Codechange: Replace out parameters with result tuples.

src/newgrf_generic.cpp

@@ -161,10 +161,9 @@ GenericResolverObject::GenericResolverObject(bool ai_callback, CallbackID callba
  * @param object  pre-populated resolver object
  * @param param1_grfv7 callback_param1 for GRFs up to version 7.
  * @param param1_grfv8 callback_param1 for GRFs from version 8 on.
- * @param[out] file Optionally returns the GRFFile which made the final decision for the callback result. May be nullptr if not required.
+ * @return answering GRFFile and callback value if successful, or CALLBACK_FAILED
- * @return callback value if successful or CALLBACK_FAILED
  */
-static uint16_t GetGenericCallbackResult(uint8_t feature, ResolverObject &object, uint32_t param1_grfv7, uint32_t param1_grfv8, const GRFFile **file)
+static std::pair<const GRFFile *, uint16_t> GetGenericCallbackResult(uint8_t feature, ResolverObject &object, uint32_t param1_grfv7, uint32_t param1_grfv8)
 {
 	assert(feature < lengthof(_gcl));
 
@@ -177,14 +176,11 @@ static uint16_t GetGenericCallbackResult(uint8_t feature, ResolverObject &object
 		uint16_t result = object.ResolveCallback();
 		if (result == CALLBACK_FAILED) continue;
 
-		/* Return NewGRF file if necessary */
+		return {it.file, result};
-		if (file != nullptr) *file = it.file;
-
-		return result;
 	}
 
 	/* No callback returned a valid result, so we've failed. */
-	return CALLBACK_FAILED;
+	return {nullptr, CALLBACK_FAILED};
 }
 
 
@@ -200,10 +196,9 @@ static uint16_t GetGenericCallbackResult(uint8_t feature, ResolverObject &object
  * @param event 'AI construction event' to pass to callback. (Variable 86)
  * @param count 'Construction number' to pass to callback. (Variable 87)
  * @param station_size 'Station size' to pass to callback. (Variable 88)
- * @param[out] file Optionally returns the GRFFile which made the final decision for the callback result. May be nullptr if not required.
+ * @return answering GRFFile and callback value if successful, or CALLBACK_FAILED
- * @return callback value if successful or CALLBACK_FAILED
  */
-uint16_t GetAiPurchaseCallbackResult(uint8_t feature, CargoType cargo_type, uint8_t default_selection, IndustryType src_industry, IndustryType dst_industry, uint8_t distance, AIConstructionEvent event, uint8_t count, uint8_t station_size, const GRFFile **file)
+std::pair<const GRFFile *, uint16_t> GetAiPurchaseCallbackResult(uint8_t feature, CargoType cargo_type, uint8_t default_selection, IndustryType src_industry, IndustryType dst_industry, uint8_t distance, AIConstructionEvent event, uint8_t count, uint8_t station_size)
 {
 	GenericResolverObject object(true, CBID_GENERIC_AI_PURCHASE_SELECTION);
 
@@ -229,8 +224,8 @@ uint16_t GetAiPurchaseCallbackResult(uint8_t feature, CargoType cargo_type, uint
 	object.generic_scope.station_size      = station_size;
 	object.generic_scope.feature           = feature;
 
-	uint16_t callback = GetGenericCallbackResult(feature, object, 0, 0, file);
+	auto callback = GetGenericCallbackResult(feature, object, 0, 0);
-	if (callback != CALLBACK_FAILED) callback = GB(callback, 0, 8);
+	if (callback.second != CALLBACK_FAILED) callback.second = GB(callback.second, 0, 8);
 	return callback;
 }
 
@@ -255,8 +250,7 @@ void AmbientSoundEffectCallback(TileIndex tile)
 	uint32_t param1_v8 = GetTileType(tile) << 24 | GetTileZ(tile) << 16 | GB(r, 16, 8) << 8 | (HasTileWaterClass(tile) ? GetWaterClass(tile) : 0) << 3 | GetTerrainType(tile);
 
