/// <summary>
/// The sum of a sequence, with a delegate returning an integer
/// for each element of the sequence.
/// </summary>
public static int Sum <TIn, TOut, TProducer>(
this SpanEnumerable <TIn, TOut, TProducer> spanEnum,
Func <TOut, int> getValue)
where TProducer : struct, IProducer <TIn, TOut>
=>
spanEnum.Select(getValue).Sum();
/// <summary>
/// The sum of a sequence, with a delegate returning an integer
/// for each element of the sequence.
/// </summary>
public static int Sum <TOut>(
this SpanEnumerable <TOut> spanEnum,
Func <TOut, int> getValue)
=>
spanEnum.Select(getValue).Sum();