Assigning nil to fiber storage deletes the association.

[ioquatix]

• Reduce memory allocations when looking up Fiber#storage.

[eregon]

Link: https://bugs.ruby-lang.org/issues/19333

[ioquatix]

I'm happy to not specify this behaviour in Ruby Spec if you think it's an impediment to TruffleRuby using shapes. We can explore the performance trade offs. I'm okay with leaving that behaviour as "under specified" or "implementation defined".

[eregon]

Well, that wouldn't help if user code starts to rely on this.
IMO we shouldn't do this, either have a more explicit method to deal with this, e.g., one taking a block so it's clear it's only set for some duration and cleaned up, or not do it at all since it seems not so much an issue in practice (the same issue exists for Fiber-locals and Thread-locals and is not solved or reported since many years).

The whole design of x-locals with a Symbol key is around having well-named keys and not an automatically-generated part in it.
https://ruby-concurrency.github.io/concurrent-ruby/master/Concurrent/ThreadLocalVar.html is the only real solution for those use-cases of GC-able and anonymous locals.

So my suggestion would be to revert this, because there is no need at this point and it doesn't fully solve the problem either.

[eregon]

I think my comment in https://bugs.ruby-lang.org/issues/19333#note-2 explains clearly that this is not a worthy trade-off.