Forum: Ruby-core Refinements and nested methods

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


Aaron, I see your point but often my queries are much more complex than 
a single mention to some column. So if I have to repeat an 
unrepresentable column multiple times I'd prefer the block approach.

When I mentioned the DSL issues I did it from my previous experience 
with Grails. In Grails you can bind the params arguments as the 
controller's method's arguments. So, consider this:

class SomeController {
  def someAction(String name) {
    MyDomainClass.find { name == name} // WTF?! I want to compare the 
"name" column to the value of the "name" param
  }
}

I know this isn't possible in Ruby (the params binding feature). But 
what if you want to compare "name" column to the result of a call to the 
"name" local (or inherited) method?
----------------------------------------
Feature #4085: Refinements and nested methods
https://bugs.ruby-lang.org/issues/4085#change-34524

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 07.12.2012 21:02, rosenfeld (Rodrigo Rosenfeld Rosas) wrote:
>      MyDomainClass.find { name == name} // WTF?! I want to compare the "name" 
column to the value of the "name" param
>    }
> }
>
> I know this isn't possible in Ruby (the params binding feature). But what if you 
want to compare "name" column to the result of a call to the "name" local (or 
inherited) method?

Named parameters? Depends. If you can splat them I would simply suggest
moving the thing to a different method which won't suffer from scoping
issues. But really, that's a Groovy-issue in so far that it gives local
variable names (method argument names essentially are local vars) a
non-local significance which robs you of the freedom of renaming them as
you desire without breaking code.

But there are solutions. Remember that it's instance_eval'd:

     MyDomainClass.find { self.name == name}

Alternatively you can teach the DSL some smartness and switch between
call and instance_eval based on arity:

     MyDomainClass.find {|d| d.name == name}


There are many ways to solve this problem without polluting any external
object.

>  So if I have to repeat an unrepresentable column multiple times I'd prefer the 
block approach.

Block approach is a bad name for this, since both approaches are using
blocks ;) Anyway, this problem can be solved too:

    Foo.dsl do
      col = __send__("illegal_name")
      col.eq(coalesce(id,title)) | col.like("%bar%")
    end

In fact, squeel provides an even more elegant solution. Since column
names often are escaped with the ` character and that's a valid method
name in ruby it provides literals that way:

    MyModel.where{other_table.`literal_name` == "bar"}


You're really bringing up edge cases here for which there are multiple
solutions. There is no necessity to monkey-patch Symbol only to build
some DSLs, really.