## Creating a New Package

To start a new package with Cargo, use `cargo new`:

    $ cargo new hello_world --bin

We’re passing `--bin` because we’re making a binary program: if we were making a library, we’d pass `--lib`. This also initializes a new `git` repository by default. If you don't want it to do that, pass `--vcs none`.

Let’s check out what Cargo has generated for us:

    $ cd hello_world
    $ tree .
    .
    ├── Cargo.toml
    └── src
        └── main.rs

    1 directory, 2 files

Let’s take a closer look at `Cargo.toml`:

    [package]
    name = "hello_world"
    version = "0.1.0"
    authors = ["Your Name <you@example.com>"]
    edition = "2018"

    [dependencies]

This is called a manifest, and it contains all of the metadata that Cargo needs to compile your package.

Here’s what’s in `src/main.rs`:

    fn main() {
        println!("Hello, world!");
    }

Cargo generated a “hello world” for us. Let’s compile it:

    $ cargo build
       Compiling hello_world v0.1.0 (file:///path/to/package/hello_world)

And then run it:

    $ ./target/debug/hello_world
    Hello, world!

We can also use `cargo run` to compile and then run it, all in one step (You won't see the `Compiling` line if you have not made any changes since you last compiled):

    $ cargo run
       Compiling hello_world v0.1.0 (file:///path/to/package/hello_world)
         Running `target/debug/hello_world`
    Hello, world!

You’ll now notice a new file, `Cargo.lock`. It contains information about our dependencies. Since we don’t have any yet, it’s not very interesting.

Once you’re ready for release, you can use `cargo build --release` to compile your files with optimizations turned on:

    $ cargo build --release
       Compiling hello_world v0.1.0 (file:///path/to/package/hello_world)

`cargo build --release` puts the resulting binary in `target/release` instead of `target/debug`.

Compiling in debug mode is the default for development-- compilation time is shorter since the compiler doesn't do optimizations, but the code will run slower. Release mode takes longer to compile, but the code will run faster.