Thesis:

>The application event loop coalesces these damage rectangles and initiates an optimized operation: it only redraws views whose bounds intersect the damaged region, and also passes the rectangle(s) to the drawRect:: method. (That's why it's called drawRect::).

So, according to this, you need an explicit run-time mechanism to optimize the interaction of parents with children, with some form of coalescing.

Antithesis:

>This is another reason why it's advantageous to have a stable hierarchy of stateful objects representing your UI. If you need more context, you just ask around. Ask your parent, ask your siblings, ask your children, they are all present. Again, no special magic needed.

...except here, where OP says you don't need any special magic to deal with parent/child relationships: just reach up/down/left/right and do your thing!

Synthesis:

The reason one-way data flow became so popular is exactly because the second view is a trap, or at least, a local maximum. If you are really doing complicated orchestration in your hierarchy, then you will end up reinventing the first wheel, to avoid expensive/inefficient parent/child/parent thrashing cascades.

React does in fact have a good solution for this, in the form of contexts. These also allow you to reach up and go talk to parents, in a controlled yet composable way. The way I describe them is "singletons but with scope". An underappreciated benefit is that you can extend a parent context and pass it down, replicating some of the benefits of inheritance, without the messyness of subclasses.

Where React falls short is that parents can't respond to children without re-rendering themselves, which ironically makes implementing e.g. nested tree widgets hard, even though the result is all tree-shaped.

Functional effect systems which can re-join after forking, and gather yielded values, do not have this issue, and I wish React would explore this avenue instead of the all the React 18 stuff they've been doing lately... it feels too much like they are leaning into the same Facebook "dumb read-only UI" style that the article correctly laments. They are straying away from React's original appeal, which was that it was "just the V in MVC", and instead becoming very opinionated on how server side and client side should be combined. Meanwhile the challenges of how to replicate complex legacy desktop UIs remain mostly unaddressed, with the official advice about event handlers, state and effects falling short by a mile.