Macro std::cfg

macro_rules! cfg {
    ($($cfg : tt) *) => { ... };
}

Evaluates boolean combinations of configuration flags at compile-time.

In addition to the #[cfg] attribute, this macro is provided to allow boolean expression evaluation of configuration flags. This frequently leads to less duplicated code.

The syntax given to this macro is the same syntax as the cfg attribute.

cfg!, unlike #[cfg], does not remove any code and only evaluates to true or false. For example, all blocks in an if/else expression need to be valid when cfg! is used for the condition, regardless of what cfg! is evaluating.

Examples

let my_directory = if cfg!(windows) {
    "windows-specific-directory"
} else {
    "unix-directory"
};