Forum: Ruby-core Refinements and nested methods

Issue #4085 has been updated by rosenfeld (Rodrigo Rosenfeld Rosas).


Look, refinements could probably save Ruby from many drawbacks that 
currently exist. But I don't really understand what problem you're 
trying to solve with your definition of refinements.

Currently there are some gems that support the concept of extending 
Symbols so that you can use it like in the example above. The problem is 
that currently you can't use both Sequel and Squeel gems because both 
override the same symbol methods.

So, by using your definition of refinements I'd need to separate them by 
file so that I could use "using Sequel::SymbolExtensions" in a file and 
"using Squeel::SymbolExtensions" in another file. And I wouldn't never 
be able to use both in a single method.

It is not a problem that I don't understand it. I do. I just don't find 
its behavior consistent.

Ruby is a good language (not good enough, though) and my preferred one 
but it has lots of drawbacks and I'd really love to see its drawbacks 
being fixed (lack of proper thread support in MRI is the main one by the 
way). That is why I set up some time everyday to read all messages in 
the ruby-core mailing list and say my opinions on them when I find it 
relevant.

For this particular issue I'm just asking for the reasoning behind your 
design decisions so that I can understand your point of view before I 
can try to persuade you to go in another direction. But you haven't 
explained any reasons in your previous message. So I don't know how you 
expect me to understand the rule or to find it consistent if I don't 
understand the problem you're trying to solve. It would be helpful if 
you could provide some real-world example that you find refinements 
would help implementing.

Also, I didn't learn anything from ActiveSupport so I have no idea what 
you're talking about when you say "we don't care if methods are added to 
the existing classes". Particularly, I do care, specially when your 
project grows and you don't know what libraries added new methods to 
existing classes of if some built-in method has been overriden. It is 
pretty likely that conflicts will arise as the project grows and lots of 
libraries are used.

I value open classes and monkey patching but not as something to use as 
your daily programming tool. It should be used to fix some library until 
it is fixed main-stream in my opinion. Abusing from such language 
feature is not a good programming practice in any language.

I'm pretty sure others will agree with me but since Ruby doesn't provide 
library authors other options (like local refinements) they have a 
tradeoff and often they'll opt for monkey patching native classes (like 
symbols) even when they agree that those methods should exist only in 
certain contexts but Ruby doesn't provide them any feature to allow this 
to happen so they end up with the monkey patch approach.

This situation could be greatly improved if Ruby provided some feature 
like local refinements.
----------------------------------------
Feature #4085: Refinements and nested methods
https://bugs.ruby-lang.org/issues/4085#change-34484

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

On 06.12.2012 17:01, rosenfeld (Rodrigo Rosenfeld Rosas) wrote:
> The problem is that currently you can't use both Sequel and Squeel gems because 
both override the same symbol methods.

That's not necessarily true. Squeel supports the extended-symbol as
legacy syntax for metawhere support, which you can turn off at load
time. It also provides a far better strategy:

Building an AST via BasicObject + instance_eval + method missing.

That way practically anything that's not a local variable can become a
DSL-keyword.

Date-patching to fixnums could be easily circumvented in DSLs too by
doing something like

   dsl{in(15).days; after(15).days}


So really. DSLs should not be the issue here, if people would actually
design them properly.


Only library-level extensions to Strings/Arrays/Hash etc. such as those
of ActiveSupport should be considered a use-case for refinements, since
you don't use them in a very localized scope. You actually use them
throughout your whole library and don't want to be bothered to include
something into every file just to be able to use your utility method.

Em 06-12-2012 23:17, The 8472 escreveu:
> That way practically anything that's not a local variable can become a
>
>
> Only library-level extensions to Strings/Arrays/Hash etc. such as
> those of ActiveSupport should be considered a use-case for
> refinements, since you don't use them in a very localized scope. You
> actually use them throughout your whole library and don't want to be
> bothered to include something into every file just to be able to use
> your utility method.
>

That was just an example justifying that local refinements can be quite
useful and that multiple libraries may want to override (or add) the
same methods to some core class but with different behaviors (thus
creating conflicts). I don't really have a need for Squeel (or
MetaWhere) and even for Sequel I disable all core extensions (Sequel
also provides this option) since I don't want any library to be adding
(or modifying) methods in core classes:

http://sequel.rubyforge.org/rdoc/files/doc/core_ex...

but "where(:column.like('A%'))" reads better than "where(Sequel.like
:column, 'A%')" and I always alias Sequel as S so that I can write
"where(S.like :column, 'A%')".

I'm just saying that it would be great if we could support something
like "where{:column.like 'A%'}" without monkey patching symbols in all
contexts. But at the same time I don't want Ruby to support this because
it could make debugging much harder and it could degrade code
readability in many ways. So, as a trade-off, I'd like to be able to do
something like:

using Sequel::CoreExtensions do
   records = DB[:some_table].
     where(:some_column.like '%A').
     except(:other_column < 3).
     where(:another_one.in [3, 6]).
     order(:sort_column.desc)
end

I know Sequel doesn't really support all extensions above, this is just
an example query why I think local refinements could be useful.

I much prefer the approach above instead of the DSL approach you
demonstrated.