From: "shugo (Shugo Maeda)" <redmine@...>
Date: 2012-11-21T15:15:50+09:00
Subject: [ruby-core:49799] [ruby-trunk - Feature #4085] Refinements and nested methods


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


The8472 (Aaron G) wrote:
>  Therefore I think that class inheritance should be removed. And if it 
>  gets replaced in the future then it should be with submodule based 
>  inheritance.

I'll remove it if permission granted by Matz.

>  For now people can use Module.extended/.included if they really want to 
>  add refinement inheritance themselves.

Currently this wouldn't work because you cannot get the caller context in these hooks.

>  > B. refinement activation for reopened module definitions
>  > C. refinement activation for the string version of module_eval/instance_eval
>  > D. refinement activation for the block version of module_eval/instance_eval
>  
>  I don't feel strongly about those, but if the module_eval performance 
>  really has such a big issue as headius asserts then it might be better 
>  to postpone it until a solution has been found.

A solution has been found at least in CRuby.
I'm waiting for ko1's review.

>  Probably the safest approach for now would be to use the source 
>  refinement scope (which is quasi-static) for module_eval by default and 
>  add a way to use the target scope (or an explicit scope) later on as 
>  needed. If there is any performance impact it would restricted to the 
>  target-scoped procs.

Do you mean that a new option of module_eval should be introduced?
For example,

  Foo.module_eval { # use refinements in the current context }
  Foo.module_eval(using_refinements: true) { # use refinements in the receiver }

>  What about cases like
>  
>     module SomeExt
>       refine String do
>         def bar
>         end
>       end
>     end
>  
>     class Foo
>       using SomeExt
>  
>       def self.test1
>         "".tap(&:bar)
>       end
>  
>       def self.test2
>         "".tap{|f| f.bar}
>       end
>     end
>  
>  
>  String.bar is only visible inside Foo, but in test1 the Proc is created 
>  in .to_proc of Symbol, i.e. on a different stack frame, which shouldn't 
>  be able to see bar due to the scoping. Which leads to counter-intuitive 
>  results.

Originally, String#bar was not visible in the Proc created by Symbol#to_proc.
But I've changed it because Matz asked to do.  I think the current behavior
is not consistent, but useful.

If Symbol#to_proc were written in Ruby, it would be impossible, but
Symbol#to_proc is written in C.  There are some such special methods.
For example, Module.nesting returns the module nesting information in the
caller context.  Module#using also affects the caller context.

----------------------------------------
Feature #4085: Refinements and nested methods
https://bugs.ruby-lang.org/issues/4085#change-33380

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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