pub macro cfg_match { ( $(cfg($initial_meta:meta) => { $($initial_tokens:item)* })+ _ => { $($extra_tokens:item)* } ) => { ... }, ($(cfg($extra_meta:meta) => { $($extra_tokens:item)* })*) => { ... }, (@ __items($($_:meta,)*);) => { ... }, ( @ __items($($no:meta,)*); (($($yes:meta)?) ($($tokens:item)*)), $($rest:tt,)* ) => { ... }, (@ __identity $($tokens:item)*) => { ... }, }
🔬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! {
cfg(unix) => {
fn foo() { /* unix specific functionality */ }
}
cfg(target_pointer_width = "32") => {
fn foo() { /* non-unix, 32-bit functionality */ }
}
_ => {
fn foo() { /* fallback implementation */ }
}
}
Run