Maintaining component state when reparenting

[wokalski]

It is often useful to maintain the state of a component when reparenting or changing the order of elements. Currently you cannot express the former and you express the latter by using keys. The use cases of reparenting are kind of an open question. Replacing key with constant identity stored in state could be an elegant and performant alternative solution for keys. The API would not be cumbersome with Hooks.

In the example below, foo and bar would be passed the same constant identity

let foo = (~contentId as id, children) = component(hooks => {
  <view id />
});

let bar = (~contentId as id, children) = component(hooks => {
  <view id />
});

let baz = () = component(hooks => {
  let (id, hooks) = Hooks.componentId(hooks);
  (hooks, Random.bool() ? <foo contentId=id /> : <bar contentId=id />)
});

An open question is what happens when you render two views with the same component identity at the same time (which is also problematic with keys but you expect keys to break in such cases)