[ruby-core:53450] [ruby-trunk - Feature #6308] Eliminate delegation from WeakRef

Issue #6308 has been updated by headius (Charles Nutter).


I request a ruling by matz for making the backward-incompatible change of having Weakref no longer be a Delegate. Alternatively, make it a Delegate where all delegated methods warn that you shouldn't use it as a Delegate.

If necessary I will move this feature request to CommonRuby.
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Feature #6308: Eliminate delegation from WeakRef
https://bugs.ruby-lang.org/issues/6308#change-37634

Author: headius (Charles Nutter)
Status: Assigned
Priority: Normal
Assignee: matz (Yukihiro Matsumoto)
Category: lib
Target version: next minor


WeakRef's delegation features are a really awful pattern that should not be allowed in future versions of Ruby.

WeakRef makes no guarantees as to the liveness of its contained object. It can be collected at any time if there are no strong references to it.

WeakRef currently uses delegation to pass method calls through to the contained object. This encourages a pattern where a WeakRef is passed to methods that expect to have a reference to the underlying object, making it appear to be that object.

Unfortunately, this is *never* a good idea. Because the object can be collected at any time, you may get a nil reference from __getobj__ *arbitrarily* in code that tries to call methods against the given WeakRef. That means using WeakRef as a delegate will always result in unreliable code, and errors may happen for inexplicable reasons.

I believe Ruby 2.0 should eliminate WeakRef's delegation features and make it a simple reference holder. There's no safe way to use a weak reference except to grab a reference to the object, check that it is alive (non-nil) and then proceed with the use of the object, as follows:

obj = weakref.__getobj__
raise AppropriateError unless obj
obj.do_something
obj.do_something_else

Along with eliminating delegation, I would recommend simply making the get method #get, since the uglier #__getobj__ is only named that way because it is not delegated.


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