1  #!/usr/bin/env ruby
   2  #--
   3  # Copyright 2004, 2006 by Jim Weirich (jim@weirichhouse.org).
   4  # All rights reserved.
   5 
   6  # Permission is granted for use, copying, modification, distribution,
   7  # and distribution of modified versions of this work as long as the
   8  # above copyright notice is included.
   9  #++
  10 
  11  ######################################################################
  12  # BlankSlate provides an abstract base class with no predefined
  13  # methods (except for <tt>\_\_send__</tt> and <tt>\_\_id__</tt>).
  14  # BlankSlate is useful as a base class when writing classes that
  15  # depend upon <tt>method_missing</tt> (e.g. dynamic proxies).
  16  #
  17  class BlankSlate
  18    class << self
  19 
  20      # Hide the method named +name+ in the BlankSlate class.  Don't
  21      # hide +instance_eval+ or any method beginning with "__".
  22      def hide(name)
  23        if instance_methods.include?(name.to_s) and
  24          name !~ /^(__|instance_eval)/
  25          @hidden_methods ||= {}
  26          @hidden_methods[name.to_sym] = instance_method(name)
  27          undef_method name
  28        end
  29      end
  30 
  31      def find_hidden_method(name)
  32        @hidden_methods ||= {}
  33        @hidden_methods[name] || superclass.find_hidden_method(name)
  34      end
  35 
  36      # Redefine a previously hidden method so that it may be called on a blank
  37      # slate object.
  38      def reveal(name)
  39        bound_method = nil
  40        unbound_method = find_hidden_method(name)
  41        fail "Don't know how to reveal method '#{name}'" unless unbound_method
  42        define_method(name) do |*args|
  43          bound_method ||= unbound_method.bind(self)
  44          bound_method.call(*args)
  45        end
  46      end
  47    end
  48 
  49    instance_methods.each { |m| hide(m) }
  50  end
  51 
  52  ######################################################################
  53  # Since Ruby is very dynamic, methods added to the ancestors of
  54  # BlankSlate <em>after BlankSlate is defined</em> will show up in the
  55  # list of available BlankSlate methods.  We handle this by defining a
  56  # hook in the Object and Kernel classes that will hide any method
  57  # defined after BlankSlate has been loaded.
  58  #
  59  module Kernel
  60    class << self
  61      alias_method :blank_slate_method_added, :method_added
  62 
  63      # Detect method additions to Kernel and remove them in the
  64      # BlankSlate class.
  65      def method_added(name)
  66        result = blank_slate_method_added(name)
  67        return result if self != Kernel
  68        BlankSlate.hide(name)
  69        result
  70      end
  71    end
  72  end
  73 
  74  ######################################################################
  75  # Same as above, except in Object.
  76  #
  77  class Object
  78    class << self
  79      alias_method :blank_slate_method_added, :method_added
  80 
  81      # Detect method additions to Object and remove them in the
  82      # BlankSlate class.
  83      def method_added(name)
  84        result = blank_slate_method_added(name)
  85        return result if self != Object
  86        BlankSlate.hide(name)
  87        result
  88      end
  89 
  90      def find_hidden_method(name)
  91        nil
  92      end
  93    end
  94  end
  95 
  96  ######################################################################
  97  # Also, modules included into Object need to be scanned and have their
  98  # instance methods removed from blank slate.  In theory, modules
  99  # included into Kernel would have to be removed as well, but a
 100  # "feature" of Ruby prevents late includes into modules from being
 101  # exposed in the first place.
 102  #
 103  class Module
 104    alias blankslate_original_append_features append_features
 105    def append_features(mod)
 106      result = blankslate_original_append_features(mod)
 107      return result if mod != Object
 108      instance_methods.each do |name|
 109        BlankSlate.hide(name)
 110      end
 111      result
 112    end
 113  en