Cannot convert from List to List

Question

I have a set up like this:

abstract class Foo {}
class Bar : Foo {}

and a method elsewhere of this form:

void AddEntries(List&l         


        

Answer 1

This is not allowed for a simple reason. Assume the below compiles:

AddEntries(new List());

void AddEntries(List list)
{
   // list is a `List` at run-time
   list.Add(new SomethingElseDerivingFromFoo()); // what ?!
}

If your code would compile, you have an unsafe addition (which makes the whole generic lists pointless) where you added SomethingElseDerivingFromFoo to actually a List (runtime type).

To solve your problem, you can use generics:

void AddEntries(List list) where T:Foo
{

}