From: "myronmarston (Myron Marston)" Date: 2012-11-30T00:41:31+09:00 Subject: [ruby-core:50331] [ruby-trunk - Feature #4085] Refinements and nested methods Issue #4085 has been updated by myronmarston (Myron Marston). I find refinements to be a _very_ interesting idea, but, as with many others, it concerns me that there aren't rubyspecs behind it, there's still undefined edge cases, the main language maintainers are still discussing how it should work, and the existing implementation has a perf impact. In the past, I've heard RSpec used as a main example of a library that could really benefit from refinements. As of yesterday, I'm the lead maintainer of RSpec, and I'm doubtful whether or not we'll ever use them. Given the fact that we need to maintain support for 1.8.7, 1.9.2 and 1.9.3 for as long as its common for gem authors to support those versions (since we'd like RSpec to be useable to test all the commonly supported rubies), we won't be in a position to use refinements for many years. In the meantime, we've already started significantly reducing the number of monkey patches RSpec does to Object in the 2.x releases, and I'm hoping to reduce this even more for 3.0. Really, I think a feature like refinements needs to see some *actual production usage* before being included in the language. It needs a long vetting period. I think a key part of rails' success is the fact that it was extracted from a production app, rather than being built on its own first. I haven't read this whole thread (it's huge, and it's hard to find the time to read every comment), so I have no idea if this has been discussed or not...but here's an idea I just had: For 2.0, extract refinements out of the core language into a c-extension gem. Ask the community to give refinements a shot. Encourage actual production usage. Learn from real-world usage, and clarify the spec before considering putting them back in the core language. Of course, this idea depends upon it being doable to extract refinements into a gem; given the affect they have at the core language level, that may not be doable. But it would be great to have some way for refinements to be released so people could start trying them *without* putting them directly in MRI -- that gives the language designers and maintainers time to learn from real world usage and refine refinements (sorry for the bad pun). Myron ---------------------------------------- Feature #4085: Refinements and nested methods https://bugs.ruby-lang.org/issues/4085#change-34153 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 -- http://bugs.ruby-lang.org/