Magic value (number, string, etc)

Magic strings or any other magic values¶

Bad:

int responseCode = GetDeviceResponse();
if (responseCode == 188) {
    ...
}

Good (this can be reused elsewhere):

const int NoConnection = 188;
int responseCode = GetDeviceResponse();
if (responseCode == NoConnection) {
    ...
}

Bad:

public class MagicValues
{
    public void AcceptCard()
    {
        var d = new Device();
        d.SendCommand(1);
        d.SendCommand(2);
        d.SendCommand(9);
    }

    public void DispenseCard()
    {
        var d = new Device();
        d.SendCommand(1);
        d.SendCommand(3);
        d.SendCommand(9);
    }
}

Without magic values:

public class NoMagic
{
    private const int Initialize = 1;
    private const int Terminate = 9;

    public void AcceptCard() {
        var d = new Device();
        d.SendCommand(Initialize);
        d.SendCommand(2);
        d.SendCommand(Terminate);
    }

    public void DispenseCard()
    {
        var d = new Device();
        d.SendCommand(Initialize);
        d.SendCommand(3);
        d.SendCommand(Terminate);
    }
}

Good:

public class NoDuplicateLogic {
    private const int Initialize = 1;
    private const int Terminate = 9;

    public void AcceptCard() {
        ExecuteCommand(2);
    }

    public void DispenseCard()
    {
        ExecuteCommand(3);
    }

    private void ExecuteCommand(byte command)
    {
        var d = new Device();
        d.SendCommand(Initialize);
        d.SendCommand(command);
        d.SendCommand(Terminate);
    }
}