“error: closure may outlive the current function” but it will not outlive it

Question

When I try to compile the following code:

fn main() {

    (...)

    let mut should_end = false;

    let mut input = Input::new(ctx);

    input.add_handle         


        

Answer 1

The problem is not your closure, but the add_handler method. Fully expanded it would look like this:

fn add_handler<'a>(&'a mut self, handler: Box)

As you can see, there's an implicit 'static bound on the trait object. Obviously we don't want that, so we introduce a second lifetime 'b:

fn add_handler<'a, 'b: 'a>(&'a mut self, handler: Box)

Since you are adding the handler object to the Input::handlers field, that field cannot outlive the scope of the handler object. Thus we also need to limit its lifetime:

pub struct Input<'a> {
    handlers: Vec>,
}

This again requires the impl to have a lifetime, which we can use in the add_handler method.

impl<'a> Input<'a> {
    ...
    pub fn add_handler(&mut self, handler: Box) {
        self.handlers.push(handler);
    }
}

Now all that's left is using a Cell to control access to your should_end flag.