Introduce class_attribute to declare inheritable class attributes. Writing an attribute on a subclass behaves just like overriding the superclass reader method. Unifies and replaces most usage of cattr_accessor, class_inheritable_attribute, superclass_delegating_attribute, and extlib_inheritable_attribute.

1 files changed, 47 insertions, 0 deletions

diff --git a/activesupport/test/core_ext/class/attribute_test.rb b/activesupport/test/core_ext/class/attribute_test.rb
new file mode 100644
index 0000000000..ef84b9f255
--- /dev/null
+++ b/activesupport/test/core_ext/class/attribute_test.rb
@@ -0,0 +1,47 @@
+require 'abstract_unit'
+require 'active_support/core_ext/class/attribute'
+
+class ClassAttributeTest < ActiveSupport::TestCase
+  class Base
+    class_attribute :setting
+  end
+
+  class Subclass < Base
+  end
+
+  def setup
+    @klass = Class.new { class_attribute :setting }
+    @sub = Class.new(@klass)
+  end
+
+  test 'defaults to nil' do
+    assert_nil @klass.setting
+    assert_nil @sub.setting
+  end
+
+  test 'inheritable' do
+    @klass.setting = 1
+    assert_equal 1, @sub.setting
+  end
+
+  test 'overridable' do
+    @sub.setting = 1
+    assert_nil @klass.setting
+
+    @klass.setting = 2
+    assert_equal 1, @sub.setting
+
+    assert_equal 1, Class.new(@sub).setting
+  end
+
+  test 'query method' do
+    assert_equal false, @klass.setting?
+    @klass.setting = 1
+    assert_equal true, @klass.setting?
+  end
+
+  test 'no instance delegates' do
+    assert_raise(NoMethodError) { @klass.new.setting }
+    assert_raise(NoMethodError) { @klass.new.setting? }
+  end
+end