Passing a closure to a generic function

I have a function that takes a const generic value and a closure.

pub fn parse<const N: usize, F>(consumer: F) 
    where F: Fn(usize)
{
    consumer(N * 2);
}

The function compiles fine. But I get a compile error when I try to call it.

parse::<10>(|n| {
    println!("Closure called with: {}", n);
});

The error is:

this function takes 2 generic arguments but 1 generic argument was supplied

I used a type placeholder and it actually worked.

parse::<10, _>(|n| {
    println!("Closure called with: {}", n);
});

Is there no other elegant way of doing this? If the const generics wasn’t there then Rust will have no problem inferring the closure type.

>Solution :

You can use a so-called "impl trait in argument positon" instead of a generic type parameter:

pub fn parse<const N: usize>(consumer: impl Fn(usize))
{
    consumer(N * 2);
}

This is very similar to your original code, except that the type of consumer must always be implicit and cannot be explicitly specified with type parameters.