Merge pull request #1541 from mc-server/VariadicTemplates

cLuaState::Call() uses variadic templates

src/Bindings/LuaState.h

@@ -240,10 +240,24 @@ public:
 	/** Retrieve value at a_StackPos, if it is a valid cWorld class. If not, a_Value is unchanged */
 	void GetStackValue(int a_StackPos, pWorld & a_Value);
 	
+	/** Call the specified Lua function.
+	Returns true if call succeeded, false if there was an error.
+	A special param of cRet & signifies the end of param list and the start of return values.
+	Example call: Call(Fn, Param1, Param2, Param3, cLuaState::Return, Ret1, Ret2) */
+	template <typename FnT, typename... Args>
+	bool Call(const FnT & a_Function, Args &&... args)
+	{
+		PushFunction(a_Function);
+		return PushCallPop(args...);
+	}
 
-	// Include the cLuaState::Call() overload implementation that is generated by the gen_LuaState_Call.lua script:
-	#include "LuaState_Call.inc"
-
+	/** Retrieves a list of values from the Lua stack, starting at the specified index. */
+	template <typename T, typename... Args>
+	inline void GetStackValues(int a_StartStackPos, T & a_Ret, Args &&... args)
+	{
+		GetStackValue(a_StartStackPos, a_Ret);
+		GetStackValues(a_StartStackPos + 1, args...);
+	}
 
 	/** Returns true if the specified parameters on the stack are of the specified usertable type; also logs warning if not. Used for static functions */
 	bool CheckParamUserTable(int a_StartParam, const char * a_UserTable, int a_EndParam = -1);
@@ -310,6 +324,7 @@ public:
 	static void LogStack(lua_State * a_LuaState, const char * a_Header = NULL);
 	
 protected:
+
 	lua_State * m_LuaState;
 	
 	/** If true, the state is owned by this object and will be auto-Closed. False => attached state */
@@ -327,6 +342,63 @@ protected:
 	int m_NumCurrentFunctionArgs;
 
 
+	/** Variadic template terminator: Counting zero args returns zero. */
+	int CountArgs(void)
+	{
+		return 0;
+	}
+
+	/** Variadic template: Counting args means add one to the count of the rest. */
+	template <typename T, typename... Args>
+	int CountArgs(T, Args... args)
+	{
+		return 1 + CountArgs(args...);
+	}
+
+	/** Variadic template terminator: If there's nothing more to push / pop, just call the function.
+	Note that there are no return values either, because those are prefixed by a cRet value, so the arg list is never empty. */
+	bool PushCallPop(void)
+	{
+		return CallFunction(0);
+	}
+
+	/** Variadic template recursor: More params to push. Push them and recurse. */
+	template<typename T, typename... Args>
+	inline bool PushCallPop(T a_Param, Args &&... args)
+	{
+		Push(a_Param);
+		return PushCallPop(args...);
+	}
+
+	/** Variadic template terminator: If there's nothing more to push, but return values to collect, call the function and collect the returns. */
+	template <typename... Args>
+	bool PushCallPop(cLuaState::cRet, Args &&... args)
+	{
+		// Calculate the number of return values (number of args left):
+		int NumReturns = CountArgs(args...);
+
+		// Call the function:
+		if (!CallFunction(NumReturns))
+		{
+			return false;
+		}
+
+		// Collect the return values:
+		GetStackValues(-NumReturns, args...);
+		lua_pop(m_LuaState, NumReturns);
+
+		// All successful:
+		return true;
+	}
+
+	/** Variadic template terminator: If there are no more values to get, bail out.
+	This function is not available in the public API, because it's an error to request no values directly; only internal functions can do that.
+	If you get a compile error saying this function is not accessible, check your calling code, you aren't reading any stack values. */
+	void GetStackValues(int a_StartingStackPos)
+	{
+		// Do nothing
+	}
+
 	/** Pushes the function of the specified name onto the stack.
 	Returns true if successful. Logs a warning on failure (incl. m_SubsystemName)
 	*/