Feature #19377
Updated by zverok (Victor Shepelev) almost 2 years ago
Justification:
* `#storage`, which pretends to be an instance method, is always available only on `Fiber.current`, which is [problematic to document](https://github.com/ruby/ruby/pull/6985#discussion_r1055796069), and needs special handling when `storage` is called for non-current Fiber;
* with class method + docs "storage of the current fiber" it all will be self-evident;
* Most of the time, when we declare methods that are available only in the current {something}, they are class methods. (like storage's itself interface of `Fiber::[]` and `Fiber::[]=`, or `Module.used_modules`, which is modules and refinements of the _current context_, but it is not `self.used_modules`, for example)
* Code like
```ruby
Fiber.current.storage = {foo: 'bar'}
Fiber[:foo]
```
...looks like it is two unrelated things (storage of the _current_ fiber vs some "global" key getter/setter?)
I don't see much discussion of this in #19078. Matz in #19078#note-22, 19078#note-22, while accepting the interface, describes it as homogenous:
> (1) fiber[key]/fiber[key]=val - accepted.
> (2) fiber.storage => hash - accepted
> (3) fiber.storage=hash - should be experimental
> ...
So I believe it should be either `Fiber.current[]` and `Fiber.current.storage`, or `Fiber[]`, and `Fiber.storage`. The latter is preferable to underline it is only one, related to the current fiber, interface, not "every fiber instance has one (but actually you can use only `current`'s)