Crate cfg_if

source ·
Expand description

A macro for defining #[cfg] if-else statements.

The macro provided by this crate, cfg_if, is similar to the if/elif C preprocessor macro by allowing definition of a cascade of #[cfg] cases, emitting the implementation which matches first.

This allows you to conveniently provide a long list #[cfg]’d blocks of code without having to rewrite each clause multiple times.


cfg_if::cfg_if! {
    if #[cfg(unix)] {
        fn foo() { /* unix specific functionality */ }
    } else if #[cfg(target_pointer_width = "32")] {
        fn foo() { /* non-unix, 32-bit functionality */ }
    } else {
        fn foo() { /* fallback implementation */ }


  • The main macro provided by this crate. See crate documentation for more information.