
        /// assert_eq!(Some(b'o'), bytes.next());
        /// assert_eq!(Some(b'r'), bytes.next());
        /// assert_eq!(Some(b's'), bytes.next());
        ///
        /// assert_eq!(None, bytes.next());
        /// ```
        #[stable(feature = "rust1", since = "1.0.0")]
        #[inline]
        pub fn bytes(&self) -> Bytes {
            Bytes(self.as_bytes().iter().cloned())
        }

        /// Split a string slice by whitespace.
        ///
        /// The iterator returned will return string slices that are sub-slices of
        /// the original string slice, separated by any amount of whitespace.
        ///
        /// 'Whitespace' is defined according to the terms of the Unicode Derived
        /// Core Property `White_Space`. If you only want to split on ASCII whitespace
        /// instead, use [`split_ascii_whitespace`].
        ///
        /// [`split_ascii_whitespace`]: #method.split_ascii_whitespace
        ///
        /// # Examples
        ///
        /// Basic usage:
        ///
        /// ```
        /// let mut iter = "A few words".split_whitespace();
        ///
        /// assert_eq!(Some("A"), iter.next());
        /// assert_eq!(Some("few"), iter.next());
        /// assert_eq!(Some("words"), iter.next());
        ///
        /// assert_eq!(None, iter.next());
        /// ```
        ///
        /// All kinds of whitespace are considered:
        ///
        /// ```
        /// let mut iter = " Mary   had\ta\u{2009}little  \n\t lamb".split_whitespace();
        /// assert_eq!(Some("Mary"), iter.next());
        /// assert_eq!(Some("had"), iter.next());
        /// assert_eq!(Some("a"), iter.next());
        /// assert_eq!(Some("little"), iter.next());
        /// assert_eq!(Some("lamb"), iter.next());
        ///
        /// assert_eq!(None, iter.next());
        /// ```
        #[stable(feature = "split_whitespace", since = "1.1.0")]
        #[inline]
        pub fn split_whitespace(&self) -> SplitWhitespace {
            SplitWhitespace { inner: self.split(IsWhitespace).filter(IsNotEmpty) }
        }

        /// Split a string slice by ASCII whitespace.
        ///
        /// The iterator returned will return string slices that are sub-slices of
        /// the original string slice, separated by any amount of ASCII whitespace.
        ///
        /// To split by Unicode `Whitespace` instead, use [`split_whitespace`].
        ///
        /// [`split_whitespace`]: #method.split_whitespace
        ///
        /// # Examples
        ///
        /// Basic usage:
        ///
        /// ```
        /// #![feature(split_ascii_whitespace)]
        /// let mut iter = "A few words".split_ascii_whitespace();
        ///
        /// assert_eq!(Some("A"), iter.next());
        /// assert_eq!(Some("few"), iter.next());
        /// assert_eq!(Some("words"), iter.next());
        ///
        /// assert_eq!(None, iter.next());
        /// ```
        ///
        /// All kinds of ASCII whitespace are considered:
        ///
        /// ```
        /// let mut iter = " Mary   had\ta little  \n\t lamb".split_whitespace();
        /// assert_eq!(Some("Mary"), iter.next());
        /// assert_eq!(Some("had"), iter.next());
        /// assert_eq!(Some("a"), iter.next());
        /// assert_eq!(Some("little"), iter.next());
        /// assert_eq!(Some("lamb"), iter.next());
        ///
        /// assert_eq!(None, iter.next());
        /// ```
        #[unstable(feature = "split_ascii_whitespace", issue = "48656")]
        #[inline]
        pub fn split_ascii_whitespace(&self) -> SplitAsciiWhitespace {
            let inner = self
                .as_bytes()
                .split(IsAsciiWhitespace)
                .filter(IsNotEmpty)
                .map(UnsafeBytesToStr);
            SplitAsciiWhitespace { inner }
        }

        /// An iterator over the lines of a string, as string slices.
        ///
        /// Lines are ended with either a newline (`\n`) or a carriage return with
        /// a line feed (`\r\n`).
        ///
        /// The final line ending is optional.
        ///
        /// # Examples
        ///
        /// Basic usage:
        ///
        /// ```
        /// let text = "foo\r\nbar\n\nbaz\n";
        /// let mut lines = text.lines();
        ///
        /// assert_eq!(Some("foo"), lines.next());
        /// assert_eq!(Some("bar"), lines.next());
        /// assert_eq!(Some(""), lines.next());
        /// assert_eq!(Some("baz"), lines.next());
        ///
        /// assert_eq!(None, lines.next());
        /// ```
        ///
        /// The final line ending isn't required:
        ///
        /// ```
        /// let text = "foo\nbar\n\r\nbaz";
        /// let mut lines = text.lines();
        ///
        /// assert_eq!(Some("foo"), lines.next());
        /// assert_eq!(Some("bar"), lines.next());
        /// assert_eq!(Some(""), lines.next());
        /// assert_eq!(Some("baz"), lines.next());
        ///
        /// assert_eq!(None, lines.next());
        /// ```
        #[stable(feature = "rust1", since = "1.0.0")]
        #[inline]
        pub fn lines(&self) -> Lines {
            Lines(self.split_terminator('\n').map(LinesAnyMap))
        }

        /// An iterator over the lines of a string.
        #[stable(feature = "rust1", since = "1.0.0")]
        #[rustc_deprecated(since = "1.4.0", reason = "use lines() instead now")]
        #[inline]
        #[allow(deprecated)]
        pub fn lines_any(&self) -> LinesAny {
            LinesAny(self.lines())
        }

        /// Returns an iterator of `u16` over the string encoded as UTF-16.
        ///
        /// # Examples
        ///
        /// Basic usage:
        ///
        /// ```
        /// let text = "Zażółć gęślą jaźń";
        ///
        /// let utf8_len = text.len();
        /// let utf16_len = text.encode_utf16().count();
        ///
        /// assert!(utf16_len <= utf8_len);
        /// ```
        #[stable(feature = "encode_utf16", since = "1.8.0")]
        pub fn encode_utf16(&self) -> EncodeUtf16 {
            EncodeUtf16 { chars: self.chars(), extra: 0 }
        }

        /// Returns `true` if the given pattern matches a sub-slice of
        /// this string slice.
        ///
        /// Returns `false` if it does not.
        ///
        /// # Examples
        ///
        /// Basic usage:
        ///
        /// ```
        /// let bananas = "bananas";
        ///
        /// assert!(bananas.contains("nana"));
        /// assert!(!bananas.contains("apples"));
        /// ```
        #[stable(feature = "rust1", since = "1.0.0")]
        #[inline]
        pub fn contains<'a, P: Pattern<'a>>(&'a self, pat: P) -> bool {
            pat.is_contained_in(self)
        }

        /// Returns `true` if the given pattern matches a prefix of this
        /// string slice.
        ///
        /// Returns `false` if it does not.
        ///
        /// # Examples
        ///
        /// Basic usage:
        ///
        /// ```
        /// let bananas = "bananas";
        ///
        /// assert!(bananas.starts_with("bana"));
        /// assert!(!bananas.starts_with("nana"));
        /// ```
        #[stable(feature = "rust1", since = "1.0.0")]
        pub fn starts_with<'a, P: Pattern<'a>>(&'a self, pat: P) -> bool {
            pat.is_prefix_of(self)
        }

