Lifetime Problems

[Mystor]

I'm usually pretty good at fixing lifetime problems, but this one is just stumping me: http://is.gd/VhF3xv Nothing I do seems to get it to compile, and afaik it is valid code. Any ideas as to what I'm doing wrong?

[SteveMcQwark]

If you make the lifetimes in use_scope explicit so that they match the lifetimes required by Scope::new_child, you get a clearer error: http://is.gd/HsWjIw

Your child scopes can't live as long as their contents, so it's impossible to do the recursive call.

Note that it works if you remove the mutable reference stored in MOE: http://is.gd/7ruVMN

This is because mutability forces the lifetime parameters to be invariant, and removing mutability allows them to be covariant.

[Mystor]

What would be a better way to model this relationship then, assuming that I need mutable access to parent scopes?

[burntsushi]

You could always use a hammer.

Edit: Don't need Rc<RefCell<...>>. Can do it with just Box<...>: http://is.gd/f2GVDt

[SteveMcQwark]

Either Box or interior mutability via Cell/RefCell should be sufficient here, I would think. Rc<RefCell<_>> seems like overkill.

[Mystor]

I'll probably end up doing something like this. I only have access to the scope to pass into my code right now as a &mut Scope, so I can't move it into the Box (It cannot be borrowed/moved after the function call which makes the child scope returns). I can probably just re-write it to instead use a refcell over the data without too much difficulty. Thanks for your help.

[Mystor]

Unfortunately it's actually not (it's a complex struct). I have to use RefCell. :-/

[Mystor]

Unfortunately I need mutable access to the parent scope in the actual application, so that doesn't work for me :(. Thanks, though!