rust - How do I clone a closure, so that their types are the same?

Question

I have a struct which looks something like this:

pub struct MyStruct<F>
where
    F: Fn(usize) -> f64,
{
    field: usize,
    mapper: F,
    // fields omitted
}

How do I implement Clone for this struct?

One way I found to copy the function body is:

let mapper = |x| (mystruct.mapper)(x);

But this results in mapper having a different type than that of mystruct.mapper.

playground

Answer 1

As of Rust 1.26.0, closures implement both Copy and Clone if all of the captured variables do:

#[derive(Clone)]
pub struct MyStruct<F>
where
    F: Fn(usize) -> f64,
{
    field: usize,
    mapper: F,
}

fn main() {
    let f = MyStruct {
        field: 34,
        mapper: |x| x as f64,
    };
    let g = f.clone();
    println!("{}", (g.mapper)(3));
}