 	/* Run callback. */
-	const GRFFile *grf_file;
+	auto callback = GetGenericCallbackResult(GSF_SOUNDFX, object, param1_v7, param1_v8);
-	uint16_t callback = GetGenericCallbackResult(GSF_SOUNDFX, object, param1_v7, param1_v8, &grf_file);
 
-	if (callback != CALLBACK_FAILED) PlayTileSound(grf_file, callback, tile);
+	if (callback.second != CALLBACK_FAILED) PlayTileSound(callback.first, callback.second, tile);
 }

src/newgrf_generic.h

@@ -47,7 +47,7 @@ static const IndustryType IT_AI_TOWN    = 0xFF; ///< The AI actually wants to tr
 void ResetGenericCallbacks();
 void AddGenericCallback(uint8_t feature, const GRFFile *file, const SpriteGroup *group);
 
-uint16_t GetAiPurchaseCallbackResult(uint8_t feature, CargoType cargo_type, uint8_t default_selection, IndustryType src_industry, IndustryType dst_industry, uint8_t distance, AIConstructionEvent event, uint8_t count, uint8_t station_size, const GRFFile **file);
+std::pair<const GRFFile *, uint16_t> GetAiPurchaseCallbackResult(uint8_t feature, CargoType cargo_type, uint8_t default_selection, IndustryType src_industry, IndustryType dst_industry, uint8_t distance, AIConstructionEvent event, uint8_t count, uint8_t station_size);
 void AmbientSoundEffectCallback(TileIndex tile);
 
 /** Play an ambient sound effect for an empty tile. */

src/script/api/script_rail.cpp

@@ -175,8 +175,7 @@
 	EnforcePrecondition(false, source_industry == ScriptIndustryType::INDUSTRYTYPE_UNKNOWN || source_industry == ScriptIndustryType::INDUSTRYTYPE_TOWN || ScriptIndustryType::IsValidIndustryType(source_industry));
 	EnforcePrecondition(false, goal_industry   == ScriptIndustryType::INDUSTRYTYPE_UNKNOWN || goal_industry   == ScriptIndustryType::INDUSTRYTYPE_TOWN || ScriptIndustryType::IsValidIndustryType(goal_industry));
 
-	const GRFFile *file;
+	auto res = GetAiPurchaseCallbackResult(
-	uint16_t res = GetAiPurchaseCallbackResult(
 		GSF_STATIONS,
 		cargo_type,
 		0,
@@ -185,17 +184,16 @@
 		ClampTo<uint8_t>(distance / 2),
 		AICE_STATION_GET_STATION_ID,
 		source_station ? 0 : 1,
-		std::min<SQInteger>(15u, num_platforms) << 4 | std::min<SQInteger>(15u, platform_length),
+		std::min<SQInteger>(15u, num_platforms) << 4 | std::min<SQInteger>(15u, platform_length)
-		&file
 	);
 
 	Axis axis = direction == RAILTRACK_NW_SE ? AXIS_Y : AXIS_X;
 	bool adjacent = station_id != ScriptStation::STATION_JOIN_ADJACENT;
 	StationID to_join = ScriptStation::IsValidStation(station_id) ? station_id : StationID::Invalid();
-	if (res != CALLBACK_FAILED) {
+	if (res.second != CALLBACK_FAILED) {
-		const StationSpec *spec = StationClass::GetByGrf(file->grfid, res);
+		const StationSpec *spec = StationClass::GetByGrf(res.first->grfid, res.second);
 		if (spec == nullptr) {
-			Debug(grf, 1, "{} returned an invalid station ID for 'AI construction/purchase selection (18)' callback", file->filename);
+			Debug(grf, 1, "{} returned an invalid station ID for 'AI construction/purchase selection (18)' callback", res.first->filename);
 		} else {
 			/* We might have gotten an usable station spec. Try to build it, but if it fails we'll fall back to the original station. */
 			if (ScriptObject::Command<CMD_BUILD_RAIL_STATION>::Do(tile, (::RailType)GetCurrentRailType(), axis, num_platforms, platform_length, spec->class_index, spec->index, to_join, adjacent)) return true;