libcamera: bound_method: Support bindings to non-void methods

The bound method implementation is restricted to binding to void methods
as return values are not supported. This complicates usage of bound
methods, as non-void methods used a slots or Object::invokeMethod()
targets need to be wrapped in a void method. Simplify this by supporting
arbitrary return types and ignoring the return value.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Niklas Söderlund <niklas.soderlund@ragnatech.se>

4 files changed, 41 insertions, 38 deletions

diff --git a/include/libcamera/bound_method.h b/include/libcamera/bound_method.h
index d194cd41..b50072ff 100644
--- a/include/libcamera/bound_method.h
+++ b/include/libcamera/bound_method.h
@@ -79,7 +79,7 @@ public:
 	std::tuple<typename std::remove_reference<Args>::type...> args_;
 };
 
-template<typename... Args>
+template<typename R, typename... Args>
 class BoundMethodArgs : public BoundMethodBase
 {
 public:
@@ -107,19 +107,19 @@ public:
 	virtual void invoke(Args... args) = 0;
 };
 
-template<typename T, typename... Args>
-class BoundMemberMethod : public BoundMethodArgs<Args...>
+template<typename T, typename R, typename... Args>
+class BoundMemberMethod : public BoundMethodArgs<R, Args...>
 {
 public:
-	using PackType = typename BoundMethodArgs<Args...>::PackType;
+	using PackType = typename BoundMethodArgs<R, Args...>::PackType;
 
-	BoundMemberMethod(T *obj, Object *object, void (T::*func)(Args...),
+	BoundMemberMethod(T *obj, Object *object, R (T::*func)(Args...),
 			  ConnectionType type = ConnectionTypeAuto)
-		: BoundMethodArgs<Args...>(obj, object, type), func_(func)
+		: BoundMethodArgs<R, Args...>(obj, object, type), func_(func)
 	{
 	}
 
-	bool match(void (T::*func)(Args...)) const { return func == func_; }
+	bool match(R (T::*func)(Args...)) const { return func == func_; }
 
 	void activate(Args... args, bool deleteMethod = false) override
 	{
@@ -135,20 +135,20 @@ public:
 	}
 
 private:
-	void (T::*func_)(Args...);
+	R (T::*func_)(Args...);
 };
 
-template<typename... Args>
-class BoundStaticMethod : public BoundMethodArgs<Args...>
+template<typename R, typename... Args>
+class BoundStaticMethod : public BoundMethodArgs<R, Args...>
 {
 public:
-	BoundStaticMethod(void (*func)(Args...))
-		: BoundMethodArgs<Args...>(nullptr, nullptr, ConnectionTypeAuto),
+	BoundStaticMethod(R (*func)(Args...))
+		: BoundMethodArgs<R, Args...>(nullptr, nullptr, ConnectionTypeAuto),
 		  func_(func)
 	{
 	}
 
-	bool match(void (*func)(Args...)) const { return func == func_; }
+	bool match(R (*func)(Args...)) const { return func == func_; }
 
 	void activate(Args... args, bool deleteMethod = false) override
 	{
@@ -158,7 +158,7 @@ public:
 	void invoke(Args...) override {}
 
 private:
-	void (*func_)(Args...);
+	R (*func_)(Args...);
 };
 
 } /* namespace libcamera */
diff --git a/include/libcamera/object.h b/include/libcamera/object.h
index c45165de..586c2cf6 100644
--- a/include/libcamera/object.h
+++ b/include/libcamera/object.h
@@ -29,13 +29,13 @@ public:
 
 	void postMessage(std::unique_ptr<Message> msg);
 
-	template<typename T, typename... FuncArgs, typename... Args,
+	template<typename T, typename R, typename... FuncArgs, typename... Args,
 		 typename std::enable_if<std::is_base_of<Object, T>::value>::type * = nullptr>
-	void invokeMethod(void (T::*func)(FuncArgs...), ConnectionType type,
+	void invokeMethod(R (T::*func)(FuncArgs...), ConnectionType type,
 			  Args... args)
 	{
 		T *obj = static_cast<T *>(this);
-		auto *method = new BoundMemberMethod<T, FuncArgs...>(obj, this, func, type);
+		auto *method = new BoundMemberMethod<T, R, FuncArgs...>(obj, this, func, type);
 		method->activate(args..., true);
 	}
 
diff --git a/include/libcamera/signal.h b/include/libcamera/signal.h
index 57598335..7fbe5a2c 100644
--- a/include/libcamera/signal.h
+++ b/include/libcamera/signal.h
@@ -54,27 +54,28 @@ public:
 	}
 
 #ifndef __DOXYGEN__
-	template<typename T, typename std::enable_if<std::is_base_of<Object, T>::value>::type * = nullptr>
-	void connect(T *obj, void (T::*func)(Args...),
+	template<typename T, typename R, typename std::enable_if<std::is_base_of<Object, T>::value>::type * = nullptr>
+	void connect(T *obj, R (T::*func)(Args...),
 		     ConnectionType type = ConnectionTypeAuto)
 	{
 		Object *object = static_cast<Object *>(obj);
 		object->connect(this);
-		slots_.push_back(new BoundMemberMethod<T, Args...>(obj, object, func, type));
+		slots_.push_back(new BoundMemberMethod<T, void, Args...>(obj, object, func, type));
 	}
 
