From: "headius (Charles Nutter)" <headius@...>
Date: 2012-12-01T04:54:20+09:00
Subject: [ruby-core:50412] [ruby-trunk - Feature #4085] Refinements and nested methods


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


Anonymous wrote:
>  |This is incredibly confusing to me. Why are the String refinements active within the refine Array block? That module:
>  |
>  |* Is not within the refine String block
>  |* Is not within a file that uses the String refinement
>  |* Does not refine String
>  |
>  |Why can it see the String refinements even though it's not in a "using" file and not within a refine String block?
>  
>  Because it's within the body of refinement module X. Since both
>  refinements are defined in the same refinement, we consider they are
>  related (you can't see the relation from this silly examples).

I'm still very confused by this. You said this won't work:
module R
  refine String do
    def foo; p :foo; end
  end

  module M
    "".foo
  end
  "".foo
end
"".foo

Shugo posted this example and you replied "Every "".foo in the above example should raise NoMethodError, because they are outside of refine blocks."

However, you go on to say that the example below should work, and I don't understand why:


module R
  refine String do
    def foo; p :foo; end
  end

  module M
    refine(Array) { ... }
    "".foo
  end
  "".foo
end
"".foo

Nothing has changed here; none of the foo calls are within refine blocks, but your example indicates the innermost foo should work. Why?

>  |My idea of *actually* putting refinements into the hierarchy seems like it might fit this best, rather than searching two hierarchies. Will have to think about it more.
>  
>  It makes refinement decoration quite unpredictable.  For example,
>  
>    module M
>      refine Integer do
>        def /(n); self / n.to_f; end
>      end
>    end
>    using M
>    1 / 2 # => you expect 0.5
>  
>  But if refinements are searched through inheritaance hierarchy, it
>  won't work since there's Fixnum#/.

This shouldn't work anyway. Why would we look at refinements for Integer if Fixnum has overridden those methods? This seems completely anti-OO to me. Are you saying refinements can route completely around overridden methods without touching the class that overrides them?

Refinements should apply to a given type, visible to subtypes only if method searching leads it there. We're going to have mass confusion if overridden methods on a subclass can be simply brushed away by refined methods on the superclass. And I'm not even sure how to implement that...we'd have to do a full hierarchy search of all classes looking for refined methods *before* we do a normal search of those same classes. And in your Integer case, what woule super do? Should it call Fixnum#/ or Integer#/? I don't think either is right, and I think being able to route around the overridden methods in a child class is dead wrong.
----------------------------------------
Feature #4085: Refinements and nested methods
https://bugs.ruby-lang.org/issues/4085#change-34237

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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