Shared via Rust Playground

playground.rs

trait Star<Ret> {
    type F: ?Sized;

    fn star(self, f: &Self::F) -> Ret;
}

macro_rules! star_impl {
    ($($n:ident),*) => {
        impl<Ret,$($n),*> Star<Ret> for ($($n,)*) {
            type F = Fn($($n),*) -> Ret;
        
            #[allow(non_snake_case)]
            fn star(self, f: &Self::F) -> Ret {
                let ($($n,)*) = self;
                f($($n),*)
            }
        }
    }
}

star_impl!();
star_impl!(A);
star_impl!(A, B);
star_impl!(A, B, C);
star_impl!(A, B, C, D);
star_impl!(A, B, C, D, E);

fn foo(i: isize, s: &str, b: bool) -> String {
    format!("{} {} {}", i, s, b)
}

fn main() {
    println!("{}", ().star(&|| "hi"));
    println!("{}", (1,).star(&|x| x+5));
    println!("{}", (1, "2").star(&|x, y| x+y.parse::<isize>().unwrap()));
    println!("{}", (1, "2", true).star(&foo));
}