Backport Object#instance_variable_defined? for Ruby < 1.8.6.

git-svn-id: http://svn-commit.rubyonrails.org/rails/trunk@7649 5ecf4fe2-1ee6-0310-87b1-e25e094e27de

activesupport/CHANGELOG

@@ -1,5 +1,7 @@
 *SVN*
 
+* Backport Object#instance_variable_defined? for Ruby < 1.8.6.  [Jeremy Kemper]
+
 * BufferedLogger#add doesn't modify the message argument.  #9702 [eigentone]
 
 * Added ActiveSupport::BufferedLogger as a duck-typing alternative (albeit with no formatter) to the Ruby Logger, which provides a very nice speed bump (inspired by Ezra's buffered logger) [DHH]

activesupport/lib/active_support/core_ext/object/instance_variables.rb

@@ -0,0 +1,8 @@
+class Object
+  # Available in 1.8.6 and later.
+  unless respond_to?(:instance_variable_defined?)
+    def instance_variable_defined?(variable)
+      instance_variables.include?(variable.to_s)
+    end
+  end
+end

activesupport/test/core_ext/object_and_class_ext_test.rb

@@ -177,6 +177,13 @@ class ObjectInstanceVariableTest < Test::Unit::TestCase
     @source.instance_variable_set(:@baz, 'baz')
   end
 
+  def test_instance_variable_defined
+    assert @source.instance_variable_defined?('@bar')
+    assert @source.instance_variable_defined?(:@bar)
+    assert !@source.instance_variable_defined?(:@foo)
+    assert !@source.instance_variable_defined?('@foo')
+  end
+
   def test_copy_instance_variables_from_without_explicit_excludes
     assert_equal [], @dest.instance_variables
     @dest.copy_instance_variables_from(@source)