Macro with_output 

macro_rules! with_output {
    ( $out:ty, $ty:ty ) => { ... };
}

Construct a function-pointer type identical to the given one but using the specified return type.

Examples

type F = extern "C" fn(i32) -> i32;
type G = with_output!(u64, F);
// `G` is `extern "C" fn(i32) -> u64`