How to use features in Cargo

Use features in Cargo by defining them in the [features] section of your Cargo.toml and enabling them via the --features flag or conditional compilation. Define feature groups and dependencies, then activate them during build or test commands.

[features]
default = ["std"]
std = []
advanced = ["std", "dep:regex"]

[dependencies]
regex = { version = "1.10", optional = true }

Enable features when building or testing:

cargo build --features advanced
cargo test --features std

Use conditional compilation in your code:

#[cfg(feature = "advanced")]
use regex;

Features let you turn parts of your Rust project on or off, like optional modules in an app. You define what each feature includes in your config file and switch them on when building or testing. It’s like having different versions of your software ready to go without changing the code.