Forum: Ruby-core Refinements and nested methods

2abdb50caf0dc5b510330f68b02db8e4?d=identicon&s=25 rosenfeld (Rodrigo Rosenfeld Rosas) (Guest)
on 2012-11-20 12:26
(Received via mailing list)
Issue #4085 has been updated by rosenfeld (Rodrigo Rosenfeld Rosas).

shugo (Shugo Maeda) wrote:
> Some people seem to suspect that code using refinements is difficult to debug,
but reflection APIs may be useful to debug such code.

I don't think the big problem is debugging, but readability. This is my
own definition of readability: the longer it takes for one to understand
some code, the less readable it is. In that sense, refinements in
libraries seem even less readable than refinements in application code.

Consider someone new to Ruby reading a Rails code like
"some_string.camelize". He could look for camelize in String class RDoc
and he wouldn't find it there. He would be forced to use the reflection
API to understand where is that method coming from. This reduces
readability as the developer now needs an extra step (time) to figure
out where that method is coming from. Looking at the API is quick.
Debugging or using the reflection API is not that quick. That is the
same problem I have with Monkey Patches. They reduce readability. It is
even worse when it overrides some built-in method and change its

That is the same reason I don't add extensions of my own to core classes
(like aliasing each_with_object to a shorter name, etc). It makes it
harder for others in the team to read the application code.

I'm pretty sure that once refinements are included in final 2.0.0 people
will start using it just because they want to use the new fancy feature
and not because they really feel its need. This is what probably
happened when DHH first introduced dynamic finders in ActiveRecord in my
opinion. I believe he found it fantastic the method_missing feature and
decided to use it just because he could. There was no real need for
that. And people keep saying that it is ok to use monkey patches and
method_missing at will and that Ruby even encourages that practice or
otherwise those features wouldn't exist. People build some culture over
what is Ruby best practices and what is not. I remember that someone
from the Rails core team judging my patch some years ago stating that I
shouldn't use "is_a?" because the Ruby way is to use duck-typing. Even
so I really wanted to test for the specific class instead of just asking
if the object responds to some method. It was much more readable to use
  "is_a?" in that context.

I'm afraid that once refinements are possible in Ruby they will be
immediately abused just because they are fancy and it will take years
for libraries to start to avoid them because they are no longer fancy
(like what happened to ActiveRecord removing the dynamic finders just
now, years after it has been introduced to AR).

I know this is hard to balance. People moved from other languages to
Ruby because Ruby was a more powerful language. But that is not the
single reason. It was also more readable. But a feature like this one
has its tradeoffs. It makes Ruby more powerful, by reducing conflicts
that might be created by conflicting versions of monkey patches. But at
the cost of both performance (which I think is the least problem here)
and readability.

The worst part for me is that even if I opt out for using refinements
myself, I'll still have to live with it and create tons of checks when
debugging code and trying to understand others'
(libraries/frameworks/applications) code. I realize this issue is not
introduced by this feature as monkey patches have the same effect. But
the problem this feature introduces is that it becomes even harder to
read code once refinements are possible.

For instance, with monkey patches, if I just make sure I load/require
all files in the same order, I could write a code using the reflection
API to understand where a method is coming from. But now this won't
suffice anymore because the same method could be defined elsewhere when
inside another context. If that other context is not easily
triggered/reproducible than it gets even hard to try to understand why
that special condition is not working under production, for instance.
Imagine yourself trying to fix a bug caused by some race-condition that
you can't always replicate. Usually some code inspection is all that you
get left to work on. But once refinements are possible, inspecting some
code becomes so much more difficult to perform :(

Then, the real question is: what is most important? Powerful or
readability/performance? We can't get both with this feature.
Feature #4085: Refinements and nested methods

Author: shugo (Shugo Maeda)
Status: Assigned
Priority: Normal
Assignee: matz (Yukihiro Matsumoto)
Category: core
Target version: 2.0.0

 As I said at RubyConf 2010, I'd like to propose a new features called

 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

 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

 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

   f = #=> (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"

     def baz

   module FooExt
     refine Foo do
       def bar
         puts "FooExt#bar"

   module Quux
     using FooExt

     foo =  # => FooExt#bar
     foo.baz  # => Foo#bar

 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

   class Foo
     # MathN is enabled in a reopened definition.
     p 1 / 2  #=> (1/2)

   class Bar < Foo
     # MathN is enabled in a subclass definition.
     p 1 / 2  #=> (1/2)

 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
   class B
     using MathN
   MathN.module_eval do
     p 1 / 2  #=> (1/2)
   A.module_eval do
     p 1 / 2  #=> (1/2)
   B.class_eval do
     p 1 / 2  #=> (1/2)
   end do
     p 1 / 2  #=> (1/2)

 Besides refinements, I'd like to propose new behavior of nested
 Currently, the scope of a nested method is not closed in the outer

   def foo
     def bar
       puts "bar"
   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 = {
       refine klass do
         def bar
           puts "bar"
     using m
   foo  #=> bar
   bar  #=> NoMethodError

 The attached patch is based on SVN trunk r29837.
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