Macro cfg_table 

macro_rules! cfg_table {
    () => { ... };
    (_ => $expr:expr,) => { ... };
    ([$cfg:meta] => $expr:expr, $($tail:tt)*) => { ... };
    (32 => $expr:expr, $($tail:tt)*) => { ... };
    (64 => $expr:expr, $($tail:tt)*) => { ... };
    ("32" => $expr:expr, $($tail:tt)*) => { ... };
    ("64" => $expr:expr, $($tail:tt)*) => { ... };
    (macos => $expr:expr, $($tail:tt)*) => { ... };
    (linux => $expr:expr, $($tail:tt)*) => { ... };
    (windows => $expr:expr, $($tail:tt)*) => { ... };
    (macos32 => $expr:expr, $($tail:tt)*) => { ... };
    (macos64 => $expr:expr, $($tail:tt)*) => { ... };
    (linux32 => $expr:expr, $($tail:tt)*) => { ... };
    (linux64 => $expr:expr, $($tail:tt)*) => { ... };
    (win32 => $expr:expr, $($tail:tt)*) => { ... };
    (win64 => $expr:expr, $($tail:tt)*) => { ... };
}

A simple macro that expands to different values across compilation targets.

Note, that you must have a leading , in the macro invocation.

Panics

This macro will panic at runtime if no matching value is found.

Example

let var = cfg_table! {
    [all(target_os = "freebsd", target_pointer_width = "64", feature = "my-feature")] => 1337, // custom

    // common platforms
    win32 => 32,
    win64 => 64,
    linux32 => 32,
    linux64 => 64,
    macos32 => 32,
    macos64 => 64,

    // pointer widths
    32 => 1985,
    "32" => 1985,
    64 => 2003,
    "64" => 2003,

    _ => 123, // default value if nothing matches, this must be at the bottom
};

cfg_table! {
    win32 => {
        println!("You're on Windows 32-bit!");
    },

    win64 => {
        println!("You're on Windows 64-bit!");
    },

    _ => {
        panic!("What the heck is a \"Linux\"?");
    },
};