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