Input functions - Rust By Example
Description: Rust by Example (RBE) is a collection of runnable examples that illustrate various Rust concepts and standard libraries.

# Input functions

Since closures may be used as arguments, you might wonder if the same can be said about functions. And indeed they can! If you declare a function that takes a closure as parameter, then any function that satisfies the trait bound of that closure can be passed as a parameter.

    // Define a function which takes a generic `F` argument
    // bounded by `Fn`, and calls it
    fn call_me<F: Fn()>(f: F) {
        f();
    }

    // Define a wrapper function satisfying the `Fn` bound
    fn function() {
        println!("I'm a function!");
    }

    fn main() {
        // Define a closure satisfying the `Fn` bound
        let closure = || println!("I'm a closure!");

        call_me(closure);
        call_me(function);
    }

As an additional note, the `Fn`, `FnMut`, and `FnOnce` `traits` dictate how a closure captures variables from the enclosing scope.

### See also:

`Fn`, `FnMut`, and `FnOnce`