cfg_match in core - Rust
Description: A macro for defining `#[cfg]` match-like statements.

# Macro cfg_match

Source

    pub macro cfg_match {
        ({ $($tt:tt)* }) => { ... },
        (_ => { $($output:tt)* }) => { ... },
        (
            $cfg:meta => $output:tt
            $($( $rest:tt )+)?
        ) => { ... },
    }

🔬This is a nightly-only experimental API. (`cfg_match` #115585)
Expand description

A macro for defining `#[cfg]` match-like statements.

It 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.

Trailing `_` wildcard match arms are optional and they indicate a fallback branch when all previous declarations do not evaluate to true.

## §Example

    #![feature(cfg_match)]

    cfg_match! {
        unix => {
            fn foo() { /* unix specific functionality */ }
        }
        target_pointer_width = "32" => {
            fn foo() { /* non-unix, 32-bit functionality */ }
        }
        _ => {
            fn foo() { /* fallback implementation */ }
        }
    }

If desired, it is possible to return expressions through the use of surrounding braces:

    #![feature(cfg_match)]

    let _some_string = cfg_match! {{
        unix => { "With great power comes great electricity bills" }
        _ => { "Behind every successful diet is an unwatched pizza" }
    }};