      1
      2
      3
      4
      5
      6
      7
      8
      9
     10
     11
     12
     13
     14
     15
     16
     17
     18
     19
     20
     21
     22
     23
     24
     25
     26
     27
     28
     29
     30
     31
     32
     33
     34
     35
     36
     37
     38
     39
     40
     41
     42
     43
     44
     45
     46
     47
     48
     49
     50
     51
     52
     53
     54
     55
     56
     57
     58
     59
     60
     61
     62
     63
     64
     65
     66
     67
     68
     69
     70
     71
     72
     73
     74
     75
     76
     77
     78
     79
     80
     81
     82
     83
     84
     85
     86
     87
     88
     89
     90
     91
     92
     93
     94
     95
     96
     97
     98
     99
    100
    101
    102
    103
    104
    105
    106
    107
    108
    109
    110
    111
    112
    113
    114
    115
    116
    117
    118
    119
    120
    121
    122
    123
    124
    125
    126
    127
    128
    129
    130
    131
    132
    133
    134
    135
    136
    137
    138
    139
    140
    141
    142
    143
    144
    145
    146
    147
    148
    149
    150
    151
    152
    153
    154
    155
    156
    157
    158
    159
    160
    161
    162
    163
    164
    165
    166
    167
    168
    169
    170
    171
    172
    173
    174
    175
    176
    177
    178
    179
    180
    181
    182
    183
    184
    185
    186
    187
    188
    189
    190
    191
    192
    193
    194
    195
    196
    197
    198
    199
    200
    201
    202
    203
    204
    205
    206
    207
    208
    209
    210
    211
    212
    213
    214
    215
    216
    217
    218
    219
    220
    221
    222
    223
    224
    225
    226
    227
    228
    229
    230
    231
    232
    233
    234
    235
    236
    237
    238
    239
    240
    241
    242
    243
    244
    245
    246
    247
    248
    249
    250
    251
    252
    253
    254
    255
    256
    257
    258
    259
    260
    261
    262
    263
    264
    265
    266
    267
    268
    269
    270
    271
    272
    273
    274
    275
    276
    277
    278
    279
    280
    281
    282
    283
    284
    285
    286
    287
    288
    289
    290
    291
    292
    293
    294
    295
    296
    297
    298
    299
    300
    301
    302
    303
    304
    305
    306
    307
    308
    309
    310
    311
    312
    313
    314
    315
    316
    317
    318
    319
    320
    321
    322
    323
    324
    325
    326
    327
    328
    329
    330
    331
    332
    333
    334
    335
    336
    337
    338
    339
    340
    341
    342
    343
    344
    345
    346
    347
    348
    349
    350
    351
    352
    353
    354
    355
    356
    357
    358
    359
    360
    361
    362
    363
    364
    365
    366
    367
    368
    369
    370
    371
    372
    373
    374
    375
    376
    377
    378
    379
    380
    381
    382
    383
    384
    385
    386
    387
    388
    389
    390
    391
    392
    393
    394
    395
    396
    397
    398
    399
    400
    401
    402
    403
    404
    405
    406
    407
    408
    409
    410
    411
    412
    413
    414
    415
    416
    417
    418
    419
    420
    421

    use convert::TryFrom;
    use mem;
    use ops::{self, Add, Sub};
    use usize;

    use super::{FusedIterator, TrustedLen};

    /// Objects that can be stepped over in both directions.
    ///
    /// The `steps_between` function provides a way to efficiently compare
    /// two `Step` objects.
    #[unstable(feature = "step_trait",
               reason = "likely to be replaced by finer-grained traits",
               issue = "42168")]
    pub trait Step: Clone + PartialOrd + Sized {
        /// Returns the number of steps between two step objects. The count is
        /// inclusive of `start` and exclusive of `end`.
        ///
        /// Returns `None` if it is not possible to calculate `steps_between`
        /// without overflow.
        fn steps_between(start: &Self, end: &Self) -> Option<usize>;

        /// Replaces this step with `1`, returning itself
        fn replace_one(&mut self) -> Self;

        /// Replaces this step with `0`, returning itself
        fn replace_zero(&mut self) -> Self;

