Forum: Ruby-core Refinements and nested methods

Issue #4085 has been updated by headius (Charles Nutter).


rosenfeld: Yes, I am arguing that same case. I believe refinements 
should only be active for code that appears within a refined context. My 
example from earlier:

class Foo < SomeParent
  def bar(str)
    str.upcase # unrefined
  end

  using StringRefinement
    def baz(str)
      str.camlize # refined
    end
  end
end

There are implementation reasons why this is simpler, but the more 
important reasons are readability, understandability of the code. You 
know exactly whose methods will be called in both cases -- String's in 
the bar() body and StringRefinement's or String's in the baz() body -- 
and there's no question whether refinements are active for a given call. 
Compare that to the following code:

class Foo < SomeParent
  def bar(str)
    str.upcase
  end

  def baz(str)
    str.camelize
  end
end

What methods are being called? Where are they coming from? You can't 
know, since you need more information that the type of object that str 
is. You need to know whether Foo has previously had refinements applied, 
whether SomeParent previously had refinements applied, whether its 
parents previously had refinements applied...you need to know what those 
refinements are and whether they affect String methods...and you need to 
know whether any of the methods you are calling have been refined.

EVERY PIECE OF CODE in a given system now forces users to understand 
BOTH the target class being called AND the hierarchy of code surrounding 
the call. That's not simpler, it's more complicated...and it affects the 
readability of ALL CODE.

And then there's this:

class Foo < SomeParent
  def baz(str)
    ary.map {|name| str.camelize + name}
  end
end

In this case, you have to check even more places for refinements to know 
what methods will be called:

* Foo may have been previously refined. You must look for all reopenings 
of Foo to know what will be called.
* SomeParent or its parents may have been previously refined. You must 
look for all reopenings of SomeParent and its parents.
* The map method may force refinements on the block. you must look for 
all implementations of map() that might be called here to see if they 
force refinements into the block.

This is supposed to be simpler?
----------------------------------------
Feature #4085: Refinements and nested methods
https://bugs.ruby-lang.org/issues/4085#change-32879

Author: shugo (Shugo Maeda)
Status: Assigned
Priority: Normal
Assignee: shugo (Shugo Maeda)
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

On Wed, Nov 14, 2012 at 05:38:12AM +0900, headius (Charles Nutter) 
wrote:

[snip]

> * Foo may have been previously refined. You must look for all reopenings of Foo 
to know what will be called.
> * SomeParent or its parents may have been previously refined. You must look for 
all reopenings of SomeParent and its parents.
> * The map method may force refinements on the block. you must look for all 
implementations of map() that might be called here to see if they force 
refinements into the block.
>
> This is supposed to be simpler?

I have to agree.  It seems like this would be *much* more difficult to
debug than if `camelize` is just monkey patched on to String.

This code:

  class Foo < SomeParent
    def baz(str)
      cached = str.camelize
      ary.map {|name| cached + name}
    end
  end

Could have a completely different meaning than this code:

  class Foo < SomeParent
    def baz(str)
      ary.map {|name| str.camelize + name}
    end
  end

That seems extremely bad.

Perhaps refinements should be scoped per-gem, rather than any arbitrary
"using" delimitation. Seems to me, that is generally the level at which 
we
care about them.

Would that simplify implementation and comprehensibility of usage to
something more manageable?


On Wed, Nov 14, 2012 at 1:35 PM, Aaron Patterson
<tenderlove@ruby-lang.org>wrote:

> > end
> refinements into the block.
>       cached = str.camelize
>   end
>
> That seems extremely bad.
>
> --
> Aaron Patterson
> http://tenderlovemaking.com/
>
>


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