From: "headius (Charles Nutter)" <headius@...>
Date: 2012-12-01T04:41:30+09:00
Subject: [ruby-core:50410] [ruby-trunk - Feature #4085] Refinements and nested methods


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


Anonymous wrote:
>  From usability perspective, all retrospective methods e.g. respond_to?
>  methods etc. should reflect refinements. But for 2.0, I don't make
>  them check refinements, because of performance and complexity.  It
>  should be issue of future version.

respond_to? brings up a really good point: there's lots of methods that might need special refinement care...but I think it makes things more confusing rather than less.

Let's take the respond_to? example. You want respond_to? to reflect refinements. That seems reasonable on the surface, even though respond_to? is not refined itself. The first peculiarity there is that you could no longer wrap respond_to?, respond_to_missing?, method, instance_method, and so on, because wrapping them would break their visibility to refinements (due to the intervening unrefined Ruby frame). We'd be reducing the metaprogrammability of many, many core methods.

And then there's methods that *call* respond_to? (or coercion methods like to_s). Example:

class X; end

module M1
  refine X
    def to_path; '/tmp'; end
  end
end

using M1

File.open(X.new) # ????

File.open checks respond_to?(:to_path) and if that succeeds it calls to_path. But the above code will never work unless File.open is also made refinement-aware.

I think this is a pretty significant problem, and it shows how much more limited refinements will actually be. The bottom line is that making any core methods reflect refinements may be *more* confusing, because only direct invocations will work...not wrapped invocations, called-method invocations, or double-dispatched invocations.

Again it may be good to look at C# extension methods, which are not reflected: http://stackoverflow.com/questions/299515/c-sharp-reflection-to-identify-extension-methods

More and more I see the only value of refinements as providing extension methods for specific classes in specific scopes. If we want reflective access, we should provide something like C# that allows getting the available refined methods and a mechanism that returns the current active refinements. Users can figure out what they need from there without special-casing a whole bunch of core methods.

class Module
  def refined_methods ...
  def refined_instance_methods ...
end

module Kernel
  def active_refinements ...
end

More coming...
----------------------------------------
Feature #4085: Refinements and nested methods
https://bugs.ruby-lang.org/issues/4085#change-34236

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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