        /// Returns `true` if the given pattern matches a suffix of this
        /// string slice.
        ///
        /// Returns `false` if it does not.
        ///
        /// # Examples
        ///
        /// Basic usage:
        ///
        /// ```
        /// let bananas = "bananas";
        ///
        /// assert!(bananas.ends_with("anas"));
        /// assert!(!bananas.ends_with("nana"));
        /// ```
        #[stable(feature = "rust1", since = "1.0.0")]
        pub fn ends_with<'a, P: Pattern<'a>>(&'a self, pat: P) -> bool
            where P::Searcher: ReverseSearcher<'a>
        {
            pat.is_suffix_of(self)
        }

        /// Returns the byte index of the first character of this string slice that
        /// matches the pattern.
        ///
        /// Returns [`None`] if the pattern doesn't match.
        ///
        /// The pattern can be a `&str`, [`char`], or a closure that determines if
        /// a character matches.
        ///
        /// [`None`]: option/enum.Option.html#variant.None
        ///
        /// # Examples
        ///
        /// Simple patterns:
        ///
        /// ```
        /// let s = "Löwe 老虎 Léopard";
        ///
        /// assert_eq!(s.find('L'), Some(0));
        /// assert_eq!(s.find('é'), Some(14));
        /// assert_eq!(s.find("Léopard"), Some(13));
        /// ```
        ///
        /// More complex patterns using point-free style and closures:
        ///
        /// ```
        /// let s = "Löwe 老虎 Léopard";
        ///
        /// assert_eq!(s.find(char::is_whitespace), Some(5));
        /// assert_eq!(s.find(char::is_lowercase), Some(1));
        /// assert_eq!(s.find(|c: char| c.is_whitespace() || c.is_lowercase()), Some(1));
        /// assert_eq!(s.find(|c: char| (c < 'o') && (c > 'a')), Some(4));
        /// ```
        ///
        /// Not finding the pattern:
        ///
        /// ```
        /// let s = "Löwe 老虎 Léopard";
        /// let x: &[_] = &['1', '2'];
        ///
        /// assert_eq!(s.find(x), None);
        /// ```
        #[stable(feature = "rust1", since = "1.0.0")]
        #[inline]
        pub fn find<'a, P: Pattern<'a>>(&'a self, pat: P) -> Option<usize> {
            pat.into_searcher(self).next_match().map(|(i, _)| i)
        }

        /// Returns the byte index of the last character of this string slice that
        /// matches the pattern.
        ///
        /// Returns [`None`] if the pattern doesn't match.
        ///
        /// The pattern can be a `&str`, [`char`], or a closure that determines if
        /// a character matches.
        ///
        /// [`None`]: option/enum.Option.html#variant.None
        ///
        /// # Examples
        ///
        /// Simple patterns:
        ///
        /// ```
        /// let s = "Löwe 老虎 Léopard";
        ///
        /// assert_eq!(s.rfind('L'), Some(13));
        /// assert_eq!(s.rfind('é'), Some(14));
        /// ```
        ///
        /// More complex patterns with closures:
        ///
        /// ```
        /// let s = "Löwe 老虎 Léopard";
        ///
        /// assert_eq!(s.rfind(char::is_whitespace), Some(12));
        /// assert_eq!(s.rfind(char::is_lowercase), Some(20));
        /// ```
        ///
        /// Not finding the pattern:
        ///
        /// ```
        /// let s = "Löwe 老虎 Léopard";
        /// let x: &[_] = &['1', '2'];
        ///
        /// assert_eq!(s.rfind(x), None);
        /// ```
        #[stable(feature = "rust1", since = "1.0.0")]
        #[inline]
        pub fn rfind<'a, P: Pattern<'a>>(&'a self, pat: P) -> Option<usize>
            where P::Searcher: ReverseSearcher<'a>
        {
            pat.into_searcher(self).next_match_back().map(|(i, _)| i)
        }

        /// An iterator over substrings of this string slice, separated by
        /// characters matched by a pattern.
        ///
        /// The pattern can be a `&str`, [`char`], or a closure that determines the
        /// split.
        ///
        /// # Iterator behavior
        ///
        /// The returned iterator will be a [`DoubleEndedIterator`] if the pattern
        /// allows a reverse search and forward/reverse search yields the same
        /// elements. This is true for, eg, [`char`] but not for `&str`.
        ///
        /// [`DoubleEndedIterator`]: iter/trait.DoubleEndedIterator.html
        ///
        /// If the pattern allows a reverse search but its results might differ
        /// from a forward search, the [`rsplit`] method can be used.
        ///
        /// [`rsplit`]: #method.rsplit
        ///
        /// # Examples
        ///
        /// Simple patterns:
        ///
        /// ```
        /// let v: Vec<&str> = "Mary had a little lamb".split(' ').collect();
        /// assert_eq!(v, ["Mary", "had", "a", "little", "lamb"]);
        ///
        /// let v: Vec<&str> = "".split('X').collect();
        /// assert_eq!(v, [""]);
        ///
        /// let v: Vec<&str> = "lionXXtigerXleopard".split('X').collect();
        /// assert_eq!(v, ["lion", "", "tiger", "leopard"]);
        ///
        /// let v: Vec<&str> = "lion::tiger::leopard".split("::").collect();
        /// assert_eq!(v, ["lion", "tiger", "leopard"]);
        ///
        /// let v: Vec<&str> = "abc1def2ghi".split(char::is_numeric).collect();
        /// assert_eq!(v, ["abc", "def", "ghi"]);
        ///
        /// let v: Vec<&str> = "lionXtigerXleopard".split(char::is_uppercase).collect();
        /// assert_eq!(v, ["lion", "tiger", "leopard"]);
        /// ```
        ///
        /// A more complex pattern, using a closure:
        ///
        /// ```
        /// let v: Vec<&str> = "abc1defXghi".split(|c| c == '1' || c == 'X').collect();
        /// assert_eq!(v, ["abc", "def", "ghi"]);
        /// ```
        ///
        /// If a string contains multiple contiguous separators, you will end up
        /// with empty strings in the output:
        ///
        /// ```
        /// let x = "||||a||b|c".to_string();
        /// let d: Vec<_> = x.split('|').collect();
        ///
        /// assert_eq!(d, &["", "", "", "", "a", "", "b", "c"]);
        /// ```
        ///
        /// Contiguous separators are separated by the empty string.
        ///
        /// ```
        /// let x = "(///)".to_string();
        /// let d: Vec<_> = x.split('/').collect();
        ///
        /// assert_eq!(d, &["(", "", "", ")"]);
        /// ```
        ///
        /// Separators at the start or end of a string are neighbored
        /// by empty strings.
        ///
        /// ```
        /// let d: Vec<_> = "010".split("0").collect();
        /// assert_eq!(d, &["", "1", ""]);
        /// ```
        ///
        /// When the empty string is used as a separator, it separates
        /// every character in the string, along with the beginning
        /// and end of the string.
        ///
        /// ```
        /// let f: Vec<_> = "rust".split("").collect();
        /// assert_eq!(f, &["", "r", "u", "s", "t", ""]);
        /// ```
        ///
        /// Contiguous separators can lead to possibly surprising behavior
        /// when whitespace is used as the separator. This code is correct:
        ///
        /// ```
        /// let x = "    a  b c".to_string();
        /// let d: Vec<_> = x.split(' ').collect();
        ///
        /// assert_eq!(d, &["", "", "", "", "a", "", "b", "c"]);
        /// ```
        ///
        /// It does _not_ give you:
        ///
        /// ```,ignore
        /// assert_eq!(d, &["a", "b", "c"]);
        /// ```
        ///
        /// Use [`split_whitespace`] for this behavior.
        ///
        /// [`split_whitespace`]: #method.split_whitespace
        #[stable(feature = "rust1", since = "1.0.0")]
        #[inline]
        pub fn split<'a, P: Pattern<'a>>(&'a self, pat: P) -> Split<'a, P> {
            Split(SplitInternal {
                start: 0,
                end: self.len(),
                matcher: pat.into_searcher(self),
                allow_trailing_empty: true,
                finished: false,
            })
        }

