Forum: Ruby-core Refinements and nested methods

45196398e9685000d195ec626d477f0e?d=identicon&s=25 Thomas Sawyer (7rans)
on 2012-11-30 02:45
(Received via mailing list)
Issue #4085 has been updated by trans (Thomas Sawyer).


=begin
> But if refinements are searched through inheritaance hierarchy, it
> won't work since there's Fixnum#/.

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. Consider:

  # 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!?

=end

----------------------------------------
Feature #4085: Refinements and nested methods
https://bugs.ruby-lang.org/issues/4085#change-34173

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
6738588a11b852833edf6aec90ef6fa3?d=identicon&s=25 Yukihiro Matsumoto (Guest)
on 2012-11-30 03:14
(Received via mailing list)
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.

|  # 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.

              matz.
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