From: "headius (Charles Nutter)" <headius@...>
Date: 2012-12-08T04:36:25+09:00
Subject: [ruby-core:50671] [ruby-trunk - Feature #4085] Refinements and nested methods


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


rosenfeld (Rodrigo Rosenfeld Rosas) wrote:
> So, by using your definition of refinements I'd need to separate them by file so that I could use "using Sequel::SymbolExtensions" in a file and "using Squeel::SymbolExtensions" in another file. And I wouldn't ever be able to use both in a single method.

Is this a use case we want to support? Being able to use multiple different monkey-patches in the same method body? I am skeptical.

> The problem is not that I don't understand it. I do. I just don't find its behavior consistent.
> 
> Ruby is a good language (not good enough, though) and my preferred one but it has lots of drawbacks and I'd really love to see its drawbacks being fixed (lack of proper thread support in MRI is the main one by the way). That is why I set up some time everyday to read all messages in the ruby-core mailing list and say my opinions on them when I find them relevant.
> 
> For this particular issue I'm just asking for the reasoning behind your design decisions so that I can understand your point of view before I can try to persuade you to go in another direction. But you haven't explained any reasons in your previous message. So I don't know how you expect me to understand the rule or to find it consistent if I don't understand the problem you're trying to solve. It would be helpful if you could provide some real-world example that you find refinements would help implementing.
> 
> Also, I didn't learn anything from ActiveSupport so I have no idea what you're talking about when you say "we don't care if methods are added to the existing classes". Particularly, I do care, specially when your project grows and you don't know what libraries added new methods to existing classes of if some built-in method has been overriden. It is pretty likely that conflicts will arise as the project grows and lots of libraries are used.
> 
> I value open classes and monkey patching but not as something to use as your daily programming tool. It should be used to fix some library until it is fixed main-stream in my opinion. Abusing from such language feature is not a good programming practice in any language.
> 
> I'm pretty sure others will agree with me but since Ruby doesn't provide library authors other options (like local refinements) they have a tradeoff and often they'll opt for monkey patching native classes (like symbols) even when they agree that those methods should exist only in certain contexts but Ruby doesn't provide them any feature to allow this to happen so they end up with the monkey patch approach.
> 
> This situation could be greatly improved if Ruby provided some feature like local refinements.

Patches accepted? :-)

Honestly, there are certain features that are so difficult to implement efficiently that no matter how useful they may be they're not worth the cost. I believe local, non-lexical refinements fall into this category due to the complexity of constantly checking whether a refinement is active
----------------------------------------
Feature #4085: Refinements and nested methods
https://bugs.ruby-lang.org/issues/4085#change-34519

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/