From: "shugo (Shugo Maeda)" <redmine@...>
Date: 2012-11-20T11:45:47+09:00
Subject: [ruby-core:49631] [ruby-trunk - Feature #4085] Refinements and nested methods


Issue #4085 has been updated by shugo (Shugo Maeda).

Assignee changed from shugo (Shugo Maeda) to matz (Yukihiro Matsumoto)

Thanks for your feedback, Charles and others.
I understand your worries.

The feature set of Ruby 2.0 has already been frozen, so it's impossible to introduce a completely different feature in Ruby 2.0.  So we have only the following options:

1. introduce the whole features of Refinements currently implemented
2. introduce some of the features of Refinements (= drop some features)
3. remove all features of Refinements

I think optional features of Refinements are as follows:

A. refinement inheritance in class hierarchies
B. refinement activation for reopened module definitions
C. refinement activation for the string version of module_eval/instance_eval
D. refinement activation for the block version of module_eval/instance_eval

I've asked Matz to decide whether Refinements should be included in Ruby 2.0, and if so, which of these features should be included.

My own take is as follows:

* I'm not sure A is good or not.  It's useful in some cases, but it may be confusing because include doesn't inherit refinements, but class inheritance does.  So it's OK to remove A from Ruby 2.0.
* I want C and D for internal DSLs, but D might be difficult to implement in VMs other than CRuby.  So it's OK to remove D from Ruby 2.0.
  FYI, I'm implementing it without performance overhead when refinements are not used.
    http://shugo.net/tmp/refinement_fix_1119.diff
  In this implementation, refined methods are stored in neither an inline method cache nor the global method cache,
  so there's no need to invalidate cache for module_eval.  I hope D will be introduced in the future.
* From the perspective of consistency, C and D depend on B.  So if C or D is included in Ruby 2.0, B should also be included.

And, I explain some things to clarify my intention.

I have used the word "lexical" to describe Refinements, but by the word I've meant just that Refinements doesn't support local rebinding.  For example, in the following code, FooExt doesn't affect Bar#call_foo even if it's called from Baz, which is a module using FooExt.

  class Foo
  end
  module FooExt
    refine Foo do
      def foo
        puts "foo"
      end
    end
  end
  class Bar
    def call_foo(f)
      f.foo
    end
  end
  module Baz
    using FooExt
    f = Foo.new
    f.foo                # => foo
    Bar.new.call_foo(f)  # => NoMethodError
  end

I think it's the most important feature of Refinements.  Without it, it's hard to avoid conflicts among multiple refinements.

Some people seem to suspect that code using refinements is difficult to debug, but reflection APIs may be useful to debug such code.

  module M
    refine Fixnum do
      def foo; puts "foo" end
    end
  end
  using M
  p 123.method(:foo).owner #=> #<refinement:Fixnum@M>

I admit that Refinements are complex, but it's because issues to address by Refinements are themselves complex.  And, I think Refinements should not be over-used.  Application programmers should not use Refinements.  Refinements are for library/framework programmers.  Besides, even if you're a library or framework programmer, consider other features such as subclassing before Refinements.

----------------------------------------
Feature #4085: Refinements and nested methods
https://bugs.ruby-lang.org/issues/4085#change-33146

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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