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, 31 insertions, 0 deletions

diff --git a/spec/ruby/core/class/attached_object_spec.rb b/spec/ruby/core/class/attached_object_spec.rb
new file mode 100644
index 0000000000..115d5fa563
--- /dev/null
+++ b/spec/ruby/core/class/attached_object_spec.rb
@@ -0,0 +1,31 @@
+require_relative '../../spec_helper'
+
+ruby_version_is '3.2' do
+  describe "Class#attached_object" do
+    it "returns the object that is attached to a singleton class" do
+      a = Class.new
+
+      a_obj = a.new
+      a_obj.singleton_class.attached_object.should == a_obj
+    end
+
+    it "returns the class object that is attached to a class's singleton class" do
+      a = Class.new
+      singleton_class = (class << a; self; end)
+
+      singleton_class.attached_object.should == a
+    end
+
+    it "raises TypeError if the class is not a singleton class" do
+      a = Class.new
+
+      -> { a.attached_object }.should raise_error(TypeError)
+    end
+
+    it "raises TypeError for special singleton classes" do
+      -> { nil.singleton_class.attached_object }.should raise_error(TypeError)
+      -> { true.singleton_class.attached_object }.should raise_error(TypeError)
+      -> { false.singleton_class.attached_object }.should raise_error(TypeError)
+    end
+  end
+end