How to fix the warning about unused Boxed trait object

[jgilray]

I've created some callback code based on the stackoverflow example. The code works, but I don't understand how to fix a warning I'm getting. I thought I might need to call drop() explicitly, but I can't make that work.

Here is the code:

Rust Playground

Thanks,
-jgilray

[daboross]

Since the warning isn't valid - you don't actually want to call this function - you really just need to silence the warning. Both let _ = ... and an explicit drop will do this:

let _ = self.callbacks.remove(id);
// or (less commonly used):
drop(self.callbacks.remove(id));

let _ = ... is fairly common, and should be read as "I don't care about the result, and I explicitly telling the compiler that". I mostly see it when ignoring Results, but it should work for other #[must_use] types as well.

[jgilray]

Thanks @daboross!