Crates

Table of Contents

Rust calls libraries crates. Management of crates is generally done through cargo, but this is not strictly necessary.

Usage of libraries

In Rust 2015 you need to declare crates via the extern crate-statement.

extern crate serde_json;

use serde_json::Value;

fn main() {
    let data = r#" { "name": "John Doe", "age": 43, ... } "#;
    let v: Value = serde_json::from_str(data)?;
    println!(
        "Please call {} at the number {}", 
        v["name"], 
        v["phones"][0]
    );
}

This imports the "SERialisation/DEserialisation"-Framework.

Rust 2018 onwards this is no longer required. Libraries that were declared via cargo can simply be used with use-statements.

use serde_json::{self, Value};

fn main() {
    let data = r#" { "name": "John Doe", "age": 43, ... } "#;
    let v: Value = serde_json::from_str(data)?;
    println!(
        "Please call {} at the number {}", 
        v["name"], 
        v["phones"][0]
    );
}

Macro usage

Since Rust 2018 you no longer have to explicitly import macros, they work just like functions.

Simply call a macro as follows

use bar::baz;

fn main() {
	baz!(); // I am a macro!
}

You might still encounter older Rust code which relies on #[macro_use]

Crates can be renamed, just like normal use statements:

use serde_json as json;

fn main() {
	crate::json::some_function();
}

Note the crate keyword before its usage. You’re using a local alias. The original still exists.

Alternative: rename dependencies via cargo:

[dependencies]
foo = { git = "svnexpress.com/user/mylib", package = "foo" }
bar = { version = "0.1", package = "actually_its_bar_these_days" }

crates.io

Published crates can be found on crates.io, their documentation is automatically published to docs.rs.

Crates and Applications

cargo install my_crate installs the applications shipped with a crate.