How to create conditional compilation in Rust

Use the #[cfg(...)] attribute to include or exclude code based on conditions like target OS, debug mode, or custom flags.

#[cfg(target_os = "linux")]
fn run_on_linux() {
    println!("Running on Linux");
}

#[cfg(target_os = "windows")]
fn run_on_windows() {
    println!("Running on Windows");
}

fn main() {
    #[cfg(target_os = "linux")]
    run_on_linux();

    #[cfg(target_os = "windows")]
    run_on_windows();
}

To use custom flags, add them in Cargo.toml under [package.metadata] or pass them via RUSTFLAGS="--cfg my_flag" when compiling.

Conditional compilation lets you include or exclude parts of your code depending on the environment or settings. It is like having different versions of your program that automatically switch based on where or how you run it. This helps you write one codebase that works efficiently on multiple platforms or configurations.