Issue #4085 has been updated by headius (Charles Nutter).


shugo (Shugo Maeda) wrote:
>  I mean that all refinements appear in the method lookup 1.blah, but
>  the only first found one is used, and succeeding super in C outside
>  the scope of using are not affected by other refinements A and B.
>  make sense?

This is exactly right.

>  
>  > |For example,
>  > |
>  > |class X; def blah; puts 'X'; end
>  > |module A; refine(X) { def blah; puts 'A'; super; end }; end

A refines X, and no other refinements are active. super calls X#blah.

>  > |module B; refine(X) { def blah; puts 'B'; super; end }; end

B refines X, and no other refinements are active. super calls X#blah.

>  > |module C; refine(X) { def blah; puts 'C'; super; end }; end

C refines X, and no other refinements are active. super calls X#blah.

>  > |using A; using B; using C
>  > |1.blah
>  >
>  > X.new.blah # <= do you mean X here?
>  
>  Yes.
>  
>  > |Only C and X is called in the above code.
>  > |At first, I thought that stacking refinements and super chain are useful for aspect oriented programming.
>  > |But refinements have no local rebinding, so it might not be a real use case of refinements.
>  >
>  > Fair enough. If we can warn users for conflicted refinements like
>  > above, it's even better.
>  
>  I'd like to hear other opinions, especially Charles' one.

I think you hit the nail on the head. The important concept here is the call site. Each of the super call sites above appears within the context of a *single* refinement, so they should not dispatch to anything but the original method.

This means super chaining should only work in contexts that *nest* refinements, which I think would be exceedingly rare and not really useful (and maybe should simply be an error):

class X; def blah; p 'X'; end; end
module A
  refine X do
    def blah; p 'A'; super; end
    module B
      refine X do
        def blah; p 'B'; super; end
        module C
          refine X do
            def blah; p 'C'; super; end
          end
        end
      end
    end
  end
end

using A::B::C
X.new.blah => C, B, A, X

Or I suppose it could work in the case where A, B, C are included in order into another module, which is then using'ed, since in that case the refinements are supposed to stack?
        
----------------------------------------
Feature #4085: Refinements and nested methods
https://bugs.ruby-lang.org/issues/4085#change-34240

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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