Function aw::functions::function4

pub fn function4<Z, R, A, B, C, D>(f: Z) -> Function<Z, (A, B, C, D), R> where
    Z: FnMut(A, B, C, D) -> R, 

Wraps a type that implements FnMut so that it can be used by hlua.

This is only needed because of a limitation in Rust’s inferrence system.