Question

I know that C# supports covariance in arrays like this :

object[] array = new string[3]; 

But I’m getting an error when it tries to compile the below code

class Dummy<K,T> where T:K {     public void foo()     {         K[] arr = new T[4];     } } 

It says ‘Cannot implicitly convert type ‘T[]’ to ‘K[]’ ‘

Why I’m getting this error ???

Answer 1

You have to specify that both T and K are reference types. Array covariance only works with reference types. Change the declaration to:

class Dummy<K,T> where T : class, K 

and it works fine. You don’t have to specify that K is a reference type, because if T is a reference type and it derives from or implements K, then K must be a reference type too. (At least I assume that’s the reasoning. It doesn’t hurt to add where K : class as well for clarity.)