Why can't I pass List as a parameter to a method that accepts List<object>?

Question

The following code gives me this error:

Cannot convert from \'System.Collections.Generic.List\' to \'System.Collections.Generic.List\'.

Answer 1

It's because a list of a class is not convertible to a list of the base class. It's a deliberate decision to make the language safe. This question gets asked often.

Here is my standard answer of how to work around the issue:

List listOfA = new List().ConvertAll(x => (A)x);

or:

List listOfA = new List().Cast().ToList();

Also here is really good explanation from Eric Lippert himself, one of the chief architects on the C# team.