Question

I am defining a geenral API which will have a number of more specific derivations and want to know if C# interfaces are powerful enough to model this, and if so how, and if not how else I might model this.

To illustrate what I am trying to do imagine an authentication API with a general interface with an Authenticate function which takes an abstract AuthenticationToken. I want to then create more specific forms of this interface with as shown ..

abstract class AuthenticationToken
{
}

interface IAthentication
{
    bool Authenticate(string name, AuthenticationToken token);
}

class DoorKey : AuthenticationToken
{
}

interface IDoorAthentication : IAthentication
{
    bool Authenticate(string name, DoorKey token);
}

class DoorUnlocker : IDoorAthentication
{

    public bool Authenticate(string name, DoorKey token)
    {
    }
}

My intention is that the derived interface is constrained to comply with the high level form but that is not how C# interprets this.

Best Regards

Help me John Skeets .. you’re my only hope.
(Sorry .. my Star Wars BluRays have arrived!)

Answer 1

This is what you want:

abstract class AuthenticationToken
{
}

interface IAthentication<T> where T : AuthenticationToken
{
    bool Authenticate(string name, T token);
}

class DoorKey : AuthenticationToken
{
}

interface IDoorAthentication : IAthentication<DoorKey>
{
}

class DoorUnlocker : IDoorAthentication
{
    public bool Authenticate(string name, DoorKey token)
    {
    }
}

Generics with constraints!