1 files changed, 35 insertions, 0 deletions
diff --git a/activesupport/lib/active_support/memoizable.rb b/activesupport/lib/active_support/memoizable.rb
new file mode 100644
index 0000000000..d06250171a
--- /dev/null
+++ b/activesupport/lib/active_support/memoizable.rb
@@ -0,0 +1,35 @@
+module ActiveSupport
+  module Memoizable
+    def self.included(base) #:nodoc:
+      base.extend(ClassMethods)
+    end
+
+    module ClassMethods
+      def memoize(symbol)
+        original_method = "_unmemoized_#{symbol}"
+        memoized_ivar = "@_memoized_#{symbol}"
+        raise "Already memoized #{symbol}" if instance_methods.map(&:to_s).include?(original_method)
+
+        alias_method original_method, symbol
+        class_eval <<-EOS, __FILE__, __LINE__
+          def #{symbol}
+            if defined? #{memoized_ivar}
+              #{memoized_ivar}
+            else
+              #{memoized_ivar} = #{original_method}
+            end
+          end
+        EOS
+      end
+    end
+
+    def freeze
+      methods.each do |method|
+        if m = method.to_s.match(/\A_unmemoized_(.*)/)
+          send(m[1]).freeze
+        end
+      end
+      super
+    end
+  end
+end