How to add an apple delegate to a list of fruit delegates?
class Testy
{
    public delegate void FruitDelegate<T>(T o) where T : Fruit;

    private List<FruitDelegate<Fruit>> fruits = new List<FruitDelegate<Fruit>>();

    public void Test()
    {
        FruitDelegate<Apple> f = new FruitDelegate<Apple>(EatFruit);

        fruits.Add(f); // Error on this line
    }

    public void EatFruit(Fruit apple) { }
}

The best overloaded method match for 'List<FruitDelegate<Fruit>>.Add(FruitDelegate<Fruit>)' has some invalid arguments`

FruitDelegate<Fruit> f = new FruitDelegate<Fruit>(EatFruit);
f(new Apple());
f(new Banana());

public delegate void FruitDelegate<in T>(T o) where T : Fruit;

FruitDelegate<Apple> f = new FruitDelegate<Fruit>(EatFruit);
f(new Apple());

FruitDelegate<Fruit> f = new FruitDelegate<Apple>(EatApple); // invalid
f(new Apple());
f(new Banana());