Question

I have a method who merge two lists. The two merged lists are lists of subtypes objects of the returned list. By “merging” I mean “Allowing duplicates”.

So Sub1 and Sub2 types are subtypes from Sup1 type.

Here is my code

var listSub1 = new List<Sub1>(); //With some content added..
var listSub2 = new List<Sub2>(); //With content too..  
var listToReturn = new List<Sup1>();
listToReturn.AddRange(listSub1.Select(item => item as Sup1).ToList());
listToReturn.AddRange(listSub2.Select(item => item as Sup1).ToList());

return listeToReturn;

It is working fine but I wonder if it is the best way to merge and cast the lists.

Answer 1

you could write

var newList = 
  listSub1.Cast<Sup1>()
  .Concat(listSub2.Cast<Sup1>()).ToList();

Note that Union is not correct to be used, since it will make sure that objects that are “equal” will come out only once.