From: "shugo (Shugo Maeda)" <redmine@...>
Date: 2012-11-26T18:34:09+09:00
Subject: [ruby-core:50154] [ruby-trunk - Feature #4085] Refinements and nested methods


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


headius (Charles Nutter) wrote:
> ko1's suggestion, as I understand it, was to add a flag to the method table (or method entry) of a refined class/method as a trigger for the call site to search refinements. While writing my blog post, I started to type the sentence "the methods defined in the refinement do not actually go on the class in question", and then I realized: why not?
> 
> Currently, Ruby implementations structure the method table as a simple map from names to method bodies. If instead the method table was a map from names to collections of methods, we could use that to choose the appropriate method for a given context.
> 
> So, for code like this:
> 
> module X
>   refine String do
>     def upcase; downcase; end
>   end
> end
> 
> String's method table would contain an entry like this:
> 
> {:upcase => {
>   :default => <builtin upcase>,
>   X => <upcase patched>}
> }
> 
> Method lookup would then proceed as normal in all situations. The result of lookup would be a table mapping refinements to methods with a default entry if the method is defined directly on String.

It's an interesting idea.
How does method lookup work if multiple modules are used by using?

module Z
  using X
  using Y
  "foo".upcase
end

Are both X and Y used as a key of the table in the reverse order they are used by using?

And, how does super work?

> I admit I am a bit reluctant to suggest this, because I still have concerns about the feature itself. But it would be possible for call sites to only need a reference to their calling scope (determined at parse time) to implement dynamic refinements without severe impact to normal code. Dynamic refinements, as in module_eval, would work by simply invalidating the call sites they contain.

FYI, in my new implementation (http://shugo.net/tmp/refinement_fix_1119.diff), refined methods are not stored in inline cache, so there's no need to invalidate inline cache for module_eval.
Instead, refined method invocations are slower than the implementation in the trunk HEAD.

> In any case, I would really like more time for this dialog to continue. If we push refinements into Ruby in their current form, we're not giving adequate time to flesh out the edge cases. If we push a partial implementation now, we may be making a future implementation harder and we would not be protecting ourselves from mistakes. I want to work with you to find a definition and implementation of refinements that meets requirements without punishing future Rubyists.

I'm starting to think it's not good to rush to introduce Refinements as an official feature.
What do you think of introducing Refinements as an experimental feature as Endoh-san suggested?
I don't know what does Endoh-san mean by "an experimental feature", but it may require an explicit compile option or a runtime option (e.g., require "refinements" like continuation) to enable it.  If Refinements are enabled, warning should be shown not to make the current Refinements de-facto standard.

> I also must apologize for not joining the dialog sooner. This bug was filed in 2010, and the current refinements implementation was pushed to master a few months ago. We should have started discussing a long time ago.

I should also have warned people to think of Refinements sooner.  Anyway, thanks for your comments.

----------------------------------------
Feature #4085: Refinements and nested methods
https://bugs.ruby-lang.org/issues/4085#change-33946

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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