From: Trans <transfire@...>
Date: 2005-09-23T07:36:39+09:00
Subject: Inspect, looking in from the outside

Hi--

I've been hadling a lot of OpenStruct like classes the last few days.
It isn;t alwasy smooth sailing. I've been thinking about accessing
certain "metainfo" about an object from the outside rather then from
the inside to ensure certain results. A friend say it goes against the
grain of OOP and polymorphism, but I wonder if certian "metainfo"
shouldn't? What do others think?

Also have a look at my example code below.

Thanks,
T.


---

# The Inspect module provides a guaranteed means of inspecting
# an object and seeing it for what it really is. Using a
# separate module prevents the methods from being overridden
# in the class/object being inspected. For example using the
# Inspect module methods, a Proxy object will be seen as a
# Proxy object and not it's delegate.

module Inspect
  extend self

  OBJECT_INSPECTION_METHODS = [
    :send, :dup, :clone, :object_id,
    :class, :is_a?, :kind_of?,
    :respond_to?, :method, :methods,
    :instance_variable_get, :instance_variable_set,
    :instance_eval
  ]

  CLASS_INSPECTION_METHODS = [
    :instance_methods, :class_eval, :module_eval, :method_defined?
  ]

  def define_inspection_method( name, old_name=name, from=Object )
    if from.method_defined?( old_name )
      im = from.instance_method( old_name )
      define_method(name) do |slf,*args|
        im.bind(slf).call(*args)
      end
    end
  end

  define_inspection_method( :id, :object_id )
  define_inspection_method( :var_get, :instance_variable_get )
  define_inspection_method( :var_set, :instance_variable_set )

  OBJECT_INSPECTION_METHODS.each do |m|
    define_inspection_method( m )
  end

  define_inspection_method( :class_of?, :===, Class )

  CLASS_INSPECTION_METHODS.each do |m|
    define_inspection_method( m, m, Class )
  end

  def nil?(obj)   ; is_a?(obj, NilClass)   ; end
  def false?(obj) ; is_a?(obj, FalseClass) ; end
  def true?(obj)  ; is_a?(obj, TrueClass)  ; end
  def bool?(obj)  ; is_a?(obj, FalseClass) or is_a?(obj, TrueClass) ;
end

  def null?( obj )
    defined?(NullClass) and is_a?(slf,NullClass)
  end

  def nack?( obj )
    defined?(NackClass) and is_a?(slf,NackClass)
  end

  def f?( obj )
    return true if is_a?(obj,NilClass)
    return true if defined?(NullClass) and is_a?(obj,NullClass)
    return true if defined?(NackClass) and is_a?(obj,NackClass)
    false
  end

  def t?( obj )
    return false if is_a?(obj,NilClass)
    return false if defined?(NullClass) and is_a?(obj,NullClass)
    return false if defined?(NackClass) and is_a?(obj,NackClass)
    true
  end

end

class Object
  def instance
    @_instance ||= Functor.new { |op, *args| Inspect.__send__(op, self,
*args) }
  end
end