Added Memoizable mixin for caching simple lazy loaded attributes

activesupport/CHANGELOG

@@ -1,5 +1,7 @@
 *Edge*
 
+* Added Memoizable mixin for caching simple lazy loaded attributes [Josh Peek]
+
 * Move the test related core_ext stuff out of core_ext so it's only loaded by the test helpers.  [Michael Koziarski]
 
 * Add Inflection rules for String#humanize. #535 [dcmanges]

activesupport/lib/active_support.rb

@@ -43,6 +43,7 @@
 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'

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

activesupport/test/memoizable_test.rb

@@ -0,0 +1,45 @@
+require 'abstract_unit'
+
+uses_mocha 'Memoizable' do
+  class MemoizableTest < Test::Unit::TestCase
+    class Person
+      include ActiveSupport::Memoizable
+
+      def name
+        fetch_name_from_floppy
+      end
+      memorize :name
+
+      def age
+        nil
+      end
+      memorize :age
+
+      private
+        def fetch_name_from_floppy
+          "Josh"
+        end
+    end
+
+    def test_memoization
+      person = Person.new
+      assert_equal "Josh", person.name
+
+      person.expects(:fetch_name_from_floppy).never
+      2.times { assert_equal "Josh", person.name }
+    end
+
+    def test_memoized_methods_are_frozen
+      person = Person.new
+      person.freeze
+      assert_equal "Josh", person.name
+      assert_equal true, person.name.frozen?
+    end
+
+    def test_memoization_frozen_with_nil_value
+      person = Person.new
+      person.freeze
+      assert_equal nil, person.age
+    end
+  end
+end