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|
//! Macros for conditional compilation.
/// Compile-time matching on config variables.
///
/// Only the branch relevant on your machine will be type-checked!
///
/// # Example
///
/// ```
/// # #[macro_use] extern crate mac;
/// # fn main() {
/// let mascot = match_cfg! {
/// (target_os = "linux") => "penguin",
/// (target_os = "openbsd") => "blowfish",
/// _ => "unknown",
/// };
/// println!("{}", mascot);
/// # }
/// ```
///
#[macro_export]
macro_rules! match_cfg {
( $( ($cfg:meta) => $e:expr, )* _ => $last:expr, ) => {
match () {
$(
#[cfg($cfg)]
() => $e,
)*
#[cfg(all( $( not($cfg) ),* ))]
() => $last,
}
};
( $( ($cfg:meta) => $e:expr, )* ) => {
match_cfg! {
$(
($cfg) => $e,
)*
_ => {
#[allow(dead_code)]
#[static_assert]
static MATCH_CFG_FALLBACK_UNREACHABLE: bool = false;
}
}
};
}
/// Compile-time conditional expression.
///
/// # Example
///
/// ```
/// # #[macro_use] extern crate mac;
/// # fn main() {
/// if_cfg!(test {
/// println!("Crate built as a test suite");
/// })
/// # }
/// ```
///
/// Unlike `if cfg!(...)`, this will not even compile the unused branch.
///
/// ```
/// # #[macro_use] extern crate mac;
/// # fn main() {
/// let x = if_cfg!(any(bleh, blah="bluh") {
/// some_undefined_function_name();
/// 2 + "doesn't even typecheck"
/// } else {
/// 3
/// });
///
/// assert_eq!(x, 3);
/// # }
/// ```
#[macro_export]
macro_rules! if_cfg {
($cfg:meta $t:block else $f:block) => {
match_cfg! {
($cfg) => $t,
_ => $f,
}
};
($cfg:meta $t:block) => {
if_cfg!($cfg $t else { })
};
}
|
