Method UseUnreservedID

src/engine.cpp:548–565

* Look for an unreserved EngineID matching the local id, and reserve it if found. * @param type Vehicle type * @param grf_local_id The local id in the newgrf * @param grfid The GrfID that defines the scope of grf_local_id. * If a newgrf overrides the engines of another newgrf, the "scope grfid" is the ID of the overridden newgrf. * If dynamic_engines is disabled, all

 * @return The engine ID if present and now reserved, or EngineID::Invalid() if not.
 */
EngineID EngineOverrideManager::UseUnreservedID(VehicleType type, uint16_t grf_local_id, uint32_t grfid, bool static_access)
{
	auto &map = _engine_mngr.mappings[type];
	const auto key = EngineIDMapping::Key(INVALID_GRFID, grf_local_id);
	auto it = std::ranges::lower_bound(map, key, std::less{}, EngineIDMappingKeyProjection{});
	if (it == std::end(map) || it->Key() != key) return EngineID::Invalid();

	if (!static_access && grfid != INVALID_GRFID) {
		/* Reserve the engine slot for the new grfid. */
		it->grfid = grfid;

		/* Relocate entry to its new position in the mapping list to keep it sorted. */
		auto p = std::ranges::lower_bound(map, EngineIDMapping::Key(grfid, grf_local_id), std::less{}, EngineIDMappingKeyProjection{});
		it = Slide(it, std::next(it), p).first;
	}

	return it->engine;
}

void EngineOverrideManager::SetID(VehicleType type, uint16_t grf_local_id, uint32_t grfid, uint8_t substitute_id, EngineID engine)
{