Forum: Ruby-core Refinements and nested methods

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


shugo (Shugo Maeda) wrote:
> headius (Charles Nutter) wrote:
> > Well, I'm still questioning how super should work in general. Refinements are 
not actually modifying class hierarchy, so the current behavior of super calling 
the old method seems like magic to me.
>
> It may seem magical, but is intended for use like aspect oriented programming.

The interaction between super chains and refinements bothers me.

A new idea...

Because we'd like refinements to act like they live in the class 
hierarchy...let's just make them live in the class hierarchy.

So...we start out with String < Object. Do a refinement:

module X
  refine String do
    def blah; end
  end
end

Now the String hierarchy looks like this: RefinedByX < String < Object

It's rather prepend-like. Lookup proceeds as normal for a given string 
by getting the metaclass (now RefinedByX). However when refined 
intermediate classes are encountered, the calling scope is queried to 
see if it has activated that refinement.

CallSite pseudo-code:

metaclass = obj.metaclass
while metaclass != null
  if metaclass.refinement?
    unless caller_scope.include_refinement? metaclass
      # skip refinement
      metaclass = metaclass.superclass
      next
    end
  end

  method = metaclass.search_method method_name
  return method if method
  metaclass = metaclass.superclass
end

Super logic than can operate as it should, using the refined scope to do 
the subsequent super lookup, which it finds in the hierarchy in the 
normal way. Caching also proceeds largely the same, based on the target 
object's hierarchy only; the only difference is whether refined elements 
in the hierarchy are included in the search.

Not sure about other edge cases for this, but it's another way to look 
at it, and I think this starts to move refinements more directly toward 
being structured in the same way as module inclusion rather than based 
on the more magical concept of "current frame overlay modules".
----------------------------------------
Feature #4085: Refinements and nested methods
https://bugs.ruby-lang.org/issues/4085#change-34056

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