public static TSource First <TSource>(IEnumerable <TSource> source)
{
if (source == null)
{
throw ThrowHelper.ArgumentNull("source");
}
IList <TSource> list = source as IList <TSource>;
if (list == null)
{
using (IEnumerator <TSource> enumerator = source.GetEnumerator())
{
if (!enumerator.MoveNext())
{
throw ThrowHelper.NoElements();
}
else
{
return(enumerator.Current);
}
}
}
else if (list.Count > 0)
{
return(list[0]);
}
throw ThrowHelper.NoElements();
}
