Forum: Ruby-core Refinements and nested methods

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


matz (Yukihiro Matsumoto) wrote:
> 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:

I don't understand what do you mean by these constraints.  Let me ask 
some questions.

> * refinements are file scope
> * only top-level "using" is available
> * no module scope refinement

Do these constraints just mean that main.using is available, but 
Module#using is not?
How should the following code behave?

module R
  refine String do
    def foo; p :foo; end
  end
  "".foo # (a)
end
"".foo   # (b)

Currently, (a) prints :foo, and (b) raises a NoMethodError.
And, how about the following example, where a nested module is defined?

module R
  refine String do
    def foo; p :foo; end
  end

  module M
    "".foo
  end
  "".foo
end
"".foo

If the behavior in the new spec is the same as the current 
implementation,
I don't know well why Module#using should be removed.

> * no refinement inheritance
> * module_eval do not introduce refinement (even for string args)

I understand these.

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

This is very different from the current feature, so we need a discussion 
about it.
What does "add refinements" mean here?
There are two aspects about refinement addition.  They are defined in 
modules by Module#refine, and activated in certain scopes by using.
Does "to add refinements" mean to define (or inherit indirectly) 
refinements in modules, or to activate refinements in modules, or both 
of them?

For example, how should the following code behave?

  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
    "".foo
    "".bar
  end

Finally, how super in refinements should behave in the new spec?

----------------------------------------
Feature #4085: Refinements and nested methods
https://bugs.ruby-lang.org/issues/4085#change-34121

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

In message "Re: [ruby-core:50299] [ruby-trunk - Feature #4085] 
Refinements and nested methods"
    on Thu, 29 Nov 2012 15:02:03 +0900, "shugo (Shugo Maeda)" 
<redmine@ruby-lang.org> writes:

|> * refinements are file scope
|> * only top-level "using" is available
|> * no module scope refinement
|
|Do these constraints just mean that main.using is available, but Module#using is 
not?

Yes, only main.using should be available. No Module#using (for 2.0).

|How should the following code behave?
|
|module R
|  refine String do
|    def foo; p :foo; end
|  end
|  "".foo # (a)
|end
|"".foo   # (b)
|
|Currently, (a) prints :foo, and (b) raises a NoMethodError.

Refinements will be available only from:

* the scope where refinements are added by calling "using"
* or inside of refine blocks

Inside of refine blocks (not whole module scope) might be
controversial, but I think it's OK to restrict refinements there.  As
a result, both (a) and (b) raise NoMethodError.  But "".foo can be 
called
from within the refine block.

|And, how about the following example, where a nested module is defined?
|
|module R
|  refine String do
|    def foo; p :foo; end
|  end
|
|  module M
|    "".foo
|  end
|  "".foo
|end
|"".foo

Every "".foo in the above example should raise NoMethodError, because
they are outside of refine blocks.  I admit I've been less careful
about nested refinement modules.  For nested refinement modules, it
should behave as following:

>end
>
>using R::M
> "".foo  # => NG

|> In addition, Module#include should add refinements to included modules, e.g.
|
|This is very different from the current feature, so we need a discussion about 
it.
|What does "add refinements" mean here?
|There are two aspects about refinement addition.  They are defined in modules by 
Module#refine, and activated in certain scopes by using.
|Does "to add refinements" mean to define (or inherit indirectly) refinements in 
modules, or to activate refinements in modules, or both of them?

I meant included module will provide refinement of combination of 
including
module(s) and the module itself.

|For example, how should the following code behave?
|
|  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
|    "".foo
|    "".bar
|  end

Since all calls of "".foo and "".bar are outside of refine blocks,
they should raise NoMethodError.  But R2 should provide refinement to
add method #bar and #foo to String class.

|Finally, how super in refinements should behave in the new spec?

Refinements should come before normal methods, so super in the normal
method will not see a refined method, and super in the refined method
will see a normal method (or other refined method if refinements are
stacked).

The whole point is separation of defining refinements (for library
developers) and using refinements (for library users).

Any more questions?

              matz.