Rust by Example

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: 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);

}

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