Add Class#attached_object

Implements [Feature #12084]

Returns the object for which the receiver is the singleton class, or
raises TypeError if the receiver is not a singleton class.

1 files changed, 25 insertions, 0 deletions

diff --git a/test/ruby/test_class.rb b/test/ruby/test_class.rb
index 07c34ce9d5..8d9fde144e 100644
--- a/test/ruby/test_class.rb
+++ b/test/ruby/test_class.rb
@@ -759,6 +759,31 @@ class TestClass < Test::Unit::TestCase
     end
   end
 
+  def test_attached_object
+    c = Class.new
+    sc = c.singleton_class
+    obj = c.new
+
+    assert_equal(obj, obj.singleton_class.attached_object)
+    assert_equal(c, sc.attached_object)
+
+    assert_raise_with_message(TypeError, /is not a singleton class/) do
+      c.attached_object
+    end
+
+    assert_raise_with_message(TypeError, /`NilClass' is not a singleton class/) do
+      nil.singleton_class.attached_object
+    end
+
+    assert_raise_with_message(TypeError, /`FalseClass' is not a singleton class/) do
+      false.singleton_class.attached_object
+    end
+
+    assert_raise_with_message(TypeError, /`TrueClass' is not a singleton class/) do
+      true.singleton_class.attached_object
+    end
+  end
+
   def test_subclass_gc
     c = Class.new
     10_000.times do