From: "headius (Charles Nutter)" <headius@...>
Date: 2012-11-22T05:46:28+09:00
Subject: [ruby-core:49829] [ruby-trunk - Feature #4085] Refinements and nested methods


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


I would also vote to remove refinements from 2.0 features, perhaps for reinclusion in 2.1. The various points made about lack of clear specification, lack of time to experiment, lack of clarity on the extent of damage/risk, and lack of time for other implementers to fully implement and explore the feature all point toward this being too much, too late in 2.0's dev cycle...and I believe it is too close to 2.0's release to shove the features in.

That said, I will say I appreciate the reduction in scope. Having refinements only searched via lexical enclosures makes the feature much simpler to implement and much easier to understand in real code. To help the process of fleshing out the feature, I have implemented a large part of the reduced refinements feature for JRuby on the refinements branch: https://github.com/jruby/jruby/tree/refinements

Here are my notes on the current JRuby implementation:

* Only the interpreter is supported for now. Compiler support will require a rework of how we access the scope.

* Much of the determination of whether refinements are active can be static. I set a flag in StaticScope after any call to "using" that flags subsequent calls as refined. This narrows refinement impact to calls following "using".

* I have no strong preference as to whether "refine" additions after a "using" call should be expressed; if they are to be expressed, it means holding a reference to the refinement holder module in the cref; if they are not, it means copying them at the moment of the "using" call.

* Reflective methods (method, instance_method, etc) will have to be special-cased in the refined call site, so that the refinements are looked up. We do not want to have to propagate refinements through to the default implementation of those methods.

* My current implementation caches refinements at the call site based on a global token, incremented whenever a refinement change happens. This allows refined calls to be equivalent performance to unrefined calls in most cases, but it ignores all other invalidation mechanisms (hierarchy changes, etc).

* I am not currently searching modules included into modules for refinements.

* super is not implemented; it is not clear to me how to implement it simply/efficiently in JRuby.

---

I believe we can implement the lexical-only version with reasonable efficiency. My implementation still follows your basic structure, putting refinements on cref and using anonymous modules to hold them. As mentioned in the notes above, I do not have the special behavior for reflection or super implemented; several of the missing features will be more complicated to complete in JRuby due to the way we optimize code. I will also need to rework the way we handle scoping in JRuby's compiler to efficiently access the cref scope without requiring a full frame, but so far I believe everything is doable.

I still vote to delay adding refinements until after 2.1. It feels very rushed now.
----------------------------------------
Feature #4085: Refinements and nested methods
https://bugs.ruby-lang.org/issues/4085#change-33413

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



-- 
http://bugs.ruby-lang.org/