Casting of Generic List to a Class derived from a List

Question

I created a class derived from List. However when I tried casting the class to another List object I get a runtime error. My code is similar to the one posted below:

Answer 1

You can use this Extension Method

public static M Cast(this IEnumerable input) where M : ICollection, new()
{
  var ret = new M();
  foreach(var item in input?? Enumerable.Empty())
  {
    ret.Add(item);
  }
  return ret;
}

then you can use it like

var qry = (from c in db.Categories
   select new CategoryObj
   {
       CategoryID = c.CategoryID,
       CategoryName = c.CategoryName,
       Description = c.Description
    }).Cast()