Issue #4085 has been updated by trans (Thomas Sawyer).


I was reading this discussion (http://branch.com/b/rubyists-which-would-you-rather-have-in-ruby-2-0-0) about refinements, and read the last post by Magnus Holm (@judofyr) which said:

> I think refinements are useful for some specific tasks; String#camelize is *not* one of them.
> I see no real gain of using `"foo".camelize` over `StringUtils.camelize("foo")`.
>
> No, I think refinements should be used for DSLs. As @wycats mentioned: It's the difference
> between DataMapper.not(:age => 12) and `:age.not => 12`. Or `5.days.ago` instead
> of `DateUtilts.now.subtract(:days => 5)`.
>
> And in that context I think that *lexical* refinements makes a whole lot more sense than
> dynamic refinements; both in terms of debugging and in terms of sanity.

For a while I too was thinking that same thing. But now it seems to me that perhaps this kind of DSL is just bad API design --in particular the whole idea of adding a bunch of methods to Symbol class.

For example, something like `:age.not => 12` could be written as a block DSL instead as `{ age != 12 }`. That's so much sexier anyway.

As for something like `5.days.ago`, I agree with Steve Klabnik who calls such cases more of a "social" problem. It is something that's common enough that it would be better if Ruby had a concept of Duration built-in and some convenient conversion methods on Numeric. At worse there could be single entry point like `5.calendar.days.ago` or maybe `5.th(:day).ago`. Certainly we don't need something as course as `DateUtilts.now.subtract(:days => 5)`, but we could still do something reasonable without a bunch of refinements.

So I guess my point is that refinements are not really even addressing a "20%" problem, it seems more like a "1%" problem. And as cool as they seem, I am not so sure that's enough.

Again, I'll mention that I am a bit afraid of what might happen if refinements become popular. Imagine a library with dozens of various refinements on all the core classes. Might we start seeing DSLs like: `:batter.count(1.ball && 2.strikes)`.



----------------------------------------
Feature #4085: Refinements and nested methods
https://bugs.ruby-lang.org/issues/4085#change-33871

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



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