vendor/rails/activesupport/lib/active_support/vendor/builder-2.1.2/blankslate.rb

   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 end