[ruby-core:101132] [Ruby master Feature#17351] Deprecate Random::DEFAULT

Issue #17351 has been updated by Eregon (Benoit Daloze).


It seems pretty rare to need to supply a custom Random instance.
But in such a case, it would be easy to create an explicit one in e.g. the constructor:
```ruby
class Dice
  def initialize(random = Random.new)
    @random = random
  end

  def roll
    @random.rand(6) + 1
  end
end
```

If it needs to scale and run well with parallel threads, the built-in `Kernel#rand` is probably the only good option.

----------------------------------------
Feature #17351: Deprecate Random::DEFAULT
https://bugs.ruby-lang.org/issues/17351#change-88813

* Author: Eregon (Benoit Daloze)
* Status: Open
* Priority: Normal
* Assignee: matz (Yukihiro Matsumoto)
----------------------------------------
From https://bugs.ruby-lang.org/issues/17322#note-11

I think we should deprecate the `Random::DEFAULT` constant, it doesn't make sense anymore and it's longer than using Random class methods (Random.rand) or Kernel instance methods (#rand).
Also, people might expect it to be global.

If users want a Random instance they should just use `Random.new`, not assume there is a global instance in Random::DEFAULT, which is actually rather misleading now (Random::DEFAULT is no longer an instance of Random).

Also note that JRuby & TruffleRuby use a per-thread instance for Kernel#rand, etc, to avoid contention (otherwise it becomes a huge source of contention when threads run in parallel).
Which means on those implementations using Random::DEFAULT was inefficient (extra synchronization).

So for all these reasons I think it's time to deprecate `Random::DEFAULT` and then later remove it (in 3.1?).

I don't think there is any use case for `Random::DEFAULT`, but happy to hear if there is and there is no trivial replacement.



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