add proper singleton methods

src/my_singleton.cpp

@@ -8,17 +8,28 @@
 
 using namespace godot;
 
+MySingleton *MySingleton::singleton = nullptr;
+
 void MySingleton::_bind_methods()
 {
 	ClassDB::bind_method(D_METHOD("hello_singleton"), &MySingleton::hello_singleton);
 }
 
+MySingleton *MySingleton::get_singleton()
+{
+	return singleton;
+}
+
 MySingleton::MySingleton()
 {
+	ERR_FAIL_COND(singleton != nullptr);
+	singleton = this;
 }
 
 MySingleton::~MySingleton()
 {
+	ERR_FAIL_COND(singleton != this);
+	singleton = nullptr;
 }
 
 void MySingleton::hello_singleton()

src/my_singleton.hpp

@@ -12,10 +12,14 @@ class MySingleton : public Object
 {
 	GDCLASS(MySingleton, Object);
 
+	static MySingleton *singleton;
+
 protected:
 	static void _bind_methods();
 
 public:
+	static MySingleton *get_singleton();
+
 	MySingleton();
 	~MySingleton();
 

src/register_types.cpp

@@ -22,7 +22,7 @@ void gdextension_initialize(ModuleInitializationLevel p_level)
 		ClassDB::register_class<MySingleton>();
 
 		_my_singleton = memnew(MySingleton);
-		Engine::get_singleton()->register_singleton("MySingleton", _my_singleton);
+		Engine::get_singleton()->register_singleton("MySingleton", MySingleton::get_singleton());
 	}
 }