One of the core points about metaobject protocols is that while it's important to language design, a good language to me also exposes & makes flexible the object system to users of the language too.

From a review (https://www.adamtornhill.com/reviews/amop.htm),

> The metaobject protocol behaves like an interface towards the language itself, available for the programmer to incrementally customize. Just as we can specialize and extend the behavior of the classes we define in our own applications, we can now extend the language itself using the very same mechanisms.

One of the points that has rather surprised me is that we devs have not more broadly explored what we could do with our metaobject protocols. We havent had a boom in metaprogramming, we haven't seen a largescale return of AOP; we've been letting objects stay dumb unextended objects for a long time now.

The one sizable exception I have on my radar is React's Higher Order Components, where components/classes were wrapped/composed in other classes. Slices of object behavior were spliced into place.

Now that's replaced with hooks, which invert the relationship, making the function up front composed all behavior it might want as hooks that it calls.

I don't know enough about how Rust macros are made & used. My vague impression is they are very scarcely considered. Maybe I just missed the discussions but I'd expect there to be lots of blogging about this topic if metaprogramming here was really as fertile a field here as to be expected.