Code shared from the Rust Playground

playground.rs

fn hoge(x: i32) -> i32 {
    x + 1
}
fn fuga(y: i32) -> i32 {
    y * 2
}

fn main() {
    let mut f: Box<dyn Fn(i32) -> i32> = Box::new(hoge);

    println!("{}", f(15));

    f = Box::new(fuga);

    println!("{}", f(20));
}