Refactoring switch or if/else statement? [closed] - c++

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i'm working on a school project and got some feedback from my teacher. He said that in my code there are some bad practices, he said that the switch cases could be replaced by a polymorphic approach. Only i have no clue how i could do this.
My code is receiving messages from a CAN bus. Those messages come from different devices, I check the messages from which device they come from. If there is a new device I create a object and parse the message and store the information.
This system is pretty much the same for each message.
Here is my code.
void Application::PollWhisperConnectBus()
{
HAL_GPIO_TogglePin(PORT_LED1, PIN_LED1);
whisper_connect_id_ = hcan2.pRxMsg->StdId;
if (whisper_connect_id_ >= 0x580 && whisper_connect_id_ <= 0x58F)
{
WIBDevice();
}
if (whisper_connect_id_ >= 0x590 && whisper_connect_id_ <= 0x59F)
{
BMSSDevice();
}
if (whisper_connect_id_ >= 0x5B0 && whisper_connect_id_ <= 0x5BF)
{
DCPowerCubeDevice();
}
if (whisper_connect_id_ >= 0x5C0 && whisper_connect_id_ <= 0x5CF)
{
ACPowerCubeDevice();
}
if (whisper_connect_id_ >= 0x700 && whisper_connect_id_ <= 0x70F)
{
WIBHeartBeatDevice();
}
}
This is one of the functions which checked if there is an object of the class, if so parse the message.
void Application::DCPowerCubeDevice()
{
bool found_device = false;
int device = (hcan2.pRxMsg->StdId & 0x0F) + device_instance_offset_;
WhisperConnectDevice* whisper_connect_device;
for(unsigned int i = 0; i < whisper_connect_device_list_.size(); ++i)
{
if ((whisper_connect_device = whisper_connect_device_list_.at(i)) != NULL &&
whisper_connect_device->GetClassName() == "DCPowerCube")
{
DCPowerCube* dc_powercube = dynamic_cast<DCPowerCube*>(whisper_connect_device);
if (dc_powercube != NULL)
{
if (dc_powercube->GetDevice() == device)
{
dc_powercube->ParseCanMessage(&hcan2);
found_device = true;
break;
}
}
}
}
if (!found_device)
{
WhisperConnectDevice* dc_powercube;
if ((dc_powercube = new DCPowerCube) != NULL)
{
dc_powercube->SetDevice(device);
int n2k_address = nmea2000_.FindFirstFreeCanId(n2k_address_, device_list_);
if (n2k_address != 0xFFFF)
{
dc_powercube->SetSrcCanId(n2k_address);
dc_powercube->SetDeviceInstanceOffset(device_instance_offset_);
dc_powercube->SetDeviceInstance(0x30 + device);
dc_powercube->AddressClaim(nmea2000_);
dc_powercube->SendPGN126996(nmea2000_);
dc_powercube->SendPGN126998(nmea2000_, "DCPowerCube", "", "");
device_list_.at(n2k_address) = 0x01;
}
DCPowerCube* dc_powercube2 = dynamic_cast<DCPowerCube*>(dc_powercube);
if (dc_powercube2 != NULL)
{
dc_powercube2->SetCurrentLimit(16);
}
AddToWPCDeviceList(dc_powercube);
}
}
}
void DCPowerCube::ParseCanMessage(CAN_HandleTypeDef *can_handle)
{
if (can_handle != NULL)
{
uint16_t message_index = (can_handle->pRxMsg->Data[1] << 8) + can_handle->pRxMsg->Data[2];
switch (message_index)
{
case 0x1008:
device_name_[0] = can_handle->pRxMsg->Data[4];
device_name_[1] = can_handle->pRxMsg->Data[5];
device_name_[2] = can_handle->pRxMsg->Data[6];
device_name_[3] = can_handle->pRxMsg->Data[7];
device_name_[4] = '\0';
break;
case 0x100A:
software_version_[0] = can_handle->pRxMsg->Data[4];
software_version_[1] = can_handle->pRxMsg->Data[5];
software_version_[2] = can_handle->pRxMsg->Data[6];
software_version_[3] = can_handle->pRxMsg->Data[7];
software_version_[4] = '\0';
break;
case 0x1018:
serial_number_ = can_handle->pRxMsg->Data[4] << 24 | can_handle->pRxMsg->Data[5] << 16 |
can_handle->pRxMsg->Data[6] << 8 | can_handle->pRxMsg->Data[7];
break;
case 0x2100: // DC PowerCube status
power_cube_status_ = can_handle->pRxMsg->Data[4];
io_status_bit_ = can_handle->pRxMsg->Data[5];
dip_switch_status_bit_ = can_handle->pRxMsg->Data[6];
break;
case 0x2111: // Grid voltage, current, current limit
grid_voltage_ = (can_handle->pRxMsg->Data[4] << 8) + can_handle->pRxMsg->Data[5];
grid_current_ = can_handle->pRxMsg->Data[6];
grid_current_limit_ = can_handle->pRxMsg->Data[7];
break;
case 0x2112: // Generator frequency, RPM
generator_freq_ = (can_handle->pRxMsg->Data[4] << 8) + can_handle->pRxMsg->Data[5];
rpm_ = (can_handle->pRxMsg->Data[6] << 8) + can_handle->pRxMsg->Data[7];
break;
case 0x2113: // Generator current
gen_current_phase1_ = can_handle->pRxMsg->Data[4];
gen_current_phase2_ = can_handle->pRxMsg->Data[5];
gen_current_phase3_ = can_handle->pRxMsg->Data[6];
gen_current_limit_ = can_handle->pRxMsg->Data[7];
break;
case 0x2114: // Load percentage
grid_load_ = can_handle->pRxMsg->Data[4];
generator_load_ = can_handle->pRxMsg->Data[5];
dc_output_load_ = can_handle->pRxMsg->Data[6];
break;
case 0x2151: // Battery type & charger state
battery_type_ = can_handle->pRxMsg->Data[4];
charger_state_ = can_handle->pRxMsg->Data[5];
break;
case 0x2152: // DC output voltage & DC slave voltage
dc_output_voltage_ = (can_handle->pRxMsg->Data[4] << 8) + can_handle->pRxMsg->Data[5];
dc_slave_voltage_ = (can_handle->pRxMsg->Data[6] << 8) + can_handle->pRxMsg->Data[7];
break;
case 0x2153: // DC output current & DC output current limit
dc_output_current_ = (can_handle->pRxMsg->Data[4] << 8) + can_handle->pRxMsg->Data[5];
dc_output_current_limit_ = (can_handle->pRxMsg->Data[6] << 8) + can_handle->pRxMsg->Data[7];
break;
case 0x21A0: // Temperature sensor
temp_sens_BTS_ = can_handle->pRxMsg->Data[4];
temp_sens_intern1_ = can_handle->pRxMsg->Data[5];
temp_sens_intern2_ = can_handle->pRxMsg->Data[6];
temp_sens_intern3_ = can_handle->pRxMsg->Data[7];
break;
case 0x21A1:
break;
}
}
}
The WhisperConnectDevice is the base class of DCPowerCube.
I would love to get some feedback on how to approach this problem.

