Macro feature 

macro_rules! feature {
    (if ($name:literal) { $then1:expr } else $(if $condition:tt { $then2:expr } else)* { $else:expr }) => { ... };
    (if (!$name:literal) { $then1:expr } else $(if $condition:tt { $then2:expr } else)* { $else:expr }) => { ... };
    ({ $else:expr }) => { ... };
}

Compiles expressions conditionally on features.

Examples

use cfg_exif::expr::feature;

assert_eq!(
    feature!(if ("foo") {
        0
    } else if (!"bar") {
        42
    } else {
        1
    }),
    42
);