To interface or not to interface

[Kagamin]

> ICollection<A> acoll;
> ICollection<B> bcoll;
> A[] cat;
> ICollection<A>.CopyTo(A[],int)
> ICollection<B>.CopyTo(B[],int) - note the signature, the destination array can't be an array of supertype. There's no chance to throw an exception because the code doesn't pass type check at compile time.

To ease understanding:

ICollection<Animal> acoll;
ICollection<Cat> ccoll;
Animal[] animals;
ICollection<Animal>.CopyTo(Animal[],int)
ICollection<Cat>.CopyTo(Cat[],int)