4 files changed, 90 insertions, 0 deletions
diff --git a/activesupport/CHANGELOG b/activesupport/CHANGELOG
index 13fb1521f2..cc79c9d7c4 100644
--- a/activesupport/CHANGELOG
+++ b/activesupport/CHANGELOG
@@ -1,5 +1,11 @@
 *SVN*
 
+* attr_internal to support namespacing and deprecation. Like attr_* except backed by internally-named instance variable. Set attr_internal_naming_format to change the format from the default '@_%s'. [Jeremy Kemper]
+    # def foo()   @foo__rofl      end
+    # def foo=(v) @foo__rofl = v  end
+    self.attr_internal_naming_format = '@%s__rofl'
+    attr_internal :foo
+
 * Raise fully qualified names upon name errors. #5533 [lars@pinds.com, Nicholas Seckar]
 
 * Add extention to obtain the missing constant from NameError instances. [Nicholas Seckar]
diff --git a/activesupport/lib/active_support/core_ext/module.rb b/activesupport/lib/active_support/core_ext/module.rb
index 45069f52af..8d48de53dd 100644
--- a/activesupport/lib/active_support/core_ext/module.rb
+++ b/activesupport/lib/active_support/core_ext/module.rb
@@ -1,5 +1,6 @@
 require File.dirname(__FILE__) + '/module/inclusion'
 require File.dirname(__FILE__) + '/module/attribute_accessors'
+require File.dirname(__FILE__) + '/module/attr_internal'
 require File.dirname(__FILE__) + '/module/delegation'
 require File.dirname(__FILE__) + '/module/introspection'
 require File.dirname(__FILE__) + '/module/loading'
diff --git a/activesupport/lib/active_support/core_ext/module/attr_internal.rb b/activesupport/lib/active_support/core_ext/module/attr_internal.rb
new file mode 100644
index 0000000000..c793da7159
--- /dev/null
+++ b/activesupport/lib/active_support/core_ext/module/attr_internal.rb
@@ -0,0 +1,31 @@
+class Module
+  # Declare an attribute reader backed by an internally-named instance variable.
+  def attr_internal_reader(*attrs)
+    attrs.each do |attr|
+      module_eval "def #{attr}() #{attr_internal_ivar_name(attr)} end"
+    end
+  end
+
+  # Declare an attribute writer backed by an internally-named instance variable.
+  def attr_internal_writer(*attrs)
+    attrs.each do |attr|
+      module_eval "def #{attr}=(v) #{attr_internal_ivar_name(attr)} = v end"
+    end
+  end
+
+  # Declare attributes backed by 'internal' instance variables names.
+  def attr_internal_accessor(*attrs)
+    attr_internal_reader *attrs
+    attr_internal_writer *attrs
+  end
+
+  alias_method :attr_internal, :attr_internal_accessor
+
+  private
+    mattr_accessor :attr_internal_naming_format
+    self.attr_internal_naming_format = '@_%s'
+
+    def attr_internal_ivar_name(attr)
+      attr_internal_naming_format % attr
+    end
+end
diff --git a/activesupport/test/core_ext/module/attr_internal_test.rb b/activesupport/test/core_ext/module/attr_internal_test.rb
new file mode 100644
index 0000000000..25b049f619
--- /dev/null
+++ b/activesupport/test/core_ext/module/attr_internal_test.rb
@@ -0,0 +1,52 @@
+require File.dirname(__FILE__) + '/../../abstract_unit'
+
+class AttrInternalTest < Test::Unit::TestCase
+  def setup
+    @target = Class.new
+    @instance = @target.new
+  end
+
+  def test_attr_internal_reader
+    assert_nothing_raised { @target.attr_internal_reader :foo }
+
+    assert !@instance.instance_variables.include?('@_foo')
+    assert_raise(NoMethodError) { @instance.foo = 1 }
+
+    @instance.instance_variable_set('@_foo', 1)
+    assert_nothing_raised { assert_equal 1, @instance.foo }
+  end
+
+  def test_attr_internal_writer
+    assert_nothing_raised { @target.attr_internal_writer :foo }
+
+    assert !@instance.instance_variables.include?('@_foo')
+    assert_nothing_raised { assert_equal 1, @instance.foo = 1 }
+
+    assert_equal 1, @instance.instance_variable_get('@_foo')
+    assert_raise(NoMethodError) { @instance.foo }
+  end
+
+  def test_attr_internal_accessor
+    assert_nothing_raised { @target.attr_internal :foo }
+
+    assert !@instance.instance_variables.include?('@_foo')
+    assert_nothing_raised { assert_equal 1, @instance.foo = 1 }
+
+    assert_equal 1, @instance.instance_variable_get('@_foo')
+    assert_nothing_raised { assert_equal 1, @instance.foo }
+  end
+
+  def test_attr_internal_naming_format
+    assert_equal '@_%s', @target.attr_internal_naming_format
+    assert_nothing_raised { @target.attr_internal_naming_format = '@abc%sdef' }
+    @target.attr_internal :foo
+
+    assert !@instance.instance_variables.include?('@_foo')
+    assert !@instance.instance_variables.include?('@abcfoodef')
+    assert_nothing_raised { @instance.foo = 1 }
+    assert !@instance.instance_variables.include?('@_foo')
+    assert @instance.instance_variables.include?('@abcfoodef')
+  ensure
+    @target.attr_internal_naming_format = '@_%s'
+  end
+end