From 9df6edc7d78ff49d471131c8095f7c1e05a6e895 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Pedro=20J=2E=20Est=C3=A9banez?= <pedrojrulez@gmail.com>
Date: Thu, 19 Nov 2020 11:46:05 +0100
Subject: [PATCH] Warn about singleton being a Reference

(cherry picked from commit e1150bd912bd6076b8a94544c0ec32f75344976e)
---
 core/engine.cpp | 10 ++++++++++
 core/engine.h   |  5 +----
 2 files changed, 11 insertions(+), 4 deletions(-)

diff --git a/core/engine.cpp b/core/engine.cpp
index 454e889255b..9f68b9ccef2 100644
--- a/core/engine.cpp
+++ b/core/engine.cpp
@@ -236,3 +236,13 @@ Engine::Engine() {
 	_frame_step = 0;
 	editor_hint = false;
 }
+
+Engine::Singleton::Singleton(const StringName &p_name, Object *p_ptr) :
+		name(p_name),
+		ptr(p_ptr) {
+#ifdef DEBUG_ENABLED
+	if (Object::cast_to<Reference>(p_ptr)) {
+		ERR_PRINT("A class intended to be used as a singleton must *not* inherit from Reference.");
+	}
+#endif
+}
diff --git a/core/engine.h b/core/engine.h
index 4bb3f73bff3..4345a53db3d 100644
--- a/core/engine.h
+++ b/core/engine.h
@@ -42,10 +42,7 @@ public:
 	struct Singleton {
 		StringName name;
 		Object *ptr;
-		Singleton(const StringName &p_name = StringName(), Object *p_ptr = NULL) :
-				name(p_name),
-				ptr(p_ptr) {
-		}
+		Singleton(const StringName &p_name = StringName(), Object *p_ptr = NULL);
 	};
 
 private: