Callback in struct

callback.rs

struct Foo {
  callback: Option<Box<dyn Fn()>>,
}

impl Foo {
  fn new() -> Self {
    Self {
      callback: None,
    }
  }
  
  fn set_callback<C>(&mut self, cb: C)
    where
        C: Fn() + 'static,
  {
    self.callback = Some(Box::new(cb));
  }
  
  fn call_callback(&self) {
    self.callback.as_ref().map(|cb|cb());
  }
}