Forum: Ruby-core Refinements and nested methods

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


The8472 (Aaron G) wrote:
>     module RefinementInheritor
>       def extended(base)
>         base.send(:using, FooExt)
>         # or
>         base.module_eval "using FooExt"
>       end
>     end

The above code cannot activate refinements in the caller context.
That is, a NoMethodError is raised in the following example:

module FooExt
  refine String do
    def foo
      puts "foo"
    end
  end
end

module RefinementInheritor
  def self.included(mod)
    mod.send(:using, FooExt)
    # or
    mod.module_eval "using FooExt"
  end
end

module Foo
  include RefinementInheritor

  p "abc".foo #=> NoMethodError
end

>  I was thinking about
>
>     Proc.new.rebind_refinements(TargetClass)
>
>  since this would only allow a single scope per proc at any given time
>  which might make optimizations easier. But maybe your way would work too.

What happens if the receiver of rebind_refinements has already been 
called before rebind_refinements?

  p = Proc.new { ... }
  p.call
  p.rebind_refinements(TargetClass)
  p.call

>  alias-method-chain to_proc? Would it use the wrong scope? Would things
>  break?

Do you mean to redefine Symbol#to_proc yourself?  If so, it's impossible 
to close refinements in the caller context of Symbol#to_proc into the 
created Proc.

>  .__send__ and .method obviously suffer from the same issues of shifting
>  stack frames and aliasing. Other metaprogramming things might be
>  expected to do the "right thing(tm)" too and thus would have to rely on
>  stack inspection which is an absolute minefield in Ruby.

__send__ and .method work the same as Symbol#to_proc in the current 
implementation.

>  Should the anonymous refinement module be mutable? E.g. by adding some
>  respond_to_missing to it?

Currently respond_to_missing doesn't work in a refinement module.

module FooExt
  refine String do
    def respond_to_missing?(mid, include_all)
      mid == :foo
    end

    def method_missing(mid, *args)
      if mid == :foo
        puts "foo!"
      else
        super
      end
    end
  end
end

using FooExt

if "abc".respond_to?(:foo) #=> false
  "abc".foo
end

I guess respond_to? need to be fixed to make the above code work.

>  Has anyone even defined how metaprogramming should work with refinements?

I think, in principle, metaprogramming APIs related to method 
dispatching should use refinements in the caller context.

----------------------------------------
Feature #4085: Refinements and nested methods
https://bugs.ruby-lang.org/issues/4085#change-33464

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