Question

I have a very simple scenario : a “person” can be a “customer” or an “employee” of a company.

A “person” can be called by phone with the “Call” method.

Depending on which role the “person” plays in the context of the call, e.g. the announcement of a new product or the announcement of a change in organization, we should either use the phone number provided for the “customer” role or the one provided for the “employee” role.

Here is a sum-up of the situation :

interface IPerson
{
    void Call();
}

interface ICustomer : IPerson
{
}

interface IEmployee : IPerson
{
}

class Both : ICustomer, IEmployee
{
    void ICustomer.Call()
    {
        // Call to external phone number
    }

    void IEmployee.Call()
    {
        // Call to internal phone number
    }
}

But this code doe not compile and produces the errors :

error CS0539: 'ICustomer.Call' in explicit interface declaration is not a member of interface
error CS0539: 'IEmployee.Call' in explicit interface declaration is not a member of interface
error CS0535: 'Both' does not implement interface member 'IPerson.Call()'

Does this scenario has any chance to be implementable in C# in a different way or will I have to find another design ?

If so what alternatives do you propose ?

Thanks in advance for your help.

Answer 1

Your objective does not make sense.

Neither ICustomer nor IEmployee define a Call() method; they just inherit the method from the same interface. Your Both class implements the same interface twice.
Any possible Call call will always call IPerson.Call; there are no IL instructions that will specifically call ICustomer.Call or IEmployee.Call.

You may be able to solve this by explicitly redefining Call in both child interfaces, but I highly recommend that you just give them different names.