Forum: Ruby-core Refinements and nested methods

45196398e9685000d195ec626d477f0e?d=identicon&s=25 Thomas Sawyer (7rans)
on 2012-11-30 03:03
(Received via mailing list)
Issue #4085 has been updated by trans (Thomas Sawyer).


> |    include M1
> |    refine String do def foo; p :M2; super; end; end
> |  end
> |  using M2
> |  C.new.foo #=> ?
> |
> |I think it's better to just calls M2 and C, not M1, to simplify things.
> |super chain is too complex here.
>
> I was thinking of M2->M1->C, but M2->C is simpler and acceptable.

This can't be b/c then you can't refine a previous refinement. Thus it
breaks modularity (black box) principle. E.g. if I `require 'x.rb'` and
apply `using B`, it should not matter if x.rb is `using A` or not. (I
can explain that with a detail example if it is not clear enough).

----------------------------------------
Feature #4085: Refinements and nested methods
https://bugs.ruby-lang.org/issues/4085#change-34175

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
6738588a11b852833edf6aec90ef6fa3?d=identicon&s=25 Yukihiro Matsumoto (Guest)
on 2012-11-30 03:22
(Received via mailing list)
In message "Re: [ruby-core:50357] [ruby-trunk - Feature #4085]
Refinements and nested methods"
    on Fri, 30 Nov 2012 11:02:10 +0900, "trans (Thomas Sawyer)"
<transfire@gmail.com> writes:

|> I was thinking of M2->M1->C, but M2->C is simpler and acceptable.
|
|This can't be b/c then you can't refine a previous refinement. Thus it breaks
modularity (black box) principle. E.g. if I `require 'x.rb'` and apply `using 
B`,
it should not matter if x.rb is `using A` or not. (I can explain that with a
detail example if it is not clear enough).

You are right, by this spec you can refine a method only once in a
file.  But I don't understand how it breaks black box principle.
it does not change the behavior if required x.rb is 'using A' or not,
under the current spec.

              matz.
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