From: "headius (Charles Nutter)" <headius@...>
Date: 2012-11-14T05:23:52+09:00
Subject: [ruby-core:49319] [ruby-trunk - Feature #4085] Refinements and nested methods


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


Talking more with folks online about refinements, there's a lot of confusion about what they solve.

So, in one sense, refinements are to localize monkey-patching. But they don't actually localize it much better since they can apply at a distance to blocks (module_eval feature), and classes down-hierarchy.

Previously, all code determined what methods to call based solely on the target object's class hierarchy. Even with monkeypatches in place, we still have to look solely at the target class to determine what's being called.

With refinements, every piece of code everywhere in the system could potentially see refinements active whether there's a "using" clause near them or not. Blocks could be forced to call different methods at any time, normal code could see a superclass add a refinement and change all future calls. Refinements may prevent monkeypatches from affecting the entire runtime, but don't make it any easier to determine what methods will actually be called.

They also don't solve the monkeypatching problem in any way. Monkeypatches have been used for a few reasons:

* Adding methods to existing types, for DSL or fluent API purposes.

Refinements would limit the visibility of those methods, somewhat, but you can't tell without digging around both the target class hierarchy and the calling class hierarchy what methods will really be called.

* Replacing existing methods with "better" versions

Refinements would again limit the visibility of those changes, but ultimately result in some code calling one method and some code calling another, with no easy way to determine the code that will be called ahead of time.

It may be possible to address the technical issues of optimizing call sites with and without refinements, but I really don't feel like refinements are solving as many problems as they're going to create. I lament a future where I can't look at a piece of code and determine the methods it's calling solely based on the types it is calling against. It's going to be harder -- not easier -- to reason about code with refinements in play.
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Feature #4085: Refinements and nested methods
https://bugs.ruby-lang.org/issues/4085#change-32878

Author: shugo (Shugo Maeda)
Status: Assigned
Priority: Normal
Assignee: shugo (Shugo Maeda)
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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