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.