/// <summary>
/// The normal mechanism for building up an ImmutableSet is to start with Empty and call Add
/// repeatedly. However, if you already know that you're going to add all the elements of
/// an existing enumerable (a common pattern), then do everything in one step.
/// </summary>
/// <remarks>
/// As a bonus, we can skip creation of a bunch of temporary set objects and ensure that Empty
/// is the only zero-element instance.
/// </remarks>
public static ImmutableHashSet <T> From <T>(IEnumerable <T> values)
{
if (values == null)
{
throw new ArgumentNullException("values");
}
ImmutableDictionary <T, object> map = ImmutableDictionary.Create <T, object>(values.Select(v => new KeyValuePair <T, object>(v, null)));
return(map.Count > 0
? ImmutableHashSet <T> .PrivateCtor_DONOTUSE(map)
: ImmutableHashSet <T> .PrivateEmpty_DONOTUSE());
}
