Issue #4085 has been updated by dbussink (Dirkjan Bussink).


Here are few points I'd like to make as to why I think the feature should not be part of 2.0. First of all, there is currently not a single idea / design that describes what refinements are. In this issue different approaches and ideas are explored. This is of course a good thing, but it also means that we haven't come to a conclusion.

This means that if refinements were to be part of Ruby 2.0, they would be an implementation that hasn't been fleshed out, is still being debated and can change in the future. I think doing this would be a great disservice to the Ruby community. This is because we would release a feature that people cannot depend on. It may change in the future, break people's code and cause heavy debates on whether we can actually change it in the future.

As a reference, originally in 1.9, Hash being insertion ordered was defined as an implementation detail of CRuby. The position of CRuby in the community however, means that this also turned into spec since people depend on it. This was basically a decision made for us by the community, neither JRuby or Rubinius could say, for us it's not insertion ordered. This means that if some things are released, what is and what is not defined behavior is not always just up to the implementers. The Ruby community will come to expect certain behavior of certain features and depend on it.

If Ruby 2.0 is released without a properly defined way of how refinements work and that they will be supported in that way well into the future, we very well may end up with an implementation that no one really likes but has to be supported indefinitely. 

Ruby is not an experimental language anymore, so asking of the community to accept that this all can change in the future is not the right thing to do. What is part of Ruby the language is something that we should be able to stand behind and say of "we will support this and provide a stable platform for you for the future". If that can't be said of a feature, it should not be added to a released Ruby version.

Even if removing the feature for now is a hard decision, I feel it is the correct. We should not fall into a sunk cost fallacy, where the amount of development on it results in feeling like it could not be removed.

Please realize that nowhere in the argument I've discussed my personal preferences on the feature itself. The thing is that I don't think that should be even necessary at this point, because of all the unclarity about the feature and how it should work.

All in all, I think the Ruby community would be done a great disservice by adding a feature that is still being debated so short before a 2.0 release, does not have clear semantics (looking at the alternatives discussed here) and therefore isn't mature enough to be put out there in the wild. 

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Feature #4085: Refinements and nested methods
https://bugs.ruby-lang.org/issues/4085#change-33803

Author: shugo (Shugo Maeda)
Status: Assigned
Priority: Normal
Assignee: matz (Yukihiro Matsumoto)
Category: core
Target version: 2.0.0


=begin
 As I said at RubyConf 2010, I'd like to propose a new features called
 "Refinements."
 
 Refinements are similar to Classboxes.  However, Refinements doesn't
 support local rebinding as mentioned later.  In this sense,
 Refinements might be more similar to selector namespaces, but I'm not
 sure because I have never seen any implementation of selector
 namespaces.
 
 In Refinements, a Ruby module is used as a namespace (or classbox) for
 class extensions.  Such class extensions are called refinements.  For
 example, the following module refines Fixnum.
 
   module MathN
     refine Fixnum do
       def /(other) quo(other) end
     end
   end
 
 Module#refine(klass) takes one argument, which is a class to be
 extended.  Module#refine also takes a block, where additional or
 overriding methods of klass can be defined.  In this example, MathN
 refines Fixnum so that 1 / 2 returns a rational number (1/2) instead
 of an integer 0.
 
 This refinement can be enabled by the method using.
 
   class Foo
     using MathN
 
     def foo
       p 1 / 2
     end
   end
 
   f = Foo.new
   f.foo #=> (1/2)
   p 1 / 2
 
 In this example, the refinement in MathN is enabled in the definition
 of Foo.  The effective scope of the refinement is the innermost class,
 module, or method where using is called; however the refinement is not
 enabled before the call of using.  If there is no such class, module,
 or method, then the effective scope is the file where using is called.
 Note that refinements are pseudo-lexically scoped.  For example,
 foo.baz prints not "FooExt#bar" but "Foo#bar" in the following code:
 
   class Foo
     def bar
       puts "Foo#bar"
     end
 
     def baz
       bar
     end
   end
 
   module FooExt
     refine Foo do
       def bar
         puts "FooExt#bar"
       end
     end
   end
 
   module Quux
     using FooExt
 
     foo = Foo.new
     foo.bar  # => FooExt#bar
     foo.baz  # => Foo#bar
   end
 
 Refinements are also enabled in reopened definitions of classes using
 refinements and definitions of their subclasses, so they are
 *pseudo*-lexically scoped.
 
   class Foo
     using MathN
   end
 
   class Foo
     # MathN is enabled in a reopened definition.
     p 1 / 2  #=> (1/2)
   end
 
   class Bar < Foo
     # MathN is enabled in a subclass definition.
     p 1 / 2  #=> (1/2)
   end
 
 If a module or class is using refinements, they are enabled in
 module_eval, class_eval, and instance_eval if the receiver is the
 class or module, or an instance of the class.
 
   module A
     using MathN
   end
   class B
     using MathN
   end
   MathN.module_eval do
     p 1 / 2  #=> (1/2)
   end
   A.module_eval do
     p 1 / 2  #=> (1/2)
   end
   B.class_eval do
     p 1 / 2  #=> (1/2)
   end
   B.new.instance_eval do
     p 1 / 2  #=> (1/2)
   end
 
 Besides refinements, I'd like to propose new behavior of nested methods.
 Currently, the scope of a nested method is not closed in the outer method.
 
   def foo
     def bar
       puts "bar"
     end
     bar
   end
   foo  #=> bar
   bar  #=> bar
 
 In Ruby, there are no functions, but only methods.  So there are no
 right places where nested methods are defined.  However, if
 refinements are introduced, a refinement enabled only in the outer
 method would be the right place.  For example, the above code is
 almost equivalent to the following code:
 
   def foo
     klass = self.class
     m = Module.new {
       refine klass do
         def bar
           puts "bar"
         end
       end
     }
     using m
     bar
   end
   foo  #=> bar
   bar  #=> NoMethodError
 
 The attached patch is based on SVN trunk r29837.
=end



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