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


Discussed refinements a bit with Matz + ko1 plus a_matsuda and others at lunch...here's summary.

The using method currently touches cref, making it largely scoped like constants. If refinement lookup at a call site proceeds the same way, it would simplify things in my head quite a bit.

Benefits to having refinement lookup follow cref:

* No frame field is necessary
* Easier-to-understand behavior, since the lookup would mimic constant lookup (lexical then hierarchical)

There are down sides:

* module_eval cases would not be possible, since like constant lookup refinements cannot be injected into a scope after the fact
* It is not purely lexical, as I had hoped. However, I recognize that having to "using" in every scope where you want refinements to be active would be painful.
* It may need a global invalidation guard, like constants. It may not, though, since refinements are applied only once, at definition time; so after caching once we may have everything we need for future invalidation.

One concern of mine was avoiding refinement checks at all call sites. With cref-based "using" there's no way to determine at parse time which methods might need refinements. We can determine it at definition time, but the AST is already parsed at that point, so we'd have to rewrite it to have "refined calls" instead of normal calls, or something similar. This also impacts JRuby's ahead-of-time compilation support...we do not have the luxury of running the target code for precompilation, so we can't see if there are refinements active.

For normal runtime jitted code, rewriting the AST or adding a "refined" flag to call nodes may be feasible. Calls can then use a refined call site only in the cases where refinements are active.

For AOT mode, I think the best I can do is to have a flag on the call sites to indicate if refinements are active. If there's no refinements for the first call, there will be no refinements for any future calls, and we can turn that logic off. It would still require that boolean check every time...I don't see a way to eliminate that. (Side note: on invokedynamic, that boolean check would end up free, so it may not be a huge deal long term).

I will attempt to prototype pure cref-based refinement lookup over the next week.
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Feature #4085: Refinements and nested methods
https://bugs.ruby-lang.org/issues/4085#change-32309

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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