列表＆lt; Of T＆gt;在.NET 3.0中有所区别？

Dictionary<,>

null

List<Foo> foos  = ...
Dictionary<Foo, bool> dict = new Dictionary<Foo, bool>();

foreach(Foo foo in foos)
   dict[foo] = true;

ICollection<Foo> distinctFoos = dict.Keys;

null

public static IEnumerable<T> Distinct<T>(IEnumerable<T> source)
{
    if (source == null)
        throw new ArgumentNullException("source");

    Dictionary<T, bool> dict = new Dictionary<T, bool>();
    bool nullSeen = false;

    foreach (T item in source)
    {
        if (item == null)
        {
            if (!nullSeen)
                yield return item;

            nullSeen = true;
        }

        else if (!dict.ContainsKey(item))
        {
            dict.Add(item, true);
            yield return item;
        }
    }
}

IEnumerable(Of T)

Distinct