C# Interface too rigid

Question

I'm working with some legacy code and have this existing interface:

public interface IProcess
{
    IDTO Process(IDTO request);
}

There is then a factory with a huge switch statement returning objects (17 of them) that implement the interface. The created objects then call process like:

return xProcess.Process(requestDTO);

My problem is that I now need to change a few of these to pass in a second parameter like:

xProcess.Process(requestDTO, Id);

I'm looking for an elegant way to achieve this.

I have tried making the interface an abstract class like:

public abstract class IProcess
{

    public virtual IDTO Process(IDTO request)
    {
       return null;
    }

    public virtual IDTO Process(IDTO request, int Id)
    {
        return null;
    }
}

This allows me to override the Process method in the created classes but I have a problem that IProcess is inherited by another interface, which is now obviously broken.

The legacy platform is huge and the test coverage is not great so I'm looking for a nice elegant solution with the minimum impact to the rest of the code base. Perhaps, there is a pattern I'm overlooking?

Can anyone help please? (examples would be great)

Thanks

David

Answer 1

Can you not create a new interface that inherits from the existing one, like

public interface IProcess2 : IProcess
{
    IDTO Process(IDTO request, int Id);
}

Then change your classes to inherit from the new one.

This should stop any users of the existing IProcess from breaking.