Forum: Ruby-core Refinements and nested methods

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


=begin
@rosenfeld I think the point was that a better designed API could 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
----------------------------------------
Feature #4085: Refinements and nested methods
https://bugs.ruby-lang.org/issues/4085#change-34506

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

Not all column names can be represented as method names. Or can they?

Even if they could I don't like this approach. Look, I currently 
maintain
an application that has some parts written in Grails, others in plain 
Java
and others in Rails. I can do things even more advanced than what you
suggested in Grails thanks to some features in Groovy.

But the problem begins when you have some local variable (or method) 
name
that happens to be the same as the column.

In such cases the DSL approach doesn't really help and may yield to
unexpected results (from a user POV)
Em 07/12/2012 11:43, "trans (Thomas Sawyer)" <transfire@gmail.com> 
escreveu:

On 07.12.2012 16:23, Rodrigo Rosenfeld Rosas wrote:
> Not all column names can be represented as method names. Or can they?

Most columns should be possible, considering that even unicode method
names are valid.

For those cases where it's not possible there is __send__ in
BasicObject. Or you can manually generate the AST-Object that would
normally be spawned by method_missing. Or you could have a custom helper
method. Or you could just call method_missing directly.

And before you say that's ugly, compare the following:

a)

   Foo.query{__send__("`illegal_method_name") == bar}


b)
   using SomeDSLRefinement do
     Foo.query(:"`illegal_symbol_name" => :bar)
   end


Personally I consider the first one more elegant, concise and
expressive. Especially since you can actually write ruby code in the
block and thus do things dynamically.

> Even if they could I don't like this approach. Look, I currently
> maintain an application that has some parts written in Grails, others in
> plain Java and others in Rails. I can do things even more advanced than
> what you suggested in Grails thanks to some features in Groovy.
>
> But the problem begins when you have some local variable (or method)
> name that happens to be the same as the column.

Local methods are not a problem with an instance_eval'd block on
BasicObject. Local variables may conflict, but you have control over
them since they are by definition *local*.


> In such cases the DSL approach doesn't really help and may yield to
> unexpected results (from a user POV)

Those "problems" are far more benign than the havok sometimes caused by
monkey patching and usually result from a lack of understanding of the
employed metaprogramming methods. I.e. it's a problem that can be fixed
simply by increasing the user's knowledge through good documentation.



So really, i find this approach to making DSLs much cleaner than
patching around in core objects.

Of course monkey patching does have its place, I'm not going to deny
that. But DSLs shouldn't be the primary use-case for it. Glueing
together two libraries that don't interact nicely with each other or or
providing widely used utility methods throughout a whole gem/application
namespace would be far more important in my opinion.