From: "headius (Charles Nutter)" <headius@...>
Date: 2012-11-30T04:05:15+09:00
Subject: [ruby-core:50338] [ruby-trunk - Feature #4085] Refinements and nested methods


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


Anonymous wrote:
> In message "Re: [ruby-core:50299] [ruby-trunk - Feature #4085] Refinements and nested methods"
>  |How should the following code behave?
>  |
>  |module R
>  |  refine String do
>  |    def foo; p :foo; end
>  |  end
>  |  "".foo # (a)
>  |end
>  |"".foo   # (b)
>  |
>  |Currently, (a) prints :foo, and (b) raises a NoMethodError.
>  
>  Refinements will be available only from:
>  
>  * the scope where refinements are added by calling "using"
>  * or inside of refine blocks
>  
>  Inside of refine blocks (not whole module scope) might be
>  controversial, but I think it's OK to restrict refinements there.  As
>  a result, both (a) and (b) raise NoMethodError.  But "".foo can be called
>  from within the refine block.

I assume this is so that refinement methods will see each other, yes?

module X
  refine String do
    def foo; :foo; end
    def bar; foo; end # should be able to call foo
  end
end

So all call sites within a refine block must look for refinements. Now...I would assume they can only see refinements in the same block, but...

>  Every "".foo in the above example should raise NoMethodError, because
>  they are outside of refine blocks.  I admit I've been less careful
>  about nested refinement modules.  For nested refinement modules, it
>  should behave as following:
>  
>  >module R
>  >  refine String do
>  >    def foo; p :foo; end
>  >  end
>  >
>  >  module M
>  >    refine Array do
>  >      "".foo  # => OK
>  >    end
>  >  end
>  >end
>  >
>  >using R::M
>  > "".foo  # => NG

This is incredibly confusing to me. Why are the String refinements active within the refine Array block? That module:

* Is not within the refine String block
* Is not within a file that uses the String refinement
* Does not refine String

Why can it see the String refinements even though it's not in a "using" file and not within a refine String block?

>  I meant included module will provide refinement of combination of including
>  module(s) and the module itself.

This seems mostly reasonable, since modules that include modules carry all those modules with them to the eventual include site. So using basically considers the entire hierarchy of modules.

>  |For example, how should the following code behave?
>  |
>  |  module R1
>  |    refine String do
>  |      def bar
>  |        p :bar
>  |      end
>  |    end
>  |  end
>  |
>  |  module R2
>  |    include R1
>  |    refine String do
>  |      def foo
>  |        p :foo
>  |      end
>  |    end
>  |    "".foo
>  |    "".bar
>  |  end
>  
>  Since all calls of "".foo and "".bar are outside of refine blocks,
>  they should raise NoMethodError.  But R2 should provide refinement to
>  add method #bar and #foo to String class.

More interesting, given the above modules... I assume this would work:

#some file that's loaded the above refinements
using R2

"".foo # => OK
"".bar # => OK

>  |Finally, how super in refinements should behave in the new spec?
>  
>  Refinements should come before normal methods, so super in the normal
>  method will not see a refined method, and super in the refined method
>  will see a normal method (or other refined method if refinements are
>  stacked).

By stacking, I assume you mean something like this:

class String
  def bar; p :base; end
end

module M1
  refine String do
    def bar; p :m1; super end
  end
end

module M2
  refine String do
    def bar; p :m2; super; end
  end
end

using M1
using M2

"".bar # => should print :m2, :m1, :base

Correct?

My idea of *actually* putting refinements into the hierarchy seems like it might fit this best, rather than searching two hierarchies. Will have to think about it more.

>  Any more questions?

Yes, lots! :)

* Will we make more methods have special access to the caller's frame to support refinements? I'm speaking here of modifications to send, method reflection, to_proc, and so on. Of these, send sorta has access to caller frame, but it's unspecified (send :binding behaves differently on different impls). The reflection methods (method, instance_method, ...) and to_proc do not currently have access to caller's frame, and would have to be special-cased (and in JRuby that would force deoptimization of code that calls them to ensure we have a frame available).  I would argue that *none* of these methods should see the effects of refinements, because they are not defined within a refined file or scope. Making them see refinements extends refined effects down-stack in unpredictable ways.

* Questions about about the scoping of refinements in seemingly unrelated refine blocks.

* Performance expectations. Is performance being completely ignored here, or shall we set some goals for the implementation? I appreciate your desire to make Ruby more expressive, but that doesn't pay the bills at the end of the day if refined calls are 100x slower than regular calls. Some consideration of performance needs to be made up front. I would propose that unless refined calls can be made exactly the same speed as unrefined calls, they should not be included. We'd essentially be adding a file-scoped feature that hurts performance of all calls in that file. Expressivity doesn't trump slowing an entire system down because of a single call made at the top level of a file.

I'm glad to see refinements being reduced in scope, but we still have a lot to talk through. I share others' concerns about this feature not being settled just a couple months before 2.0 is supposed to be released, and at this point I'd still rather see it delayed to 2.1 so we can work through all the edges. I do not yet have a clear picture in my head of how refinements are supposed to be structured, and will have to reboot the understanding I did have based on recent updates.

I will try to modify my refinements implementation to work according to the new specification and see how it feels, implementation-wise.

FWIW, I made an improvement to JRuby 1.7.2 that makes the calling scope (the static part where cref and refinements live) available to all methods, even when scope/frame have been optimized away. It may make it possible to implement refinements without reducing the number of optimizations we do.

To others on this thread: I'd really like to hear more substantive input on the feature, rather than just "please don't do this, it's bad, I don't like it, it's too late, wah wah." If you have a specific aspect you don't like, discuss that. If you don't like the feature in toto, explain why. Special pleading for it to be removed does not further the conversation.
----------------------------------------
Feature #4085: Refinements and nested methods
https://bugs.ruby-lang.org/issues/4085#change-34162

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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