Macro make_extern 

macro_rules! make_extern {
    ( $abi:path, $ty:ty ) => { ... };
}

Convert a function-pointer type to an extern function that uses the specified ABI. Arguments, return type, and safety are preserved.

Example

type F = fn(i32) -> i32;
type C = make_extern!(Abi::C, F);
// `C` is `extern "C" fn(i32) -> i32`

Equivalent to:

with_abi!(Abi::C, F)