From 68d54a837efb1aa8ed41008eee0d93118c154238 Mon Sep 17 00:00:00 2001
From: Mikko Rasa <tdb@tdb.fi>
Date: Thu, 1 Jun 2023 10:17:56 +0300
Subject: [PATCH] Add move semantics to Variant

---
 source/core/variant.h | 48 ++++++++++++++++++++++++++++++++-----------
 1 file changed, 36 insertions(+), 12 deletions(-)

diff --git a/source/core/variant.h b/source/core/variant.h
index fccf891..5cb1b93 100644
--- a/source/core/variant.h
+++ b/source/core/variant.h
@@ -26,32 +26,39 @@ public:
 		const std::type_info &(*get_type)();
 		bool (*compare)(const char *, const char *);
 		void (*clone)(char *, const char *);
+		void (*move)(char *, char *);
 		void (*destroy)(char *);
 	};
 
 private:
+	template<typename T>
+	using EnableNotVariant = typename std::enable_if<!std::is_same<typename std::remove_cv<typename std::remove_reference<T>::type>::type, Variant>::value>::type;
+
 	const Functions *funcs = nullptr;
 	alignas(void *) char storage[INTERNAL_SIZE];
 
 public:
 	Variant() = default;
-	template<typename T>
-	Variant(const T &v) { assign(v); }
+	template<typename T, typename = EnableNotVariant<T>>
+	Variant(T &&v) { assign(std::forward<T>(v)); }
 	Variant(const Variant &v) { copy_from(v); }
+	Variant(Variant &&v) { move_from(std::move(v)); }
 	~Variant() { clear(); }
 
-	template<typename T>
-	Variant &operator=(const T &v) { assign(v); return *this; }
+	template<typename T, typename = EnableNotVariant<T>>
+	Variant &operator=(T &&v) { assign(std::forward<T>(v)); return *this; }
 
 	Variant &operator=(const Variant &v) { if(&v!=this) copy_from(v); return *this; }
+	Variant &operator=(Variant &&v) { if(&v!=this) move_from(std::move(v)); return *this; }
 
 	void clear();
 
 private:
 	template<typename T>
-	void assign(const T &);
+	void assign(T &&);
 
 	void copy_from(const Variant &);
+	void move_from(Variant &&);
 
 	template<typename T>
 	T &get();
@@ -98,12 +105,12 @@ private:
 	static const std::type_info &get_type() { return typeid(T); }
 
 	template<typename T>
-	static EnableSmall<T, void> create(char *s, const T &v)
-	{ new(s) T(v); }
+	static EnableSmall<T, void> create(char *s, T &&v)
+	{ new(s) typename std::remove_reference<T>::type(std::forward<T>(v)); }
 
 	template<typename T>
-	static EnableLarge<T, void> create(char *s, const T &v)
-	{ *reinterpret_cast<T **>(s) = new T(v); }
+	static EnableLarge<T, void> create(char *s, T &&v)
+	{ using V = typename std::remove_reference<T>::type; *reinterpret_cast<V **>(s) = new V(std::forward<T>(v)); }
 
 	template<typename T>
 	static typename std::enable_if<!IsEqualityComparable<T>::value, bool>::type compare(const char *, const char *)
@@ -125,6 +132,14 @@ private:
 	static EnableLarge<T, void> clone(char *s, const char *v)
 	{ *reinterpret_cast<T **>(s) = new T(**reinterpret_cast<const T *const *>(v)); }
 
+	template<typename T>
+	static EnableSmall<T, void> move(char *s, char *v)
+	{ new(s) T(std::move(*reinterpret_cast<T *>(v))); }
+
+	template<typename T>
+	static EnableLarge<T, void> move(char *s, char *v)
+	{ T *&p = *reinterpret_cast<T **>(v); *reinterpret_cast<T **>(s) = p; p = nullptr; }
+
 	template<typename T>
 	static EnableSmall<T, void> destroy(char *s)
 	{ reinterpret_cast<T *>(s)->~T(); }
@@ -143,11 +158,11 @@ inline void Variant::clear()
 }
 
 template<typename T>
-inline void Variant::assign(const T &v)
+inline void Variant::assign(T &&v)
 {
 	clear();
-	funcs = get_functions<typename std::remove_cv<T>::type>();
-	create(storage, v);
+	funcs = get_functions<typename std::remove_cv<typename std::remove_reference<T>::type>::type>();
+	create(storage, std::forward<T>(v));
 }
 
 inline void Variant::copy_from(const Variant &v)
@@ -157,6 +172,14 @@ inline void Variant::copy_from(const Variant &v)
 		funcs->clone(storage, v.storage);
 }
 
+inline void Variant::move_from(Variant &&v)
+{
+	clear();
+	if((funcs = v.funcs))
+		funcs->move(storage, v.storage);
+	v.clear();
+}
+
 template<typename T>
 inline T &Variant::get()
 {
@@ -187,6 +210,7 @@ inline const Variant::Functions *Variant::get_functions()
 		&get_type<T>,
 		&compare<T>,
 		&clone<T>,
+		&move<T>,
 		&destroy<T>
 	};
 	return &funcs;
-- 
2.43.0