How do you pass a Rust function as a parameter?

Question

Can I pass a function as a parameter? If not, what is a good alternative?

I tried some different syntaxes but I have not found the right one. I know I can do this:

Answer 1

Fn, FnMut and FnOnce, outlined in the other answer, are closure types. The types of functions that close over their scope.

Apart from passing closures Rust also supports passing simple (non-closure) functions, like this:

fn times2(value: i32) -> i32 {
    2 * value
}

fn fun_test(value: i32, f: fn(i32) -> i32) -> i32 {
    println!("{}", f (value));
    value
}

fn main() {
    fun_test (2, times2);
}

fn(i32) -> i32 here is a function pointer type.

If you don't need a full-fledged closure than working with function types is often simpler as it doesn't have to deal with those closure lifetime nicities.