        /// An iterator over substrings of the given string slice, separated by
        /// characters matched by a pattern and yielded in reverse order.
        ///
        /// The pattern can be a `&str`, [`char`], or a closure that determines the
        /// split.
        ///
        /// # Iterator behavior
        ///
        /// The returned iterator requires that the pattern supports a reverse
        /// search, and it will be a [`DoubleEndedIterator`] if a forward/reverse
        /// search yields the same elements.
        ///
        /// [`DoubleEndedIterator`]: iter/trait.DoubleEndedIterator.html
        ///
        /// For iterating from the front, the [`split`] method can be used.
        ///
        /// [`split`]: #method.split
        ///
        /// # Examples
        ///
        /// Simple patterns:
        ///
        /// ```
        /// let v: Vec<&str> = "Mary had a little lamb".rsplit(' ').collect();
        /// assert_eq!(v, ["lamb", "little", "a", "had", "Mary"]);
        ///
        /// let v: Vec<&str> = "".rsplit('X').collect();
        /// assert_eq!(v, [""]);
        ///
        /// let v: Vec<&str> = "lionXXtigerXleopard".rsplit('X').collect();
        /// assert_eq!(v, ["leopard", "tiger", "", "lion"]);
        ///
        /// let v: Vec<&str> = "lion::tiger::leopard".rsplit("::").collect();
        /// assert_eq!(v, ["leopard", "tiger", "lion"]);
        /// ```
        ///
        /// A more complex pattern, using a closure:
        ///
        /// ```
        /// let v: Vec<&str> = "abc1defXghi".rsplit(|c| c == '1' || c == 'X').collect();
        /// assert_eq!(v, ["ghi", "def", "abc"]);
        /// ```
        #[stable(feature = "rust1", since = "1.0.0")]
        #[inline]
        pub fn rsplit<'a, P: Pattern<'a>>(&'a self, pat: P) -> RSplit<'a, P>
            where P::Searcher: ReverseSearcher<'a>
        {
            RSplit(self.split(pat).0)
        }

        /// An iterator over substrings of the given string slice, separated by
        /// characters matched by a pattern.
        ///
        /// The pattern can be a `&str`, [`char`], or a closure that determines the
        /// split.
        ///
        /// Equivalent to [`split`], except that the trailing substring
        /// is skipped if empty.
        ///
        /// [`split`]: #method.split
        ///
        /// This method can be used for string data that is _terminated_,
        /// rather than _separated_ by a pattern.
        ///
        /// # Iterator behavior
        ///
        /// The returned iterator will be a [`DoubleEndedIterator`] if the pattern
        /// allows a reverse search and forward/reverse search yields the same
        /// elements. This is true for, eg, [`char`] but not for `&str`.
        ///
        /// [`DoubleEndedIterator`]: iter/trait.DoubleEndedIterator.html
        ///
        /// If the pattern allows a reverse search but its results might differ
        /// from a forward search, the [`rsplit_terminator`] method can be used.
        ///
        /// [`rsplit_terminator`]: #method.rsplit_terminator
        ///
        /// # Examples
        ///
        /// Basic usage:
        ///
        /// ```
        /// let v: Vec<&str> = "A.B.".split_terminator('.').collect();
        /// assert_eq!(v, ["A", "B"]);
        ///
        /// let v: Vec<&str> = "A..B..".split_terminator(".").collect();
        /// assert_eq!(v, ["A", "", "B", ""]);
        /// ```
        #[stable(feature = "rust1", since = "1.0.0")]
        #[inline]
        pub fn split_terminator<'a, P: Pattern<'a>>(&'a self, pat: P) -> SplitTerminator<'a, P> {
            SplitTerminator(SplitInternal {
                allow_trailing_empty: false,
                ..self.split(pat).0
            })
        }

        /// An iterator over substrings of `self`, separated by characters
        /// matched by a pattern and yielded in reverse order.
        ///
        /// The pattern can be a simple `&str`, [`char`], or a closure that
        /// determines the split.
        /// Additional libraries might provide more complex patterns like
        /// regular expressions.
        ///
        /// Equivalent to [`split`], except that the trailing substring is
        /// skipped if empty.
        ///
        /// [`split`]: #method.split
        ///
        /// This method can be used for string data that is _terminated_,
        /// rather than _separated_ by a pattern.
        ///
        /// # Iterator behavior
        ///
        /// The returned iterator requires that the pattern supports a
        /// reverse search, and it will be double ended if a forward/reverse
        /// search yields the same elements.
        ///
        /// For iterating from the front, the [`split_terminator`] method can be
        /// used.
        ///
        /// [`split_terminator`]: #method.split_terminator
        ///
        /// # Examples
        ///
        /// ```
        /// let v: Vec<&str> = "A.B.".rsplit_terminator('.').collect();
        /// assert_eq!(v, ["B", "A"]);
        ///
        /// let v: Vec<&str> = "A..B..".rsplit_terminator(".").collect();
        /// assert_eq!(v, ["", "B", "", "A"]);
        /// ```
        #[stable(feature = "rust1", since = "1.0.0")]
        #[inline]
        pub fn rsplit_terminator<'a, P: Pattern<'a>>(&'a self, pat: P) -> RSplitTerminator<'a, P>
            where P::Searcher: ReverseSearcher<'a>
        {
            RSplitTerminator(self.split_terminator(pat).0)
        }

