Cargo

Cargo is a build system (turns Rust code into executable binaries) and a package manager (downloads and compiles project’s dependencies). It’s analogical to node’s npm.

cargo new creates a new project from a standard template. There’s a Cargo.toml file and the src/ directory.

Toml file

The Cargo.toml file contains the project’s metadata (like npm’s project.json). After building the project, Cargo.lock is created as well, which works like project-lock.json of npm. It specifies the exact version numbers of all the dependencies. This way, future builds are reliable. If we want to update some crates, ignoring pinned versions from Cargo.lock, we can run cargo update. It will update the versions (respecting SemVer), and it will also update Cargo.lock with the new versions.

Running

cargo run does the following:

compiles the code in debug mode (for maximal error information) using cargo build
executes the binary

The binaries are produced in /target/debug/ or target/release/.

Release Profiles

Rust apps have two profiles:

dev (used with cargo build) - good defaults for development
release (used with cargo build --release) - good defaults for release builds

These profiles can be customized in the Cargo.toml file. Example:

[profile.dev]
opt-level = 0

[profile.release]
opt-level = 3

The dev profile has 0 optimizations (because we want it to compile fast even though the code runs slower).

Other commands

cargo build - downloads dependencies and compiles the code into an executable binary. It uses the “rustc” compiler behind the scenes.
cargo check - checks if the code compiles, without building the binary. It’s faster than cargo build.
cargo doc - builds HTML documentation for every dependency in the current project.
cargo init - initiates a Rust project with pre-existing files in it. cargo create would create a project from scratch.
cargo add - adds crates. This subcommand needs to be installed first with cargo install cargo-edit.

Crates

Packages are called crates. The open-source ones are shared at https://crates.io.

Binary crates

Binary crates might be installed with cargo install some-crate. They will be installed in the $HOME/.cargo/bin directory.

← Overview

Basics →