C# 中小型集合的 List.Add 与 HashSet.Add

Given

HashSet<T> set;
List<T> list;
T t;

其中哪一个对于小型集合表现更好？

if (! list.Contains (t)) list.Add (t);

Or

set.Add (t);

疑点来源：HashSet 与 List 性能对比 https://stackoverflow.com/questions/150750/hashset-vs-list-performance

It really has to do with how you are going to use the data structures. If you need to access an item using an index, then you can't use a HashSet, also if you need to store duplicates, you can;t use HashSet. A List is typically used for most operations, so I you don't understand the underlying design and functionality of the HashSet, then chances are a List will suffice.