        /// An iterator over substrings of the given string slice, separated by a
        /// pattern, restricted to returning at most `n` items.
        ///
        /// If `n` substrings are returned, the last substring (the `n`th substring)
        /// will contain the remainder of the string.
        ///
        /// The pattern can be a `&str`, [`char`], or a closure that determines the
        /// split.
        ///
        /// # Iterator behavior
        ///
        /// The returned iterator will not be double ended, because it is
        /// not efficient to support.
        ///
        /// If the pattern allows a reverse search, the [`rsplitn`] method can be
        /// used.
        ///
        /// [`rsplitn`]: #method.rsplitn
        ///
        /// # Examples
        ///
        /// Simple patterns:
        ///
        /// ```
        /// let v: Vec<&str> = "Mary had a little lambda".splitn(3, ' ').collect();
        /// assert_eq!(v, ["Mary", "had", "a little lambda"]);
        ///
        /// let v: Vec<&str> = "lionXXtigerXleopard".splitn(3, "X").collect();
        /// assert_eq!(v, ["lion", "", "tigerXleopard"]);
        ///
        /// let v: Vec<&str> = "abcXdef".splitn(1, 'X').collect();
        /// assert_eq!(v, ["abcXdef"]);
        ///
        /// let v: Vec<&str> = "".splitn(1, 'X').collect();
        /// assert_eq!(v, [""]);
        /// ```
        ///
        /// A more complex pattern, using a closure:
        ///
        /// ```
        /// let v: Vec<&str> = "abc1defXghi".splitn(2, |c| c == '1' || c == 'X').collect();
        /// assert_eq!(v, ["abc", "defXghi"]);
        /// ```
        #[stable(feature = "rust1", since = "1.0.0")]
        #[inline]
        pub fn splitn<'a, P: Pattern<'a>>(&'a self, n: usize, pat: P) -> SplitN<'a, P> {
            SplitN(SplitNInternal {
                iter: self.split(pat).0,
                count: n,
            })
        }

        /// An iterator over substrings of this string slice, separated by a
        /// pattern, starting from the end of the string, restricted to returning
        /// at most `n` items.
        ///
        /// If `n` substrings are returned, the last substring (the `n`th substring)
        /// will contain the remainder of the string.
        ///
        /// The pattern can be a `&str`, [`char`], or a closure that
        /// determines the split.
        ///
        /// # Iterator behavior
        ///
        /// The returned iterator will not be double ended, because it is not
        /// efficient to support.
        ///
        /// For splitting from the front, the [`splitn`] method can be used.
        ///
        /// [`splitn`]: #method.splitn
        ///
        /// # Examples
        ///
        /// Simple patterns:
        ///
        /// ```
        /// let v: Vec<&str> = "Mary had a little lamb".rsplitn(3, ' ').collect();
        /// assert_eq!(v, ["lamb", "little", "Mary had a"]);
        ///
        /// let v: Vec<&str> = "lionXXtigerXleopard".rsplitn(3, 'X').collect();
        /// assert_eq!(v, ["leopard", "tiger", "lionX"]);
        ///
        /// let v: Vec<&str> = "lion::tiger::leopard".rsplitn(2, "::").collect();
        /// assert_eq!(v, ["leopard", "lion::tiger"]);
        /// ```
        ///
        /// A more complex pattern, using a closure:
        ///
        /// ```
        /// let v: Vec<&str> = "abc1defXghi".rsplitn(2, |c| c == '1' || c == 'X').collect();
        /// assert_eq!(v, ["ghi", "abc1def"]);
        /// ```
        #[stable(feature = "rust1", since = "1.0.0")]
        #[inline]
        pub fn rsplitn<'a, P: Pattern<'a>>(&'a self, n: usize, pat: P) -> RSplitN<'a, P>
            where P::Searcher: ReverseSearcher<'a>
        {
            RSplitN(self.splitn(n, pat).0)
        }

        /// An iterator over the disjoint matches of a pattern within the given string
        /// slice.
        ///
        /// The pattern can be a `&str`, [`char`], or a closure that
        /// determines if a character matches.
        ///
        /// # Iterator behavior
        ///
        /// The returned iterator will be a [`DoubleEndedIterator`] if the pattern
        /// allows a reverse search and forward/reverse search yields the same
        /// elements. This is true for, eg, [`char`] but not for `&str`.
        ///
        /// [`DoubleEndedIterator`]: iter/trait.DoubleEndedIterator.html
        ///
        /// If the pattern allows a reverse search but its results might differ
        /// from a forward search, the [`rmatches`] method can be used.
        ///
        /// [`rmatches`]: #method.rmatches
        ///
        /// # Examples
        ///
        /// Basic usage:
        ///
        /// ```
        /// let v: Vec<&str> = "abcXXXabcYYYabc".matches("abc").collect();
        /// assert_eq!(v, ["abc", "abc", "abc"]);
        ///
        /// let v: Vec<&str> = "1abc2abc3".matches(char::is_numeric).collect();
        /// assert_eq!(v, ["1", "2", "3"]);
        /// ```
        #[stable(feature = "str_matches", since = "1.2.0")]
        #[inline]
        pub fn matches<'a, P: Pattern<'a>>(&'a self, pat: P) -> Matches<'a, P> {
            Matches(MatchesInternal(pat.into_searcher(self)))
        }

        /// An iterator over the disjoint matches of a pattern within this string slice,
        /// yielded in reverse order.
        ///
        /// The pattern can be a `&str`, [`char`], or a closure that determines if
        /// a character matches.
        ///
        /// # Iterator behavior
        ///
        /// The returned iterator requires that the pattern supports a reverse
        /// search, and it will be a [`DoubleEndedIterator`] if a forward/reverse
        /// search yields the same elements.
        ///
        /// [`DoubleEndedIterator`]: iter/trait.DoubleEndedIterator.html
        ///
        /// For iterating from the front, the [`matches`] method can be used.
        ///
        /// [`matches`]: #method.matches
        ///
        /// # Examples
        ///
        /// Basic usage:
        ///
        /// ```
        /// let v: Vec<&str> = "abcXXXabcYYYabc".rmatches("abc").collect();
        /// assert_eq!(v, ["abc", "abc", "abc"]);
        ///
        /// let v: Vec<&str> = "1abc2abc3".rmatches(char::is_numeric).collect();
        /// assert_eq!(v, ["3", "2", "1"]);
        /// ```
        #[stable(feature = "str_matches", since = "1.2.0")]
        #[inline]
        pub fn rmatches<'a, P: Pattern<'a>>(&'a self, pat: P) -> RMatches<'a, P>
            where P::Searcher: ReverseSearcher<'a>
        {
            RMatches(self.matches(pat).0)
        }

