using System;

using System.Collections.Generic;

using System.Linq;

​

public class Program

{

    public static void Main()

    {

        var list = new[] {'A','B','C'};

        foreach(var (el, i, isFirst, isLast) in list.Enumerate()) {

            Console.WriteLine($"el={el}, i={i}, isFirst={isFirst}, isLast={isLast}");

        }

        foreach(var (el, i, _, _) in list.Enumerate()) {

            Console.WriteLine($"el={el}, i={i}");

        }

        foreach(var (el, _, _, isLast) in list.Enumerate()) {

            Console.WriteLine($"el={el}, isLast={isLast}");

        }

        foreach(var entry in list.Enumerate()) {

            Console.WriteLine($"element={entry.element}, index={entry.index}");

        }

        foreach(var (el, isFirst, isLast) in list.EnumerateDetail()) {

            Console.WriteLine($"el={el}, isFirst={isFirst}, isLast={isLast}");

        }

    }

}

​

public static class ListExtensions

{

    public static IEnumerable<(T element, int index)> EnumerateIndex<T>(this IEnumerable<T> list) {

        return list.Select((el, i) => (el, i));

    }

    public static IEnumerable<(T element, int index, bool isFirst, bool isLast)> Enumerate<T>(this IEnumerable<T> list) {

        var len = list.Count();     

        return list.Select((el, i) => (el, i, i == 0, i == len -1));

    }

    public static IEnumerable<(T element, bool isFirst, bool isLast)> EnumerateDetail<T>(this IEnumerable<T> collection) {

        using var enumerator = collection.GetEnumerator();

        var isFirst = true;

        var isLast = !enumerator.MoveNext();

​

        while (!isLast)

        {

            var current = enumerator.Current;        

            isLast = !enumerator.MoveNext();

​

            yield return (current, isFirst, isLast);

            isFirst = false;

        }

    }

}