2 files changed, 33 insertions, 0 deletions
diff --git a/activesupport/lib/active_support.rb b/activesupport/lib/active_support.rb
index 1a8603e892..0526057b15 100644
--- a/activesupport/lib/active_support.rb
+++ b/activesupport/lib/active_support.rb
@@ -43,6 +43,7 @@ require 'active_support/ordered_hash'
 require 'active_support/ordered_options'
 require 'active_support/option_merger'
 
+require 'active_support/memoizable'
 require 'active_support/string_inquirer'
 
 require 'active_support/values/time_zone'
diff --git a/activesupport/lib/active_support/memoizable.rb b/activesupport/lib/active_support/memoizable.rb
new file mode 100644
index 0000000000..c78fb0a793
--- /dev/null
+++ b/activesupport/lib/active_support/memoizable.rb
@@ -0,0 +1,32 @@
+module ActiveSupport
+  module Memoizable
+    def self.included(base) #:nodoc:
+      base.extend(ClassMethods)
+    end
+
+    module ClassMethods
+      def memorize(symbol)
+        original_method = "_unmemorized_#{symbol}"
+        alias_method original_method, symbol
+        class_eval <<-EOS, __FILE__, __LINE__
+          def #{symbol}
+            if instance_variable_defined?(:@#{symbol})
+              @#{symbol}
+            else
+              @#{symbol} = #{original_method}
+            end
+          end
+        EOS
+      end
+    end
+
+    def freeze
+      methods.each do |method|
+        if m = method.to_s.match(/^_unmemorized_(.*)/)
+          send(m[1]).freeze
+        end
+      end
+      super
+    end
+  end
+end