Rust by Example

Configuration conditional checks are possible through two different operators:

• the cfg attribute: #[cfg(...)] in attribute position

• the cfg! macro: cfg!(...) in boolean expressions

While the former enables conditional compilation, the latter conditionally evaluates to true or false literals allowing for checks at run-time. Both utilize identical argument syntax.

// This function only gets compiled if the target OS is linux

#[cfg(target_os = "linux")]

fn are_you_on_linux() {

println!("You are running linux!");

}

// And this function only gets compiled if the target OS is *not* linux

#[cfg(not(target_os = "linux"))]

fn are_you_on_linux() {

println!("You are *not* running linux!");

}

fn main() {

are_you_on_linux();

println!("Are you sure?");

if cfg!(target_os = "linux") {

println!("Yes. It's definitely linux!");

} else {

println!("Yes. It's definitely *not* linux!");

}

}

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