implemented Module#singleton_class?

mrbgems/mruby-class-ext/src/class.c

@@ -9,12 +9,19 @@ mrb_mod_name(mrb_state *mrb, mrb_value self)
   return mrb_nil_p(name)? name : mrb_str_dup(mrb, name);
 }
 
+static mrb_value
+mrb_mod_singleton_class_p(mrb_state *mrb, mrb_value self)
+{
+  return mrb_bool_value(mrb_type(self) == MRB_TT_SCLASS);
+}
+
 void
 mrb_mruby_class_ext_gem_init(mrb_state *mrb)
 {
   struct RClass *mod = mrb->module_class;
 
   mrb_define_method(mrb, mod, "name", mrb_mod_name, MRB_ARGS_NONE());
+  mrb_define_method(mrb, mod, "singleton_class?", mrb_mod_singleton_class_p, MRB_ARGS_NONE());
 }
 
 void

mrbgems/mruby-class-ext/test/module.rb

@@ -8,3 +8,13 @@ assert 'Module#name' do
   assert_equal 'Fixnum', Fixnum.name
   assert_equal 'A::B', A::B.name
 end
+
+assert 'Module#singleton_class?' do
+  mod = Module.new
+  cls = Class.new
+  scl = cls.singleton_class
+
+  assert_false mod.singleton_class?
+  assert_false cls.singleton_class?
+  assert_true scl.singleton_class?
+end