Macro cfg_match 

cfg_match!() { /* proc-macro */ }

Matches against various cfg settings.

Examples

use osom_lib_cfg_ext::cfg_match;

cfg_match!(
    (target_os = "windows") => {
        fn os_name() -> &'static str {
            "W"
        }
    },
    (target_os = "linux") => {
        fn os_name() -> &'static str {
            "L"
        }
    },
    _ => {
        fn os_name() -> &'static str {
            "U"
        }
    }
);

The call above will generate only one os_name function, depending on the matched condition. The condition is translated to one of #[cfg(...)] attributes.

Conditions are evaluated one after another. In particular the order doesn’t matter if they are independent. However it does matter in general. For example say we have this:

use osom_lib_cfg_ext::cfg_match;

cfg_match!(
    (A) => {
        const A: i32 = 1;
    },
    (B) => {
        const B: i32 = 2;
    }
);

Then if B implies A (as a condition) then B arm will never be matched here. For it to be matched you need to reverse the order:

use osom_lib_cfg_ext::cfg_match;

cfg_match!(
    (B) => {
        const B: i32 = 2;
    },
    (A) => {
        const A: i32 = 1;
    }
);