public static TSource Single <TSource>(this IEnumerable <TSource> source)
{
if (source == null)
{
ThrowHelper.ThrowArgumentNullException(ExceptionArgument.source);
}
if (source is IList <TSource> list)
{
switch (list.Count)
{
case 0:
ThrowHelper.ThrowNoElementsException();
return(default);
case 1:
return(list[0]);
}
}
else
{
using (IEnumerator <TSource> e = source.GetEnumerator())
{
if (!e.MoveNext())
{
ThrowHelper.ThrowNoElementsException();
}
TSource result = e.Current;
if (!e.MoveNext())
{
return(result);
}
}
}
ThrowHelper.ThrowMoreThanOneElementException();
return(default);
