1 files changed, 58 insertions, 0 deletions

diff --git a/src/FunctionRef.h b/src/FunctionRef.h
new file mode 100644
index 000000000..8215fd0db
--- /dev/null
+++ b/src/FunctionRef.h
@@ -0,0 +1,58 @@
+
+#pragma once
+
+// Declared only so it can be partially specialized
+template <class Signature>
+class cFunctionRef;
+
+/** A light-weight, type-erased reference to a function object.
+This is similar to a std::function but doesn't copy the function object
+which means that mutable function objects will be modified for the caller
+but would not be if using a std::function (See #3990 for implications of this).
+A cFunctionRef has no empty state but is non-owning and so is safe to call
+as long as the referred object is still alive. */
+template <class Ret, class... Args>
+class cFunctionRef<Ret(Args...)>
+{
+public:
+	/** Construct from a function object. */
+	template <class FunctionObject>
+	cFunctionRef(FunctionObject && a_FunctionObject)
+	{
+		// Store an opaque reference to the object.
+		m_CallableData = &a_FunctionObject;
+
+		// Along with a function that knows how to call the object.
+		m_CallFunction = &ObjectFunctionCaller<FunctionObject>;
+	}
+
+	/** Call the referenced function object */
+	Ret operator () (Args... a_Args)
+	{
+		return m_CallFunction(m_CallableData, std::forward<Args>(a_Args)...);
+	}
+
+private:
+
+	/** Function that performs the call. */
+	template <class ObjectType>
+	static Ret ObjectFunctionCaller(void * a_Callable, Args...  a_Args)
+	{
+		// Convert opaque reference to the concrete type.
+		using ObjectPtr = typename std::add_pointer<ObjectType>::type;
+		auto & Object = *static_cast<ObjectPtr>(a_Callable);
+
+		// Forward the call down to the object.
+		return Object(std::forward<Args>(a_Args)...);
+	}
+
+	using cCallFunction = Ret(*)(void *, Args...);
+
+	/** Type erased reference to a callable. */
+	void * m_CallableData;
+
+	/** Function that knows how to call the type erased reference. */
+	cCallFunction m_CallFunction;
+};
+
+