[ruby-core:58683] [Backport 200 - Backport #8872] Case statements do not honor a refinement of the '===' method

Issue #8872 has been updated by matz (Yukihiro Matsumoto).


The basic principle of refinements is that refinement do work in local scope.
So methods called from the scope will be refined but method called from methods called will not.

And very importantly, "===" called from case statement is controversial.
It can be viewed as a method called from case statement, or case statement itself is just a syntax sugar wrapping "===" calls.  From the former point of view, refine should not affect "===", but from the latter POV, refinement should change the behavior.

Right now, we took the former POV, and OP expected the latter.
So I would like to hear from others.

Matz.

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Backport #8872: Case statements do not honor a refinement of the '===' method
https://bugs.ruby-lang.org/issues/8872#change-43250

Author: jconley88 (Jon Conley)
Status: Assigned
Priority: Normal
Assignee: matz (Yukihiro Matsumoto)
Category: 
Target version: 


=begin
Below, I've redefined the ((|===|)) method of symbol to always return true.  In ((|RefineTest#uses_refinement|)), I call ((|===|)) directly and the refined method is called.  In ((|RefineTest#does_not_use_refinement|)), the ((|===|)) method is called indirectly through a case statement.  If the refined ((|===|)) method was called, the result should be ((*'The refinement was used'*)), but this code currently returns ((*'The refinement was not used'*)).

 module RefineSymbol
   refine Symbol do
     def ===(other)
       true
     end
   end
 end
 
 using RefineSymbol
 
 class RefineTest
   def uses_refinement
     :a === :b
   end
 
   def does_not_use_refinement
     case :a
     when :b
       'The refinement was used'
     else
       'The refinement was not used'
     end
   end
 end
 
 rt = RefineTest.new
 rt.uses_refinement   # => true
 rt.does_not_use_refinement  # => expected 'The refinement was used' but got 'The refinement was not used'
=end



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