        /// An iterator over the disjoint matches of a pattern within this string
        /// slice as well as the index that the match starts at.
        ///
        /// For matches of `pat` within `self` that overlap, only the indices
        /// corresponding to the first match are returned.
        ///
        /// The pattern can be a `&str`, [`char`], or a closure that determines
        /// if a character matches.
        ///
        /// # Iterator behavior
        ///
        /// The returned iterator will be a [`DoubleEndedIterator`] if the pattern
        /// allows a reverse search and forward/reverse search yields the same
        /// elements. This is true for, eg, [`char`] but not for `&str`.
        ///
        /// [`DoubleEndedIterator`]: iter/trait.DoubleEndedIterator.html
        ///
        /// If the pattern allows a reverse search but its results might differ
        /// from a forward search, the [`rmatch_indices`] method can be used.
        ///
        /// [`rmatch_indices`]: #method.rmatch_indices
        ///
        /// # Examples
        ///
        /// Basic usage:
        ///
        /// ```
        /// let v: Vec<_> = "abcXXXabcYYYabc".match_indices("abc").collect();
        /// assert_eq!(v, [(0, "abc"), (6, "abc"), (12, "abc")]);
        ///
        /// let v: Vec<_> = "1abcabc2".match_indices("abc").collect();
        /// assert_eq!(v, [(1, "abc"), (4, "abc")]);
        ///
        /// let v: Vec<_> = "ababa".match_indices("aba").collect();
        /// assert_eq!(v, [(0, "aba")]); // only the first `aba`
        /// ```
        #[stable(feature = "str_match_indices", since = "1.5.0")]
        #[inline]
        pub fn match_indices<'a, P: Pattern<'a>>(&'a self, pat: P) -> MatchIndices<'a, P> {
            MatchIndices(MatchIndicesInternal(pat.into_searcher(self)))
        }

        /// An iterator over the disjoint matches of a pattern within `self`,
        /// yielded in reverse order along with the index of the match.
        ///
        /// For matches of `pat` within `self` that overlap, only the indices
        /// corresponding to the last match are returned.
        ///
        /// The pattern can be a `&str`, [`char`], or a closure that determines if a
        /// character matches.
        ///
        /// # Iterator behavior
        ///
        /// The returned iterator requires that the pattern supports a reverse
        /// search, and it will be a [`DoubleEndedIterator`] if a forward/reverse
        /// search yields the same elements.
        ///
        /// [`DoubleEndedIterator`]: iter/trait.DoubleEndedIterator.html
        ///
        /// For iterating from the front, the [`match_indices`] method can be used.
        ///
        /// [`match_indices`]: #method.match_indices
        ///
        /// # Examples
        ///
        /// Basic usage:
        ///
        /// ```
        /// let v: Vec<_> = "abcXXXabcYYYabc".rmatch_indices("abc").collect();
        /// assert_eq!(v, [(12, "abc"), (6, "abc"), (0, "abc")]);
        ///
        /// let v: Vec<_> = "1abcabc2".rmatch_indices("abc").collect();
        /// assert_eq!(v, [(4, "abc"), (1, "abc")]);
        ///
        /// let v: Vec<_> = "ababa".rmatch_indices("aba").collect();
        /// assert_eq!(v, [(2, "aba")]); // only the last `aba`
        /// ```
        #[stable(feature = "str_match_indices", since = "1.5.0")]
        #[inline]
        pub fn rmatch_indices<'a, P: Pattern<'a>>(&'a self, pat: P) -> RMatchIndices<'a, P>
            where P::Searcher: ReverseSearcher<'a>
        {
            RMatchIndices(self.match_indices(pat).0)
        }

        /// Returns a string slice with leading and trailing whitespace removed.
        ///
        /// 'Whitespace' is defined according to the terms of the Unicode Derived
        /// Core Property `White_Space`.
        ///
        /// # Examples
        ///
        /// Basic usage:
        ///
        /// ```
        /// let s = " Hello\tworld\t";
        ///
        /// assert_eq!("Hello\tworld", s.trim());
        /// ```
        #[stable(feature = "rust1", since = "1.0.0")]
        pub fn trim(&self) -> &str {
            self.trim_matches(|c: char| c.is_whitespace())
        }

        /// Returns a string slice with leading whitespace removed.
        ///
        /// 'Whitespace' is defined according to the terms of the Unicode Derived
        /// Core Property `White_Space`.
        ///
        /// # Text directionality
        ///
        /// A string is a sequence of bytes. `start` in this context means the first
        /// position of that byte string; for a left-to-right language like English or
        /// Russian, this will be left side; and for right-to-left languages like
        /// like Arabic or Hebrew, this will be the right side.
        ///
        /// # Examples
        ///
        /// Basic usage:
        ///
        /// ```
        /// let s = " Hello\tworld\t";
        /// assert_eq!("Hello\tworld\t", s.trim_start());
        /// ```
        ///
        /// Directionality:
        ///
        /// ```
        /// let s = "  English  ";
        /// assert!(Some('E') == s.trim_start().chars().next());
        ///
        /// let s = "  עברית  ";
        /// assert!(Some('ע') == s.trim_start().chars().next());
        /// ```
        #[stable(feature = "trim_direction", since = "1.30.0")]
        pub fn trim_start(&self) -> &str {
            self.trim_start_matches(|c: char| c.is_whitespace())
        }

        /// Returns a string slice with trailing whitespace removed.
        ///
        /// 'Whitespace' is defined according to the terms of the Unicode Derived
        /// Core Property `White_Space`.
        ///
        /// # Text directionality
        ///
        /// A string is a sequence of bytes. `end` in this context means the last
        /// position of that byte string; for a left-to-right language like English or
        /// Russian, this will be right side; and for right-to-left languages like
        /// like Arabic or Hebrew, this will be the left side.
        ///
        /// # Examples
        ///
        /// Basic usage:
        ///
        /// ```
        /// let s = " Hello\tworld\t";
        /// assert_eq!(" Hello\tworld", s.trim_end());
        /// ```
        ///
        /// Directionality:
        ///
        /// ```
        /// let s = "  English  ";
        /// assert!(Some('h') == s.trim_end().chars().rev().next());
        ///
        /// let s = "  עברית  ";
        /// assert!(Some('ת') == s.trim_end().chars().rev().next());
        /// ```
        #[stable(feature = "trim_direction", since = "1.30.0")]
        pub fn trim_end(&self) -> &str {
            self.trim_end_matches(|c: char| c.is_whitespace())
        }

        /// Returns a string slice with leading whitespace removed.
        ///
        /// 'Whitespace' is defined according to the terms of the Unicode Derived
        /// Core Property `White_Space`.
        ///
        /// # Text directionality
        ///
        /// A string is a sequence of bytes. 'Left' in this context means the first
        /// position of that byte string; for a language like Arabic or Hebrew
        /// which are 'right to left' rather than 'left to right', this will be
        /// the _right_ side, not the left.
        ///
        /// # Examples
        ///
        /// Basic usage:
        ///
        /// ```
        /// let s = " Hello\tworld\t";
        ///
        /// assert_eq!("Hello\tworld\t", s.trim_left());
        /// ```
        ///
        /// Directionality:
        ///
        /// ```
        /// let s = "  English";
        /// assert!(Some('E') == s.trim_left().chars().next());
        ///
        /// let s = "  עברית";
        /// assert!(Some('ע') == s.trim_left().chars().next());
        /// ```
        #[stable(feature = "rust1", since = "1.0.0")]
        #[rustc_deprecated(reason = "superseded by `trim_start`", since = "1.33.0")]
        pub fn trim_left(&self) -> &str {
            self.trim_start()
        }

