Forum: Ruby-core Refinements and nested methods

Issue #4085 has been updated by matz (Yukihiro Matsumoto).


Since there still remain undefined corner case behavior in refinements, 
and the time is running out, I decided not to introduce full refinement 
for Ruby 2.0. The limited Ruby 2.0 refinement spec will be:

* refinements are file scope
* only top-level "using" is available
* no module scope refinement
* no refinement inheritance
* module_eval do not introduce refinement (even for string args)

In addition, Module#include should add refinements to included modules, 
e.g.

  module R1
    refine String do
      def bar
        p :bar
      end
    end
  end

  module R2
    include R1
    refine String do
      def foo
        p :foo
      end
    end
  end

  using R2
  "".foo
  "".bar

  module R1
    refine String do
      def bar; p :bar end
    end
  end

  module R2
    include R1
    refine String do
      def foo; p :foo end
    end
  end

  using R2
  "".foo
  "".bar  # does not work now

You can treat top-level "using" as soft-keyword, as long as it does not 
change the behavior (but performance).

Matz.


----------------------------------------
Feature #4085: Refinements and nested methods
https://bugs.ruby-lang.org/issues/4085#change-34117

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

> Since there still remain undefined corner case behavior in refinements, and the 
time is running out, I decided not to introduce full refinement for Ruby 2.0. The 
limited Ruby 2.0 refinement spec will be:
>
> * refinements are file scope
> * only top-level "using" is available
> * no module scope refinement
> * no refinement inheritance
> * module_eval do not introduce refinement (even for string args)

While this removes a number of potential causes of problems we're now
stuck with a feature-set that can not cover many of the originally
discussed use-cases.

And to support the restricted feature set we already have disagreements
where refinements should be injected in the method hierarchy. What is
labled as a "design decision" aren't even edge cases anymore. They're
essential behavior of a new feature decided without much discussion or
analysis in the context of potential uses.

For DSLs we already have BasicObject + method_missing + instance_eval,
so only ruby literals may need some sugar added to make the DSL really
fluent. But if you already have all the instance_eval magic going then
you don't really want to require people to pepper their code with
"using" just so they can use your magical DSL.

For patching broken/incompatible code Module.prepend is much better
anyway since the breakage may occur in 3rd party code where you can't
use "using" anyway.

So with what does this leave us? String.camelize and 2.days.ago? Those
are supposed to be convenience methods.

If your files end up with a header of

   using "EnumeratorExtensions", "ActiveSupport::ClassNameConversions",
"MyApplication::DateHelpers", "SomeGem::HashExtensions",
"MyApplication::ActiveRecordExtensions", .......

That's not convenient at all anymore.


Personally I wouldn't want to use refinements as they are now. I would
love to have a powerful tool like pointcuts or Module.prepend in my
toolbox. Refinements wouldn't really qualify.


I'm getting the impression that refinements are getting rushed despite
being supposed to bring a completely new axis to the language along
which we can compose our applications. This shouldn't be happening in a
mature language. The whole way this is going right now feels wrong to 
me.

So I'm asking for two things: a) please consider removing refinements
from ruby 2.0. b) rethink how such big features should be designed in
the future.