Add third-party crates to your project

3 minutes

In this module, we'll learn how to add third-party crates to your project. Rust standard library doesn't have a module for regular expressions, so let's add the regex crate that's available at Crates.io. This website is the Rust community's central package registry that serves as a location to discover and download packages.

Whenever we want to add dependent crates to our project, we can rely on Cargo to do all the heavy lifting for us. To depend on a library hosted on crates.io, add it to your Cargo.toml file:

[dependencies]
regex = "1.4.2"

If your Cargo.toml doesn't already have a [dependencies] section, add that section. Then list the crate name and version that you want to use.

The next step is to run the command cargo build. Cargo will fetch the new dependency and all of its dependencies, and compile them all:

    $ cargo build
        Updating crates.io index
      Downloaded regex v1.4.2
      Downloaded thread_local v1.0.1
      Downloaded regex-syntax v0.6.21
      Downloaded lazy_static v1.4.0
      Downloaded aho-corasick v0.7.15
      Downloaded memchr v2.3.4
      Downloaded 6 crates (689.7 KB) in 4.58s
       Compiling memchr v2.3.4
       Compiling lazy_static v1.4.0
       Compiling regex-syntax v0.6.21
       Compiling thread_local v1.0.1
       Compiling aho-corasick v0.7.15
       Compiling regex v1.4.2
       Compiling my-project v0.1.0 (/home/user/code/my-project)
        Finished dev [unoptimized + debuginfo] target(s) in 35.13s

We can now use the regex library in our main.rs:

use regex::Regex;

fn main() {
    let re = Regex::new(r"^\d{4}-\d{2}-\d{2}$").unwrap();
    println!("Did our date match? {}", re.is_match("2014-01-01"));
}

Running it will show:

    $ cargo run
       Running `target/hello_world`
    Did our date match? true

You can also use third-party crates in the Rust Playground.

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