Question

Something like this should be possible in C#, right?

    public void Start ()
    {
        Class1 x = new Class1 ();

        string s = Something (x);

        Console.ReadKey ();
    }

    public string Something (IInterface obj)
    {
        return foo (obj);  //  <-- Problem line
    }

    public string foo (Class1 bar)
    {
        return "Class1";
    }

    public string foo (Class2 bar)
    {
        return "Class2";
    }

    interface IInterface {}

    class Class1 : IInterface {}

    class Class2 : IInterface {}

Answer 1

No. Your foo methods expect either Class1 or Class2. You’re passing an IInterface which could be either Class1 or Class2. It won’t compile because the compiler doesn’t know which overloaded method to call. You would have to cast it to one of the types to get it to compile.

Alternatively, IInterface would hold the foo method that took no arguments and returned which class it was. Then something could take the IInterface object and call obj.foo()

Like:

interface IInterface 
{ 
    public string foo(); 
}

class Class1 : IInterface
{
     public string foo()
     {
         return "Class1";
     }
}

class Class2 : IInterface
{
     public string foo()
     {
         return "Class2";
     }
}

public void Something(IInterface obj)
{
    return obj.foo();
}