Demo of the problem¶

namespace SOLID.OCP.Violation
{
    public class DeviceFinder
    {
        SerialPort port = new SerialPort();
        switch (model)
        {
            case DeviceModel.BillAccepterCashCode:
                {
                    port.BaudRate = 9600;
                    port.Parity = Parity.Even;
                    port.Handshake = Handshake.RequestToSend;
                    return Find(port)
                }
            case DeviceModel.BillDispenserEcdm:
                {
                    port.BaudRate = 4800;
                    port.Parity = Parity.Mark;
                    port.Handshake = Handshake.RequestToSendXonXOff;
                    return Find(port)
                }
            case DeviceModel.CoinAccepterNri:
                {
                    port.BaudRate = 19200;
                    port.Parity = Parity.Odd;
                    port.Handshake = Handshake.XonXOff;
                    return Find(port);
                }
            case DeviceModel.CoinDispenserCube4:
                {
                    port.BaudRate = 9600;
                    port.Parity = Parity.Space;
                    port.Handshake = Handshake.None;
                    return Find(port);
                }
        }
    }
}

All this does is calls the find method. If a new case appears, we will need to modify the program. Often these [[switch case]]s start appearing in other places as well which will make these modifications even harder.

We can use Open-Closed Principle Refactorings.