        /// Adds one to this step, returning the result
        fn add_one(&self) -> Self;

        /// Subtracts one to this step, returning the result
        fn sub_one(&self) -> Self;

        /// Add an usize, returning None on overflow
        fn add_usize(&self, n: usize) -> Option<Self>;
    }

    // These are still macro-generated because the integer literals resolve to different types.
    macro_rules! step_identical_methods {
        () => {
            #[inline]
            fn replace_one(&mut self) -> Self {
                mem::replace(self, 1)
            }

            #[inline]
            fn replace_zero(&mut self) -> Self {
                mem::replace(self, 0)
            }

            #[inline]
            fn add_one(&self) -> Self {
                Add::add(*self, 1)
            }

            #[inline]
            fn sub_one(&self) -> Self {
                Sub::sub(*self, 1)
            }
        }
    }

    macro_rules! step_impl_unsigned {
        ($($t:ty)*) => ($(
            #[unstable(feature = "step_trait",
                       reason = "likely to be replaced by finer-grained traits",
                       issue = "42168")]
            impl Step for $t {
                #[inline]
                #[allow(trivial_numeric_casts)]
                fn steps_between(start: &$t, end: &$t) -> Option<usize> {
                    if *start < *end {
                        // Note: We assume $t <= usize here
                        Some((*end - *start) as usize)
                    } else {
                        Some(0)
                    }
                }

                #[inline]
                #[allow(unreachable_patterns)]
                fn add_usize(&self, n: usize) -> Option<Self> {
                    match <$t>::try_from(n) {
                        Ok(n_as_t) => self.checked_add(n_as_t),
                        Err(_) => None,
                    }
                }

                step_identical_methods!();
            }
        )*)
    }
    macro_rules! step_impl_signed {
        ($( [$t:ty : $unsigned:ty] )*) => ($(
            #[unstable(feature = "step_trait",
                       reason = "likely to be replaced by finer-grained traits",
                       issue = "42168")]
            impl Step for $t {
                #[inline]
                #[allow(trivial_numeric_casts)]
                fn steps_between(start: &$t, end: &$t) -> Option<usize> {
                    if *start < *end {
                        // Note: We assume $t <= isize here
                        // Use .wrapping_sub and cast to usize to compute the
                        // difference that may not fit inside the range of isize.
                        Some((*end as isize).wrapping_sub(*start as isize) as usize)
                    } else {
                        Some(0)
                    }
                }

                #[inline]
                #[allow(unreachable_patterns)]
                fn add_usize(&self, n: usize) -> Option<Self> {
                    match <$unsigned>::try_from(n) {
                        Ok(n_as_unsigned) => {
                            // Wrapping in unsigned space handles cases like
                            // `-120_i8.add_usize(200) == Some(80_i8)`,
                            // even though 200_usize is out of range for i8.
                            let wrapped = (*self as $unsigned).wrapping_add(n_as_unsigned) as $t;
                            if wrapped >= *self {
                                Some(wrapped)
                            } else {
                                None  // Addition overflowed
                            }
                        }
                        Err(_) => None,
                    }
                }

                step_identical_methods!();
            }
        )*)
    }

    macro_rules! step_impl_no_between {
        ($($t:ty)*) => ($(
            #[unstable(feature = "step_trait",
                       reason = "likely to be replaced by finer-grained traits",
                       issue = "42168")]
            impl Step for $t {
                #[inline]
                fn steps_between(_start: &Self, _end: &Self) -> Option<usize> {
                    None
                }

                #[inline]
                fn add_usize(&self, n: usize) -> Option<Self> {
                    self.checked_add(n as $t)
                }

                step_identical_methods!();
            }
        )*)
    }

    step_impl_unsigned!(usize u8 u16);
    #[cfg(not(target_pointer_width = "16"))]
    step_impl_unsigned!(u32);
    #[cfg(target_pointer_width = "16")]
    step_impl_no_between!(u32);
    step_impl_signed!([isize: usize] [i8: u8] [i16: u16]);
    #[cfg(not(target_pointer_width = "16"))]
    step_impl_signed!([i32: u32]);
    #[cfg(target_pointer_width = "16")]
    step_impl_no_between!(i32);
    #[cfg(target_pointer_width = "64")]
    step_impl_unsigned!(u64);
    #[cfg(target_pointer_width = "64")]
    step_impl_signed!([i64: u64]);
    // If the target pointer width is not 64-bits, we
    // assume here that it is less than 64-bits.
    #[cfg(not(target_pointer_width = "64"))]
    step_impl_no_between!(u64 i64);
    step_impl_no_between!(u128 i128);