Answer 1

Whether or not you introduce polymorphism it appears you have to map an externally provided type number (ID) to code so you will always need some structure inbetween.
Your candidates are:
A block of if statements probably if-else-if...
A switch statement (if values are ameanable)
Some kind of look-up table (array, associative map, other...)
You've already got if but could improve with if-else-if.
That is normally considered the ugliest high-maintenance potential coding hot-spot approach. Coding hot-spot because all new IDs return to this code block.
I also notice in this case all your ranges are 0xnn0 to 0xnnF inclusive for some nn so you can at least simplify by reducing out the low 4 bits:
auto whisper_connect_type = whisper_connect_id_ >> 4;
Your switch option is then simplified to:
switch(whisper_connect_type) {
case 0x58: WIBDevice(); break;
case 0x59: BMSSDevice(); break;
case 0x5B: DCPowerCubeDevice(); break;
case 0x5C: ACPowerCubeDevice(); break;
case 0x70: WIBHeartBeatDevice(); break;
default: HandleUnknownDeviceIDError(whisper_connect_id_); break;
}
NB: I very strongly recommend some code to handle an unsupported ID. My advice is throwing an exception or something leading to termination. The break; is for completeness. I don't think you're coming back from an unknown ID.
An alternative is to define an associative map:
#include <iostream>
#include <unordered_map>
#include <memory>
class WhisperHandler {
public:
virtual void HandleWhisper() const = 0 ;
virtual ~WhisperHandler() {}
};
class WhisperHandlerWIBDevice : public WhisperHandler {
public:
void HandleWhisper() const override {
std::cout << "Handler WIBDevice...\n";
}
} ;
int main() {
std::unordered_map<unsigned,std::unique_ptr<const WhisperHandler>> handlers;
//...
std::unique_ptr<const WhisperHandler> handler(std::make_unique<const WhisperHandlerWIBDevice>());
std::pair<const unsigned , std::unique_ptr<const WhisperHandler> > pair({0x5B,std::move(handler)});
handlers.insert(std::move(pair));
//...
{
const auto &chandlers=handlers;
auto handlerit(chandlers.find(0x5B1));
if(handlerit!=chandlers.end()){
handlerit->second->HandleWhisper();
}else{
//ERROR - UNKNOWN HANDLER.
}
}
return 0;
}
I would suggest however you're only going to get return on investment for all this polymorphic machinery if you're going to allow the registration of handlers dynamically either from different modules of the application or by dynamically loading libraries that register themselves on load.
If it's a single project application (which it appears to be) then the switch table dispatch will probably work fine.
Because applications tend to communicate using IDs of some kind OO can start to look cumbersome when it in practice it needs to take an ID, map it to a polymorphic handler and then call the handler. Logically you've done the ID to logic mapping twice!
Footnote: The trick of knocking out the lowest 4-bits is somewhat separate from these methods and (of course) slightly fragile if the lower 4 bits become relevant to determining the handler down the line.