Add option to Class#class_attribute for skipping the query method

3 files changed, 18 insertions, 5 deletions

diff --git a/activesupport/CHANGELOG.md b/activesupport/CHANGELOG.md
index 3e2967f57d..fcb6b09e77 100644
--- a/activesupport/CHANGELOG.md
+++ b/activesupport/CHANGELOG.md
@@ -1,5 +1,11 @@
 ## Rails 4.0.0 (unreleased) ##
 
+*   `Class#class_attribute` accepts an `instance_predicate` option which
+    defaults to `true`. If set to `false` the predicate method will not
+    be defined.
+
+    *Agis Anastasopoulos*
+
 *   `fast_xs` support has been removed.  Use 'String#encode(xml: :attr)`.
 
 *   `ActiveSupport::Notifications::Instrumenter#instrument` should yield
diff --git a/activesupport/lib/active_support/core_ext/class/attribute.rb b/activesupport/lib/active_support/core_ext/class/attribute.rb
index e51ab9ddbc..6d49b7b6e1 100644
--- a/activesupport/lib/active_support/core_ext/class/attribute.rb
+++ b/activesupport/lib/active_support/core_ext/class/attribute.rb
@@ -44,7 +44,8 @@ class Class
   #   Base.setting               # => []
   #   Subclass.setting           # => [:foo]
   #
-  # For convenience, a query method is defined as well:
+  # For convenience, an instance predicate method is defined as well.
+  # To skip it, pass <tt>instance_predicate: false</tt>.
   #
   #   Subclass.setting?       # => false
   #
@@ -72,10 +73,11 @@ class Class
     # double assignment is used to avoid "assigned but unused variable" warning
     instance_reader = instance_reader = options.fetch(:instance_accessor, true) && options.fetch(:instance_reader, true)
     instance_writer = options.fetch(:instance_accessor, true) && options.fetch(:instance_writer, true)
+    instance_predicate = options.fetch(:instance_predicate, true)
 
     attrs.each do |name|
       define_singleton_method(name) { nil }
-      define_singleton_method("#{name}?") { !!public_send(name) }
+      define_singleton_method("#{name}?") { !!public_send(name) } if instance_predicate
 
       ivar = "@#{name}"
 
@@ -109,7 +111,7 @@ class Class
             self.class.public_send name
           end
         end
-        define_method("#{name}?") { !!public_send(name) }
+        define_method("#{name}?") { !!public_send(name) } if instance_predicate
       end
 
       attr_writer name if instance_writer
diff --git a/activesupport/test/core_ext/class/attribute_test.rb b/activesupport/test/core_ext/class/attribute_test.rb
index 1c3ba8a7a0..e7a1334db3 100644
--- a/activesupport/test/core_ext/class/attribute_test.rb
+++ b/activesupport/test/core_ext/class/attribute_test.rb
@@ -27,7 +27,7 @@ class ClassAttributeTest < ActiveSupport::TestCase
     assert_equal 1, Class.new(@sub).setting
   end
 
-  test 'query method' do
+  test 'predicate method' do
     assert_equal false, @klass.setting?
     @klass.setting = 1
     assert_equal true, @klass.setting?
@@ -48,7 +48,7 @@ class ClassAttributeTest < ActiveSupport::TestCase
     assert_equal 1, object.setting
   end
 
-  test 'instance query' do
+  test 'instance predicate' do
     object = @klass.new
     assert_equal false, object.setting?
     object.setting = 1
@@ -73,6 +73,11 @@ class ClassAttributeTest < ActiveSupport::TestCase
     assert_raise(NoMethodError) { object.setting = 'boom' }
   end
 
+  test 'disabling instance predicate' do
+    object = Class.new { class_attribute :setting, instance_predicate: false }.new
+    assert_raise(NoMethodError) { object.setting? }
+  end
+
   test 'works well with singleton classes' do
     object = @klass.new
     object.singleton_class.setting = 'foo'