    macro_rules! range_exact_iter_impl {
        ($($t:ty)*) => ($(
            #[stable(feature = "rust1", since = "1.0.0")]
            impl ExactSizeIterator for ops::Range<$t> { }
        )*)
    }

    macro_rules! range_incl_exact_iter_impl {
        ($($t:ty)*) => ($(
            #[stable(feature = "inclusive_range", since = "1.26.0")]
            impl ExactSizeIterator for ops::RangeInclusive<$t> { }
        )*)
    }

    macro_rules! range_trusted_len_impl {
        ($($t:ty)*) => ($(
            #[unstable(feature = "trusted_len", issue = "37572")]
            unsafe impl TrustedLen for ops::Range<$t> { }
        )*)
    }

    macro_rules! range_incl_trusted_len_impl {
        ($($t:ty)*) => ($(
            #[unstable(feature = "trusted_len", issue = "37572")]
            unsafe impl TrustedLen for ops::RangeInclusive<$t> { }
        )*)
    }

    #[stable(feature = "rust1", since = "1.0.0")]
    impl<A: Step> Iterator for ops::Range<A> {
        type Item = A;

        #[inline]
        fn next(&mut self) -> Option<A> {
            if self.start < self.end {
                // We check for overflow here, even though it can't actually
                // happen. Adding this check does however help llvm vectorize loops
                // for some ranges that don't get vectorized otherwise,
                // and this won't actually result in an extra check in an optimized build.
                if let Some(mut n) = self.start.add_usize(1) {
                    mem::swap(&mut n, &mut self.start);
                    Some(n)
                } else {
                    None
                }
            } else {
                None
            }
        }

        #[inline]
        fn size_hint(&self) -> (usize, Option<usize>) {
            match Step::steps_between(&self.start, &self.end) {
                Some(hint) => (hint, Some(hint)),
                None => (0, None)
            }
        }

        #[inline]
        fn nth(&mut self, n: usize) -> Option<A> {
            if let Some(plus_n) = self.start.add_usize(n) {
                if plus_n < self.end {
                    self.start = plus_n.add_one();
                    return Some(plus_n)
                }
            }

            self.start = self.end.clone();
            None
        }

        #[inline]
        fn last(mut self) -> Option<A> {
            self.next_back()
        }

        #[inline]
        fn min(mut self) -> Option<A> {
            self.next()
        }

        #[inline]
        fn max(mut self) -> Option<A> {
            self.next_back()
        }
    }

    // These macros generate `ExactSizeIterator` impls for various range types.
    // Range<{u,i}64> and RangeInclusive<{u,i}{32,64,size}> are excluded
    // because they cannot guarantee having a length <= usize::MAX, which is
    // required by ExactSizeIterator.
    range_exact_iter_impl!(usize u8 u16 u32 isize i8 i16 i32);
    range_incl_exact_iter_impl!(u8 u16 i8 i16);

    // These macros generate `TrustedLen` impls.
    //
    // They need to guarantee that .size_hint() is either exact, or that
    // the upper bound is None when it does not fit the type limits.
    range_trusted_len_impl!(usize isize u8 i8 u16 i16 u32 i32 i64 u64);
    range_incl_trusted_len_impl!(usize isize u8 i8 u16 i16 u32 i32 i64 u64);

    #[stable(feature = "rust1", since = "1.0.0")]
    impl<A: Step> DoubleEndedIterator for ops::Range<A> {
        #[inline]
        fn next_back(&mut self) -> Option<A> {
            if self.start < self.end {
                self.end = self.end.sub_one();
                Some(self.end.clone())
            } else {
                None
            }
        }
    }

    #[stable(feature = "fused", since = "1.26.0")]
    impl<A: Step> FusedIterator for ops::Range<A> {}

