From 990d41f9f7f79443d1b2fff2c993fc342b1c5982 Mon Sep 17 00:00:00 2001
From: "Yukihiro \"Matz\" Matsumoto" <matz@ruby.or.jp>
Date: Fri, 9 Dec 2022 17:30:17 +0900
Subject: [PATCH] mruby-class-ext: new method `attached_object` introduced in
 Ruby3.2

---
 mrbgems/mruby-class-ext/src/class.c   | 30 +++++++++++++++++++++++++++
 mrbgems/mruby-class-ext/test/class.rb | 16 ++++++++++++++
 2 files changed, 46 insertions(+)

diff --git a/mrbgems/mruby-class-ext/src/class.c b/mrbgems/mruby-class-ext/src/class.c
index 141264bb6..dbe061524 100644
--- a/mrbgems/mruby-class-ext/src/class.c
+++ b/mrbgems/mruby-class-ext/src/class.c
@@ -3,6 +3,8 @@
 #include "mruby/string.h"
 #include "mruby/array.h"
 #include "mruby/proc.h"
+#include "mruby/variable.h"
+#include "mruby/presym.h"
 
 static mrb_value
 mrb_mod_name(mrb_state *mrb, mrb_value self)
@@ -108,6 +110,33 @@ mrb_class_subclasses(mrb_state *mrb, mrb_value self)
   return ary;
 }
 
+/*
+ *  call-seq:
+ *     attached_object -> object
+ *
+ *  Returns the object for which the receiver is the singleton class.
+ *  Raises an TypeError if the class is not a singleton class.
+ *
+ *     class Foo; end
+ *
+ *     Foo.singleton_class.attached_object        #=> Foo
+ *     Foo.attached_object                        #=> TypeError: not a singleton class
+ *     Foo.new.singleton_class.attached_object    #=> #<Foo:0x000000010491a370>
+ *     TrueClass.attached_object                  #=> TypeError: not a singleton class
+ *     NilClass.attached_object                   #=> TypeError: not a singleton class
+ */
+static mrb_value
+mrb_class_attached_object(mrb_state *mrb, mrb_value self)
+{
+  struct RClass *c;
+
+  c = mrb_class_ptr(self);
+  if (c->tt != MRB_TT_SCLASS) {
+    mrb_raise(mrb, E_TYPE_ERROR, "not a singleton class");
+  }
+  return mrb_obj_iv_get(mrb, (struct RObject*)c, MRB_SYM(__attached__));
+}
+
 void
 mrb_mruby_class_ext_gem_init(mrb_state *mrb)
 {
@@ -120,6 +149,7 @@ mrb_mruby_class_ext_gem_init(mrb_state *mrb)
 
   struct RClass *cls = mrb->class_class;
   mrb_define_method(mrb, cls, "subclasses", mrb_class_subclasses, MRB_ARGS_NONE());
+  mrb_define_method(mrb, cls, "attached_object", mrb_class_attached_object, MRB_ARGS_NONE());
 }
 
 void
diff --git a/mrbgems/mruby-class-ext/test/class.rb b/mrbgems/mruby-class-ext/test/class.rb
index 2043b39cb..fba2a19f9 100644
--- a/mrbgems/mruby-class-ext/test/class.rb
+++ b/mrbgems/mruby-class-ext/test/class.rb
@@ -11,3 +11,19 @@ assert 'Class#subclasses' do
   assert_equal([c], b.subclasses)
   assert_equal([], c.subclasses)
 end
+
+assert 'Class#attached_object' do
+  foo = Class.new
+  foo_s = class <<foo
+    foo_s = self
+  end
+  assert_equal(foo, foo_s.attached_object)
+  fooi = foo.new
+  fooi_s = class <<fooi
+    fooi_s = self
+  end
+  assert_equal(fooi, fooi_s.attached_object)
+  assert_raise(TypeError){foo.attached_object}
+  assert_raise(TypeError){TrueClass.attached_object}
+  assert_raise(TypeError){NilClass.attached_object}
+end