Forum: Ruby-core Refinements and nested methods

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


Well, I have some bad news.

I have spent some time trying to find a reasonable way to implement 
refinements in JRuby, and without reducing the feature set it's simply 
not possible to do without global (and sometimes terrible) impact to 
general application performance.

At this point I'm largely of the opinion that pure-lexical, syntactical 
refinements are the way to go. And there are several reasons for it:

* Dynamic refinements have far-reaching impact, both peformance-wise and 
"understandability" of the code. It's both hard (or impossible) to 
optimize and hard (or impossible) to reason about.
* Syntactic/lexical refinements are nearly self-explanatory in code. 
Currently, when you look at a piece of code with method calls (and 
constant lookup, as well), you can reason about it in terms of the 
enclosing classes/modules and basically know what it will call. 
Monkeypatching can obscure the eventual method called, but every piece 
of code everywhere will still call the same method. With dynamic 
refinements, it's impossible to look at a piece of code and the classes 
involved and know what method will be called, because it can change 
arbitrarily at runtime.
* The current refinements are poorly specified and have only been 
explored in a very limited way. This is of *great* concern to me. There 
are a huge number of potential edge cases, ranging from abuse of the 
module_eval feature to reopening existing refinements (which essentially 
just makes monkeypatching harder to discover), and implementation-wise 
there has not been enough exploration of how it will affect current and 
future performance of Ruby. We need more time to define what refinements 
should do in terms of what users want and what's reasonable from a 
language-design perspective.

I would support the idea of pure lexical/syntactic refinements of the 
following form, but I don't see a way to support the features of the 
current refinements implementation reasonably on any VM.

module Foo
  class Quux
    using Bar, Baz
      def blah
         'abc'.efg # refined
      end
    end

    def blah2
      'asdf'.qwer # unrefined
    end
  end
end
----------------------------------------
Feature #4085: Refinements and nested methods
https://bugs.ruby-lang.org/issues/4085#change-32829

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