Tuple Fn

tuplefn.rs

mod private {
    pub trait Sealed<A, R> {}
}

pub trait TupleFn<A, R>: private::Sealed<A, R> {
    fn as_tuple_fn(self) -> impl FnMut(A) -> R;
}

macro_rules! impl_tuple_fns {
    (__emit $($arg:ident),*) => {
        impl<F, R, $($arg,)*> TupleFn<($($arg,)*), R> for F
        where
            F: FnMut($($arg,)*) -> R
        {
            #[inline]
            fn as_tuple_fn(mut self) -> impl FnMut(($($arg,)*)) -> R {
                #[allow(non_snake_case)]
                move |($($arg,)*)| self($($arg,)*) 
            }
        }

        impl<F, R, $($arg,)*> private::Sealed<($($arg,)*), R> for F
        where
            F: FnMut($($arg,)*) -> R
        {}
    };
    ($head:ident, $($tail:ident),+) => {
        impl_tuple_fns!($($tail),+);
        impl_tuple_fns!(__emit $head, $($tail),+);
    };
    ($single:ident) => {
        impl_tuple_fns!(__emit $single);
    };
}

impl_tuple_fns!(M, L, K, J, I, H, G, E, D, C, B, A);