Question

Suppose you have the following class:

class Car : IPainting
{
 ...
}

Then a function like this:

void AddCars(IEnumerable<Car> collection)

Then a code snippet like this:

Car bmw = new Car();
Car mercedes = new Car();

IPainting a = (IPainting) bmw;
IPainting b = (IPainting) mercedes;

IPainting[] paintings = new IPainting[] {a, b};

AddCars(paintings); // fails to compile

This of course doesn’t compile because the AddCars() method accepts only a collection of Cars but it is what the ‘paintings’ array is made of.

I know that C# 4.0 will probably provide a solution for this. Is there any workaround today for it?

Thanks,

Alberto

Answer 1

C# 4 will not allow the code that you wrote, since the method AddCars expects an IEnumerable<Car> which implements IPainting. This does not mean that you can pass any class implementing IPainting (you could for instance have a class Bike : IPainting that has nothing to do with the Car class whatsoever. However, it will allow the other way around; if you have void AddCars(IEnumerable<IPainting> collection) you can pass a List<Car> to the method.

Until then, you will need to stick to passing Car sequences to the method, by using some casting mechanism (such as painting.Cast<Car>() suggested in other answers).