You cannot cast a List
of one type to a List
of a different type.
And if you think about it, you would be glad that you can't. Imagine the havoc you could cause if it was possible:
interface ICustomRequired
{
}
class ImplementationOne : ICustomRequired
{
}
class ImplementationTwo: ICustomRequired
{
}
var listOne = new List<ImplementationOne>();
var castReference = listOne as List<ICustomRequired>();
// Because you did a cast, the two instances would point
// to the same in-memory object
// Now I can do this....
castReference.Add(new ImplementationTwo());
// listOne was constructed as a list of ImplementationOne objects,
// but I just managed to insert an object of a different type
Note, however, that this line of code is legal:
exampleList as IEnumerable<ICustomRequired>;
This would be safe, because IEnumerable
does not provide you with any means to add new objects.
IEnumerable<T>
is actually defined as IEnumerable<out t>
, which means the type parameter is Covariant.
Are you able to change the parameter of the function to IEnumerable<ICustomRequired>
?
Otherwise your only option will be to create a new List.
var newList = (exampleList as IEnumerable<ICustomRequired>).ToList();
or
var newList = exampleList.Cast<ICustomRequired>().ToList();
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