From: "headius (Charles Nutter)" <headius@...>
Date: 2012-12-01T05:02:28+09:00
Subject: [ruby-core:50413] [ruby-trunk - Feature #4085] Refinements and nested methods


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


Anonymous wrote:
> Hi,
>  
>  In message "Re: [ruby-core:50355] [ruby-trunk - Feature #4085] Refinements and nested methods"
>      on Fri, 30 Nov 2012 10:43:04 +0900, "trans (Thomas Sawyer)" <transfire@gmail.com> writes:
>  
>  |Then I'd say they refined the wrong class. They should have refined Fixnum. If refining Integer somehow places the refinement in front of Fixnum, then I think all sorts of craziness might ensue.
>  
>  Otherwise the refinement will be more fragile.  Fixnum is
>  implementation detail. For example:
>  
>    class Foo
>    end
>    class FooImpl < Foo
>    end
>    class FooImpl2 < Foo
>    end
>  
>  # FooImpl and FooImpl2 are implementation detail
>  
>    module X
>      refine Foo do
>        def x; ...; end
>      end
>    end
>  
>  # we want to intercept method x of class X (and its subclasses).
>  # we don't want to step in to implementation detail, if possible.

I believe you are incorrect. FooImpl1 and FooImpl2 are not simply implementation details...they're critical parts of the OO hierarchy.

Refinements are supposed to localize monkey-patching, but what you want here is way, way beyond monkey-patching, It's not possible to monkey-patch Foo to have an x method if either FooImpl1 or FooImpl2 define their own. Refinements should not be able to route around overridden methods, or the entire structure of an OO hierarchy becomes meaningless.

>  |  # foo.rb library
>  |  class A
>  |    def x(i); i; end
>  |  end
>  |  class B < A
>  |    def x(i); super ** 2; end
>  |  end
>  |
>  |  A.new.x(3)  #=> 3
>  |  B.new.x(3)  #=> 9
>  |
>  |  # bar.rb
>  |  require 'foo'
>  |  
>  |  module Moo
>  |    refine A do
>  |      def x(i); super + 1; end
>  |    end
>  |  end
>  |
>  |  using Moo
>  |
>  |  A.new.x(3)  #=> 4
>  |  B.new.x(3)  #=> 10  # not 16!?
>  
>  Some may expect 10, and others may expect 16.  We cannot satisfy them
>  all at once.  It's matter of design choice.

Nobody should expect 10...if they do they're simply wrong. B defines its own x method which has been neither monkeypatched nor refined. B's original x should be called.

Refinements should be like extension methods; available for direct calls within some scope (and subscopes), not reflected down the call stack (no method, send, respond_to? tricks), and they should still honor basic OO structure (no routing around overridden methods because a parent is refined).
----------------------------------------
Feature #4085: Refinements and nested methods
https://bugs.ruby-lang.org/issues/4085#change-34238

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



-- 
http://bugs.ruby-lang.org/