Object#instance_exec produces fewer garbage methods.

git-svn-id: http://svn-commit.rubyonrails.org/rails/trunk@7621 5ecf4fe2-1ee6-0310-87b1-e25e094e27de

activesupport/CHANGELOG

@@ -1,5 +1,7 @@
 *SVN*
 
+* Object#instance_exec produces fewer garbage methods.  [Mauricio Fernandez]
+
 * Decode json strings as Dates/Times if they're using a YAML-compatible format.  Closes #9614 [Rick]
 
 * Fixed cache_page to use the request url instead of the routing options when picking a save path #8614 [josh]

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

@@ -44,8 +44,29 @@ class Object
   end
 
   unless defined? instance_exec # 1.9
-    def instance_exec(*arguments, &block) #:nodoc:
-      block.bind(self)[*arguments]
+    module InstanceExecMethods #:nodoc:
+    end
+    include InstanceExecMethods
+
+    # Evaluate the block with the given arguments within the context of
+    # this object, so self is set to the method receiver.
+    #
+    # From Mauricio's http://eigenclass.org/hiki/bounded+space+instance_exec
+    def instance_exec(*args, &block)
+      begin
+        old_critical, Thread.critical = Thread.critical, true
+        n = 0
+        n += 1 while respond_to?(method_name = "__instance_exec#{n}")
+        InstanceExecMethods.module_eval { define_method(method_name, &block) }
+      ensure
+        Thread.critical = old_critical
+      end
+
+      begin
+        send(method_name, *args)
+      ensure
+        InstanceExecMethods.module_eval { remove_method(method_name) } rescue nil
+      end
     end
   end
 end

activesupport/test/core_ext/object_and_class_ext_test.rb

@@ -216,8 +216,15 @@ class ObjectInstanceVariableTest < Test::Unit::TestCase
   end
 
   def test_instance_exec_passes_arguments_to_block
-    block = Proc.new { |value| [self, value] }
-    assert_equal %w(hello goodbye), 'hello'.instance_exec('goodbye', &block)
+    assert_equal %w(hello goodbye), 'hello'.instance_exec('goodbye') { |v| [self, v] }
   end
 
+  def test_instance_exec_with_frozen_obj
+    assert_equal %w(olleh goodbye), 'hello'.freeze.instance_exec('goodbye') { |v| [reverse, v] }
+  end
+
+  def test_instance_exec_nested
+    assert_equal %w(goodbye olleh bar), 'hello'.instance_exec('goodbye') { |arg|
+      [arg] + instance_exec('bar') { |v| [reverse, v] } }
+  end
 end