From c71b8c2151e097f435c8f76ffa123cc71f9d12ec Mon Sep 17 00:00:00 2001
From: Mikko Rasa <tdb@tdb.fi>
Date: Sun, 4 Dec 2022 23:32:05 +0200
Subject: [PATCH] Add move constructor and assignment from Owned of derived
 type

---
 source/game/owned.h | 20 ++++++++++++++++----
 1 file changed, 16 insertions(+), 4 deletions(-)

diff --git a/source/game/owned.h b/source/game/owned.h
index 76a7552..a30f040 100644
--- a/source/game/owned.h
+++ b/source/game/owned.h
@@ -25,10 +25,23 @@ public:
 	Owned(P *parent, Args &&... args): Owned(Handle<P>::from_object(parent), std::forward<Args>(args)...) { }
 
 	Owned(Owned &&other): Handle<T>(other) { other.ptr = nullptr; }
-	Owned &operator=(Owned &&other);
+
+	template<typename U>
+		requires std::is_base_of_v<T, U>
+	Owned(Owned<U> &&other): Handle<T>(other) { other.ptr = nullptr; }
+
+	Owned &operator=(Owned &&other) { assign(std::move(other)); return *this; }
+
+	template<typename U>
+		requires std::is_base_of_v<T, U>
+	Owned &operator=(Owned<U> &&other) { assign(std::move(other)); return *this; }
+
 	~Owned() { destroy(); }
 
 private:
+	template<typename U>
+	void assign(Owned<U> &&);
+
 	template<typename O>
 	static Stage &get_stage(O &);
 
@@ -68,14 +81,13 @@ Owned<T>::Owned(Handle<P> parent, Args &&... args)
 }
 
 template<typename T>
-Owned<T> &Owned<T>::operator=(Owned &&other)
+template<typename U>
+void Owned<T>::assign(Owned<U> &&other)
 {
 	destroy();
 
 	this->ptr = other.ptr;
 	other.ptr = nullptr;
-
-	return *this;
 }
 
 template<typename T>
-- 
2.43.0