    #[stable(feature = "rust1", since = "1.0.0")]
    impl<A: Step> Iterator for ops::RangeFrom<A> {
        type Item = A;

        #[inline]
        fn next(&mut self) -> Option<A> {
            let mut n = self.start.add_one();
            mem::swap(&mut n, &mut self.start);
            Some(n)
        }

        #[inline]
        fn size_hint(&self) -> (usize, Option<usize>) {
            (usize::MAX, None)
        }

        #[inline]
        fn nth(&mut self, n: usize) -> Option<A> {
            let plus_n = self.start.add_usize(n).expect("overflow in RangeFrom::nth");
            self.start = plus_n.add_one();
            Some(plus_n)
        }
    }

    #[stable(feature = "fused", since = "1.26.0")]
    impl<A: Step> FusedIterator for ops::RangeFrom<A> {}

    #[unstable(feature = "trusted_len", issue = "37572")]
    unsafe impl<A: Step> TrustedLen for ops::RangeFrom<A> {}

    #[stable(feature = "inclusive_range", since = "1.26.0")]
    impl<A: Step> Iterator for ops::RangeInclusive<A> {
        type Item = A;

        #[inline]
        fn next(&mut self) -> Option<A> {
            self.compute_is_empty();
            if self.is_empty.unwrap_or_default() {
                return None;
            }
            let is_iterating = self.start < self.end;
            self.is_empty = Some(!is_iterating);
            Some(if is_iterating {
                let n = self.start.add_one();
                mem::replace(&mut self.start, n)
            } else {
                self.start.clone()
            })
        }

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

            match Step::steps_between(&self.start, &self.end) {
                Some(hint) => (hint.saturating_add(1), hint.checked_add(1)),
                None => (0, None),
            }
        }

        #[inline]
        fn nth(&mut self, n: usize) -> Option<A> {
            self.compute_is_empty();
            if self.is_empty.unwrap_or_default() {
                return None;
            }

            if let Some(plus_n) = self.start.add_usize(n) {
                use cmp::Ordering::*;

                match plus_n.partial_cmp(&self.end) {
                    Some(Less) => {
                        self.is_empty = Some(false);
                        self.start = plus_n.add_one();
                        return Some(plus_n)
                    }
                    Some(Equal) => {
                        self.is_empty = Some(true);
                        return Some(plus_n)
                    }
                    _ => {}
                }
            }

            self.is_empty = Some(true);
            None
        }

        #[inline]
        fn last(mut self) -> Option<A> {
            self.next_back()
        }

        #[inline]
        fn min(mut self) -> Option<A> {
            self.next()
        }

        #[inline]
        fn max(mut self) -> Option<A> {
            self.next_back()
        }
    }

    #[stable(feature = "inclusive_range", since = "1.26.0")]
    impl<A: Step> DoubleEndedIterator for ops::RangeInclusive<A> {
        #[inline]
        fn next_back(&mut self) -> Option<A> {
            self.compute_is_empty();
            if self.is_empty.unwrap_or_default() {
                return None;
            }
            let is_iterating = self.start < self.end;
            self.is_empty = Some(!is_iterating);
            Some(if is_iterating {
                let n = self.end.sub_one();
                mem::replace(&mut self.end, n)
            } else {
                self.end.clone()
            })
        }
    }

    #[stable(feature = "fused", since = "1.26.0")]
    impl<A: Step> FusedIterator for ops::RangeInclusive<A> {}

# Help

## Keyboard Shortcuts

`?`
  Show this help dialog
`S`
  Focus the search field
`↑`
  Move up in search results
`↓`
  Move down in search results
`↹`
  Switch tab
`⏎`
  Go to active search result
`+`
  Expand all sections
`-`
  Collapse all sections

## Search Tricks

Prefix searches with a type followed by a colon (e.g., `fn:`) to restrict the search to a given type.

Accepted types are: `fn`, `mod`, `struct`, `enum`, `trait`, `type`, `macro`, and `const`.

Search functions by type signature (e.g., `vec -> usize` or `* -> vec`)

Search multiple things at once by splitting your query with comma (e.g., `str,u8` or `String,struct:Vec,test`)