static Option <TResult> ElementAtAt <TEnumerable, TEnumerator, TSource, TResult, TSelector>(this TEnumerable source, int index, TSelector selector)
where TEnumerable : IValueReadOnlyCollection <TSource, TEnumerator>
where TEnumerator : struct, IEnumerator <TSource>
where TSelector : struct, IFunction <TSource, int, TResult>
=> index < source.Count
? ValueEnumerableExtensions.ElementAtAt <TEnumerable, TEnumerator, TSource, TResult, TSelector>(source, index, selector)
: Option.None;
