Question

I am trying to pass multiple generic interfaces as parameters to the constructor of one of my classes.

The following code does not compile:

public interface IPosterGenerator<T>
{
    IQueryable<T> GetPosters();
}

public class Pinboard
{
    public Pinboard(IPosterGenerator<A> firstPosterGenerator, IPosterGenerator<B> secondPosterGenerator, IPosterGenerator<B> thirdPosterGenerator)
    { 
    }
}

I have about a hundred different types of poster generators. They all inherit from the IPosterGenerator interface. When I instantiate a new Pinboard, I need to pass three IPosterGenerators to the pinboard’s constructor. However, every of these three IPosterGenerators will be of a different type. That’s why I came up with this silly A, B and C.

Can this be done at all?

Answer 1

It sounds like you probably want to make Pinboard generic:

public class Pinboard<T1, T2, T3>
{
    public Pinboard(IPosterGenerator<T1> generator1,
                    IPosterGenerator<T2> generator2,
                    IPosterGenerator<T3> generator3)
    {
         ...
    }
}

To make it easier to call, you can also create a non-generic class with a generic method:

public static class Pinboard
{
    public static Pinboard<T1, T2, T3> Create(IPosterGenerator<T1> generator1,
                                              IPosterGenerator<T2> generator2,
                                              IPosterGenerator<T3> generator3)
    {
        return new Pinboard<T1, T2, T3>(generator1, generator2, generator3);
    }
}

Then if you’ve already got the generators, you can just call:

// Or whatever...
var board = Pinboard.Create(bigGenerator, smallGenerator, mediumGenerator);