        /// Returns a string slice with trailing whitespace removed.
        ///
        /// 'Whitespace' is defined according to the terms of the Unicode Derived
        /// Core Property `White_Space`.
        ///
        /// # Text directionality
        ///
        /// A string is a sequence of bytes. 'Right' in this context means the last
        /// position of that byte string; for a language like Arabic or Hebrew
        /// which are 'right to left' rather than 'left to right', this will be
        /// the _left_ side, not the right.
        ///
        /// # Examples
        ///
        /// Basic usage:
        ///
        /// ```
        /// let s = " Hello\tworld\t";
        ///
        /// assert_eq!(" Hello\tworld", s.trim_right());
        /// ```
        ///
        /// Directionality:
        ///
        /// ```
        /// let s = "English  ";
        /// assert!(Some('h') == s.trim_right().chars().rev().next());
        ///
        /// let s = "עברית  ";
        /// assert!(Some('ת') == s.trim_right().chars().rev().next());
        /// ```
        #[stable(feature = "rust1", since = "1.0.0")]
        #[rustc_deprecated(reason = "superseded by `trim_end`", since = "1.33.0")]
        pub fn trim_right(&self) -> &str {
            self.trim_end()
        }

        /// Returns a string slice with all prefixes and suffixes that match a
        /// pattern repeatedly removed.
        ///
        /// The pattern can be a [`char`] or a closure that determines if a
        /// character matches.
        ///
        /// # Examples
        ///
        /// Simple patterns:
        ///
        /// ```
        /// assert_eq!("11foo1bar11".trim_matches('1'), "foo1bar");
        /// assert_eq!("123foo1bar123".trim_matches(char::is_numeric), "foo1bar");
        ///
        /// let x: &[_] = &['1', '2'];
        /// assert_eq!("12foo1bar12".trim_matches(x), "foo1bar");
        /// ```
        ///
        /// A more complex pattern, using a closure:
        ///
        /// ```
        /// assert_eq!("1foo1barXX".trim_matches(|c| c == '1' || c == 'X'), "foo1bar");
        /// ```
        #[stable(feature = "rust1", since = "1.0.0")]
        pub fn trim_matches<'a, P: Pattern<'a>>(&'a self, pat: P) -> &'a str
            where P::Searcher: DoubleEndedSearcher<'a>
        {
            let mut i = 0;
            let mut j = 0;
            let mut matcher = pat.into_searcher(self);
            if let Some((a, b)) = matcher.next_reject() {
                i = a;
                j = b; // Remember earliest known match, correct it below if
                       // last match is different
            }
            if let Some((_, b)) = matcher.next_reject_back() {
                j = b;
            }
            unsafe {
                // Searcher is known to return valid indices
                self.get_unchecked(i..j)
            }
        }

        /// Returns a string slice with all prefixes that match a pattern
        /// repeatedly removed.
        ///
        /// The pattern can be a `&str`, [`char`], or a closure that determines if
        /// a character matches.
        ///
        /// # Text directionality
        ///
        /// A string is a sequence of bytes. 'Left' in this context means the first
        /// position of that byte string; for a language like Arabic or Hebrew
        /// which are 'right to left' rather than 'left to right', this will be
        /// the _right_ side, not the left.
        ///
        /// # Examples
        ///
        /// Basic usage:
        ///
        /// ```
        /// assert_eq!("11foo1bar11".trim_start_matches('1'), "foo1bar11");
        /// assert_eq!("123foo1bar123".trim_start_matches(char::is_numeric), "foo1bar123");
        ///
        /// let x: &[_] = &['1', '2'];
        /// assert_eq!("12foo1bar12".trim_start_matches(x), "foo1bar12");
        /// ```
        #[stable(feature = "trim_direction", since = "1.30.0")]
        pub fn trim_start_matches<'a, P: Pattern<'a>>(&'a self, pat: P) -> &'a str {
            let mut i = self.len();
            let mut matcher = pat.into_searcher(self);
            if let Some((a, _)) = matcher.next_reject() {
                i = a;
            }
            unsafe {
                // Searcher is known to return valid indices
                self.get_unchecked(i..self.len())
            }
        }

        /// Returns a string slice with all suffixes that match a pattern
        /// repeatedly removed.
        ///
        /// The pattern can be a `&str`, [`char`], or a closure that
        /// determines if a character matches.
        ///
        /// # Text directionality
        ///
        /// A string is a sequence of bytes. 'Right' in this context means the last
        /// position of that byte string; for a language like Arabic or Hebrew
        /// which are 'right to left' rather than 'left to right', this will be
        /// the _left_ side, not the right.
        ///
        /// # Examples
        ///
        /// Simple patterns:
        ///
        /// ```
        /// assert_eq!("11foo1bar11".trim_end_matches('1'), "11foo1bar");
        /// assert_eq!("123foo1bar123".trim_end_matches(char::is_numeric), "123foo1bar");
        ///
        /// let x: &[_] = &['1', '2'];
        /// assert_eq!("12foo1bar12".trim_end_matches(x), "12foo1bar");
        /// ```
        ///
        /// A more complex pattern, using a closure:
        ///
        /// ```
        /// assert_eq!("1fooX".trim_end_matches(|c| c == '1' || c == 'X'), "1foo");
        /// ```
        #[stable(feature = "trim_direction", since = "1.30.0")]
        pub fn trim_end_matches<'a, P: Pattern<'a>>(&'a self, pat: P) -> &'a str
            where P::Searcher: ReverseSearcher<'a>
        {
            let mut j = 0;
            let mut matcher = pat.into_searcher(self);
            if let Some((_, b)) = matcher.next_reject_back() {
                j = b;
            }
            unsafe {
                // Searcher is known to return valid indices
                self.get_unchecked(0..j)
            }
        }

        /// Returns a string slice with all prefixes that match a pattern
        /// repeatedly removed.
        ///
        /// The pattern can be a `&str`, [`char`], or a closure that determines if
        /// a character matches.
        ///
        /// [`char`]: primitive.char.html
        ///
        /// # Text directionality
        ///
        /// A string is a sequence of bytes. 'Left' in this context means the first
        /// position of that byte string; for a language like Arabic or Hebrew
        /// which are 'right to left' rather than 'left to right', this will be
        /// the _right_ side, not the left.
        ///
        /// # Examples
        ///
        /// Basic usage:
        ///
        /// ```
        /// assert_eq!("11foo1bar11".trim_left_matches('1'), "foo1bar11");
        /// assert_eq!("123foo1bar123".trim_left_matches(char::is_numeric), "foo1bar123");
        ///
        /// let x: &[_] = &['1', '2'];
        /// assert_eq!("12foo1bar12".trim_left_matches(x), "foo1bar12");
        /// ```
        #[stable(feature = "rust1", since = "1.0.0")]
        #[rustc_deprecated(reason = "superseded by `trim_start_matches`", since = "1.33.0")]
        pub fn trim_left_matches<'a, P: Pattern<'a>>(&'a self, pat: P) -> &'a str {
            self.trim_start_matches(pat)
        }

