RefCell-less use_mut_ref

[ColonelThirtyTwo]

use_mut_ref forcibly wraps the value in a RefCell, which is sometimes not ideal and isn't an obligation (next_state returns an Rc<T>). In particular, if the inner structure needs to split up access into multiple RefCells to partition access, or uses other methods of interior mutability, the top-level RefCell is just extra overhead.

[hamza1311]

How do you this should be be implemented? I can't think of a way to handle mutability without RefCell here

[ColonelThirtyTwo]

@hamza1311 Cell, Atomic*, channels, or anything else that has interior mutability nested inside of it. Or cases where mutable access needs to be split:

struct Watcher(Rc<MyState>);

struct MyState {
    value: RefCell<i32>
    watcher: RefCell<Watcher>,
}
impl MyState {
    fn notify_watcher(&self) {
        let watcher = self.watcher.borrow_mut();
        watcher.notify();
    }
}
impl Watcher {
    fn notify(&mut self) {
        println!("{}", *self.0.value.borrow())
    }
}

An oversimplification, but it demonstrates the issue: this can't work with a single top-level RefCell because MyState::notify_watcher needs mutable access to run Watcher::notify, but Watcher::notify needs access to the value.

tldr move the interior mutability to the user, who has a better idea of what they need.

[hamza1311]

Would you like to create a PR this change? I would be happy to take a look at one.

You can find the relevant source code in packages/yew/functional/use_ref.rs

[ColonelThirtyTwo]

#3548