-	template<typename T, typename std::enable_if<!std::is_base_of<Object, T>::value>::type * = nullptr>
+	template<typename T, typename R, typename std::enable_if<!std::is_base_of<Object, T>::value>::type * = nullptr>
 #else
-	template<typename T>
+	template<typename T, typename R>
 #endif
-	void connect(T *obj, void (T::*func)(Args...))
+	void connect(T *obj, R (T::*func)(Args...))
 	{
-		slots_.push_back(new BoundMemberMethod<T, Args...>(obj, nullptr, func));
+		slots_.push_back(new BoundMemberMethod<T, R, Args...>(obj, nullptr, func));
 	}
 
-	void connect(void (*func)(Args...))
+	template<typename R>
+	void connect(R (*func)(Args...))
 	{
-		slots_.push_back(new BoundStaticMethod<Args...>(func));
+		slots_.push_back(new BoundStaticMethod<R, Args...>(func));
 	}
 
 	void disconnect()
@@ -90,11 +91,12 @@ public:
 		SignalBase::disconnect(obj);
 	}
 
-	template<typename T>
-	void disconnect(T *obj, void (T::*func)(Args...))
+	template<typename T, typename R>
+	void disconnect(T *obj, R (T::*func)(Args...))
 	{
 		for (auto iter = slots_.begin(); iter != slots_.end(); ) {
-			BoundMethodArgs<Args...> *slot = static_cast<BoundMethodArgs<Args...> *>(*iter);
+			BoundMethodArgs<R, Args...> *slot =
+				static_cast<BoundMethodArgs<R, Args...> *>(*iter);
 			/*
 			 * If the object matches the slot, the slot is
 			 * guaranteed to be a member slot, so we can safely
@@ -102,7 +104,7 @@ public:
 			 * func.
 			 */
 			if (slot->match(obj) &&
-			    static_cast<BoundMemberMethod<T, Args...> *>(slot)->match(func)) {
+			    static_cast<BoundMemberMethod<T, R, Args...> *>(slot)->match(func)) {
 				iter = slots_.erase(iter);
 				delete slot;
 			} else {
@@ -111,12 +113,13 @@ public:
 		}
 	}
 
-	void disconnect(void (*func)(Args...))
+	template<typename R>
+	void disconnect(R (*func)(Args...))
 	{
 		for (auto iter = slots_.begin(); iter != slots_.end(); ) {
-			BoundMethodArgs<Args...> *slot = *iter;
+			BoundMethodArgs<R, Args...> *slot = *iter;
 			if (slot->match(nullptr) &&
-			    static_cast<BoundStaticMethod<Args...> *>(slot)->match(func)) {
+			    static_cast<BoundStaticMethod<R, Args...> *>(slot)->match(func)) {
 				iter = slots_.erase(iter);
 				delete slot;
 			} else {
@@ -133,7 +136,7 @@ public:
 		 */
 		std::vector<BoundMethodBase *> slots{ slots_.begin(), slots_.end() };
 		for (BoundMethodBase *slot : slots)
-			static_cast<BoundMethodArgs<Args...> *>(slot)->activate(args...);
+			static_cast<BoundMethodArgs<void, Args...> *>(slot)->activate(args...);
 	}
 };
 
diff --git a/src/libcamera/signal.cpp b/src/libcamera/signal.cpp
index 6ee348ac..19003331 100644
--- a/src/libcamera/signal.cpp
+++ b/src/libcamera/signal.cpp
@@ -54,7 +54,7 @@ namespace libcamera {
  */
 
 /**
- * \fn Signal::connect(T *object, void(T::*func)(Args...))
+ * \fn Signal::connect(T *object, R (T::*func)(Args...))
  * \brief Connect the signal to a member function slot
  * \param[in] object The slot object pointer
  * \param[in] func The slot member function
@@ -66,7 +66,7 @@ namespace libcamera {
  */
 
 /**
- * \fn Signal::connect(void(*func)(Args...))
+ * \fn Signal::connect(R (*func)(Args...))
  * \brief Connect the signal to a static function slot
  * \param[in] func The slot static function
  */
@@ -83,14 +83,14 @@ namespace libcamera {
  */
 
 /**
- * \fn Signal::disconnect(T *object, void(T::*func)(Args...))
+ * \fn Signal::disconnect(T *object, R (T::*func)(Args...))
  * \brief Disconnect the signal from the \a object slot member function \a func
  * \param[in] object The object pointer whose slots to disconnect
  * \param[in] func The slot member function to disconnect
  */
 
 /**
- * \fn Signal::disconnect(void(*func)(Args...))
+ * \fn Signal::disconnect(R (*func)(Args...))
  * \brief Disconnect the signal from the slot static function \a func
  * \param[in] func The slot static function to disconnect
  */