        /// Returns a string slice with all suffixes that match a pattern
        /// repeatedly removed.
        ///
        /// The pattern can be a `&str`, [`char`], or a closure that
        /// determines if a character matches.
        ///
        /// [`char`]: primitive.char.html
        ///
        /// # Text directionality
        ///
        /// A string is a sequence of bytes. 'Right' in this context means the last
        /// position of that byte string; for a language like Arabic or Hebrew
        /// which are 'right to left' rather than 'left to right', this will be
        /// the _left_ side, not the right.
        ///
        /// # Examples
        ///
        /// Simple patterns:
        ///
        /// ```
        /// assert_eq!("11foo1bar11".trim_right_matches('1'), "11foo1bar");
        /// assert_eq!("123foo1bar123".trim_right_matches(char::is_numeric), "123foo1bar");
        ///
        /// let x: &[_] = &['1', '2'];
        /// assert_eq!("12foo1bar12".trim_right_matches(x), "12foo1bar");
        /// ```
        ///
        /// A more complex pattern, using a closure:
        ///
        /// ```
        /// assert_eq!("1fooX".trim_right_matches(|c| c == '1' || c == 'X'), "1foo");
        /// ```
        #[stable(feature = "rust1", since = "1.0.0")]
        #[rustc_deprecated(reason = "superseded by `trim_end_matches`", since = "1.33.0")]
        pub fn trim_right_matches<'a, P: Pattern<'a>>(&'a self, pat: P) -> &'a str
            where P::Searcher: ReverseSearcher<'a>
        {
            self.trim_end_matches(pat)
        }

        /// Parses this string slice into another type.
        ///
        /// Because `parse` is so general, it can cause problems with type
        /// inference. As such, `parse` is one of the few times you'll see
        /// the syntax affectionately known as the 'turbofish': `::<>`. This
        /// helps the inference algorithm understand specifically which type
        /// you're trying to parse into.
        ///
        /// `parse` can parse any type that implements the [`FromStr`] trait.
        ///
        /// [`FromStr`]: str/trait.FromStr.html
        ///
        /// # Errors
        ///
        /// Will return [`Err`] if it's not possible to parse this string slice into
        /// the desired type.
        ///
        /// [`Err`]: str/trait.FromStr.html#associatedtype.Err
        ///
        /// # Examples
        ///
        /// Basic usage
        ///
        /// ```
        /// let four: u32 = "4".parse().unwrap();
        ///
        /// assert_eq!(4, four);
        /// ```
        ///
        /// Using the 'turbofish' instead of annotating `four`:
        ///
        /// ```
        /// let four = "4".parse::<u32>();
        ///
        /// assert_eq!(Ok(4), four);
        /// ```
        ///
        /// Failing to parse:
        ///
        /// ```
        /// let nope = "j".parse::<u32>();
        ///
        /// assert!(nope.is_err());
        /// ```
        #[inline]
        #[stable(feature = "rust1", since = "1.0.0")]
        pub fn parse<F: FromStr>(&self) -> Result<F, F::Err> {
            FromStr::from_str(self)
        }

        /// Checks if all characters in this string are within the ASCII range.
        ///
        /// # Examples
        ///
        /// ```
        /// let ascii = "hello!\n";
        /// let non_ascii = "Grüße, Jürgen ❤";
        ///
        /// assert!(ascii.is_ascii());
        /// assert!(!non_ascii.is_ascii());
        /// ```
        #[stable(feature = "ascii_methods_on_intrinsics", since = "1.23.0")]
        #[inline]
        pub fn is_ascii(&self) -> bool {
            // We can treat each byte as character here: all multibyte characters
            // start with a byte that is not in the ascii range, so we will stop
            // there already.
            self.bytes().all(|b| b.is_ascii())
        }

        /// Checks that two strings are an ASCII case-insensitive match.
        ///
        /// Same as `to_ascii_lowercase(a) == to_ascii_lowercase(b)`,
        /// but without allocating and copying temporaries.
        ///
        /// # Examples
        ///
        /// ```
        /// assert!("Ferris".eq_ignore_ascii_case("FERRIS"));
        /// assert!("Ferrös".eq_ignore_ascii_case("FERRöS"));
        /// assert!(!"Ferrös".eq_ignore_ascii_case("FERRÖS"));
        /// ```
        #[stable(feature = "ascii_methods_on_intrinsics", since = "1.23.0")]
        #[inline]
        pub fn eq_ignore_ascii_case(&self, other: &str) -> bool {
            self.as_bytes().eq_ignore_ascii_case(other.as_bytes())
        }

        /// Converts this string to its ASCII upper case equivalent in-place.
        ///
        /// ASCII letters 'a' to 'z' are mapped to 'A' to 'Z',
        /// but non-ASCII letters are unchanged.
        ///
        /// To return a new uppercased value without modifying the existing one, use
        /// [`to_ascii_uppercase`].
        ///
        /// [`to_ascii_uppercase`]: #method.to_ascii_uppercase
        #[stable(feature = "ascii_methods_on_intrinsics", since = "1.23.0")]
        pub fn make_ascii_uppercase(&mut self) {
            let me = unsafe { self.as_bytes_mut() };
            me.make_ascii_uppercase()
        }

        /// Converts this string to its ASCII lower case equivalent in-place.
        ///
        /// ASCII letters 'A' to 'Z' are mapped to 'a' to 'z',
        /// but non-ASCII letters are unchanged.
        ///
        /// To return a new lowercased value without modifying the existing one, use
        /// [`to_ascii_lowercase`].
        ///
        /// [`to_ascii_lowercase`]: #method.to_ascii_lowercase
        #[stable(feature = "ascii_methods_on_intrinsics", since = "1.23.0")]
        pub fn make_ascii_lowercase(&mut self) {
            let me = unsafe { self.as_bytes_mut() };
            me.make_ascii_lowercase()
        }
    }

    #[stable(feature = "rust1", since = "1.0.0")]
    impl AsRef<[u8]> for str {
        #[inline]
        fn as_ref(&self) -> &[u8] {
            self.as_bytes()
        }
    }

    #[stable(feature = "rust1", since = "1.0.0")]
    impl Default for &str {
        /// Creates an empty str
        fn default() -> Self { "" }
    }

    #[stable(feature = "default_mut_str", since = "1.28.0")]
    impl Default for &mut str {
        /// Creates an empty mutable str
        fn default() -> Self { unsafe { from_utf8_unchecked_mut(&mut []) } }
    }

    /// An iterator over the non-whitespace substrings of a string,
    /// separated by any amount of whitespace.
    ///
    /// This struct is created by the [`split_whitespace`] method on [`str`].
    /// See its documentation for more.
    ///
    /// [`split_whitespace`]: ../../std/primitive.str.html#method.split_whitespace
    /// [`str`]: ../../std/primitive.str.html
    #[stable(feature = "split_whitespace", since = "1.1.0")]
    #[derive(Clone, Debug)]
    pub struct SplitWhitespace<'a> {
        inner: Filter<Split<'a, IsWhitespace>, IsNotEmpty>,
    }

