How can I make the following code work? I don't think I quite understand C# generics. Perhaps, someone can point me in the right direction.
public abstract class A
{
}
public class B : A
{
}
public class C : A
{
}
public static List<C> GetCList()
{
return new List<C>();
}
static void Main(string[] args)
{
List<A> listA = new List<A>();
listA.Add(new B());
listA.Add(new C());
// Compiler cannot implicitly convert
List<A> listB = new List<B>();
// Compiler cannot implicitly convert
List<A> listC = GetCList();
// However, copying each element is fine
// It has something to do with generics (I think)
List<B> listD = new List<B>();
foreach (B b in listD)
{
listB.Add(b);
}
}
It's probably a simple answer.
Update:
First, this is not possible in C# 3.0, but will be possible in C# 4.0.
To get it running in C# 3.0, which is just a workaround until 4.0, use the following:
// Compiler is happy
List<A> listB = new List<B>().OfType<A>().ToList();
// Compiler is happy
List<A> listC = GetCList().OfType<A>().ToList();
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