Conversion from state handlers / reducer dispatchers to callbacks

[its-the-shrimp]

both UseStateHandle and UseReducerDispatcher are currently nothing more than one Rc<dyn Fn>, and I myself recently had a use case for a function that'd extract that function into a callback, what I had to opt for instead was

let setter: UseStateSetter<T>;
let callback = {
  let setter = setter.clone();
  Callback::from(move |x| setter.set(x))
};

Which is way too much code for what's supposed to be a single clone away, so my proposal is adding UseStateSetter::callback(&self) -> Callback<T> & UseReducerDispatcher::callback(&self) -> Callback<T>
What do you think? I'm ready to implement it myself if people agree

[kirillsemyonkin]

The fact they are fns under the hood is an implementation detail that can be used for optimization, your callback (or (in)to_callback) can exist even if that was not the case.

For the time being, you can write an extension trait in your project that does this for you.

In cases you dont want to reuse the setter after, you can avoid a clone, and you dont need Callback::from if it is fed as a prop, since IntoPropValue should convert a lambda to a Callback implicitly.

Also consider #3464.

[futursolo]

Implemented in #3519.