    /// An iterator over the non-ASCII-whitespace substrings of a string,
    /// separated by any amount of ASCII whitespace.
    ///
    /// This struct is created by the [`split_ascii_whitespace`] method on [`str`].
    /// See its documentation for more.
    ///
    /// [`split_ascii_whitespace`]: ../../std/primitive.str.html#method.split_ascii_whitespace
    /// [`str`]: ../../std/primitive.str.html
    #[unstable(feature = "split_ascii_whitespace", issue = "48656")]
    #[derive(Clone, Debug)]
    pub struct SplitAsciiWhitespace<'a> {
        inner: Map<Filter<SliceSplit<'a, u8, IsAsciiWhitespace>, IsNotEmpty>, UnsafeBytesToStr>,
    }

    #[derive(Clone)]
    struct IsWhitespace;

    impl FnOnce<(char, )> for IsWhitespace {
        type Output = bool;

        #[inline]
        extern "rust-call" fn call_once(mut self, arg: (char, )) -> bool {
            self.call_mut(arg)
        }
    }

    impl FnMut<(char, )> for IsWhitespace {
        #[inline]
        extern "rust-call" fn call_mut(&mut self, arg: (char, )) -> bool {
            arg.0.is_whitespace()
        }
    }

    #[derive(Clone)]
    struct IsAsciiWhitespace;

    impl<'a> FnOnce<(&'a u8, )> for IsAsciiWhitespace {
        type Output = bool;

        #[inline]
        extern "rust-call" fn call_once(mut self, arg: (&u8, )) -> bool {
            self.call_mut(arg)
        }
    }

    impl<'a> FnMut<(&'a u8, )> for IsAsciiWhitespace {
        #[inline]
        extern "rust-call" fn call_mut(&mut self, arg: (&u8, )) -> bool {
            arg.0.is_ascii_whitespace()
        }
    }

    #[derive(Clone)]
    struct IsNotEmpty;

    impl<'a, 'b> FnOnce<(&'a &'b str, )> for IsNotEmpty {
        type Output = bool;

        #[inline]
        extern "rust-call" fn call_once(mut self, arg: (&'a &'b str, )) -> bool {
            self.call_mut(arg)
        }
    }

    impl<'a, 'b> FnMut<(&'a &'b str, )> for IsNotEmpty {
        #[inline]
        extern "rust-call" fn call_mut(&mut self, arg: (&'a &'b str, )) -> bool {
            !arg.0.is_empty()
        }
    }

    impl<'a, 'b> FnOnce<(&'a &'b [u8], )> for IsNotEmpty {
        type Output = bool;

        #[inline]
        extern "rust-call" fn call_once(mut self, arg: (&'a &'b [u8], )) -> bool {
            self.call_mut(arg)
        }
    }

    impl<'a, 'b> FnMut<(&'a &'b [u8], )> for IsNotEmpty {
        #[inline]
        extern "rust-call" fn call_mut(&mut self, arg: (&'a &'b [u8], )) -> bool {
            !arg.0.is_empty()
        }
    }

    #[derive(Clone)]
    struct UnsafeBytesToStr;

    impl<'a> FnOnce<(&'a [u8], )> for UnsafeBytesToStr {
        type Output = &'a str;

        #[inline]
        extern "rust-call" fn call_once(mut self, arg: (&'a [u8], )) -> &'a str {
            self.call_mut(arg)
        }
    }

    impl<'a> FnMut<(&'a [u8], )> for UnsafeBytesToStr {
        #[inline]
        extern "rust-call" fn call_mut(&mut self, arg: (&'a [u8], )) -> &'a str {
            unsafe { from_utf8_unchecked(arg.0) }
        }
    }

    #[stable(feature = "split_whitespace", since = "1.1.0")]
    impl<'a> Iterator for SplitWhitespace<'a> {
        type Item = &'a str;

        #[inline]
        fn next(&mut self) -> Option<&'a str> {
            self.inner.next()
        }

        #[inline]
        fn size_hint(&self) -> (usize, Option<usize>) {
            self.inner.size_hint()
        }
    }

    #[stable(feature = "split_whitespace", since = "1.1.0")]
    impl<'a> DoubleEndedIterator for SplitWhitespace<'a> {
        #[inline]
        fn next_back(&mut self) -> Option<&'a str> {
            self.inner.next_back()
        }
    }

    #[stable(feature = "fused", since = "1.26.0")]
    impl FusedIterator for SplitWhitespace<'_> {}

    #[unstable(feature = "split_ascii_whitespace", issue = "48656")]
    impl<'a> Iterator for SplitAsciiWhitespace<'a> {
        type Item = &'a str;

        #[inline]
        fn next(&mut self) -> Option<&'a str> {
            self.inner.next()
        }

        #[inline]
        fn size_hint(&self) -> (usize, Option<usize>) {
            self.inner.size_hint()
        }
    }

    #[unstable(feature = "split_ascii_whitespace", issue = "48656")]
    impl<'a> DoubleEndedIterator for SplitAsciiWhitespace<'a> {
        #[inline]
        fn next_back(&mut self) -> Option<&'a str> {
            self.inner.next_back()
        }
    }

    #[unstable(feature = "split_ascii_whitespace", issue = "48656")]
    impl FusedIterator for SplitAsciiWhitespace<'_> {}

    /// An iterator of [`u16`] over the string encoded as UTF-16.
    ///
    /// [`u16`]: ../../std/primitive.u16.html
    ///
    /// This struct is created by the [`encode_utf16`] method on [`str`].
    /// See its documentation for more.
    ///
    /// [`encode_utf16`]: ../../std/primitive.str.html#method.encode_utf16
    /// [`str`]: ../../std/primitive.str.html
    #[derive(Clone)]
    #[stable(feature = "encode_utf16", since = "1.8.0")]
    pub struct EncodeUtf16<'a> {
        chars: Chars<'a>,
        extra: u16,
    }

    #[stable(feature = "collection_debug", since = "1.17.0")]
    impl fmt::Debug for EncodeUtf16<'_> {
        fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
            f.pad("EncodeUtf16 { .. }")
        }
    }

    #[stable(feature = "encode_utf16", since = "1.8.0")]
    impl<'a> Iterator for EncodeUtf16<'a> {
        type Item = u16;

        #[inline]
        fn next(&mut self) -> Option<u16> {
            if self.extra != 0 {
                let tmp = self.extra;
                self.extra = 0;
                return Some(tmp);
            }

            let mut buf = [0; 2];
            self.chars.next().map(|ch| {
                let n = ch.encode_utf16(&mut buf).len();
                if n == 2 {
                    self.extra = buf[1];
                }
                buf[0]
            })
        }

        #[inline]
        fn size_hint(&self) -> (usize, Option<usize>) {
            let (low, high) = self.chars.size_hint();
            // every char gets either one u16 or two u16,
            // so this iterator is between 1 or 2 times as
            // long as the underlying iterator.
            (low, high.and_then(|n| n.checked_mul(2)))
        }
    }

    #[stable(feature = "fused", since = "1.26.0")]
    impl FusedIterator for EncodeUtf16<'_> {}

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