using System;

using System.Linq;

using System.Collections.Generic;

​

public class Program

{

    public static void Main()

    {

        // enumerable used in all examples

        var arr = new[] { "Zero", "One", "Two", "Three", "Four", "Five" };

        // Accessing the "index" of an enumerable within a foreach

        Console.WriteLine("Example One - Accessing indices in foreach");

        foreach (var (str, idx) in arr.Select((idx, str) => (idx, str)))

        {

            Console.WriteLine($"idx={idx}, str={str}");

        }

        // Join an enumerable where the string is the delimiter.

        Console.WriteLine("\nExample Two - string join");

        Console.WriteLine(",".JoinEx(arr));

        // Downcasting with pattern matching,

        // when succesful then downCasted will be populated

        // and when unnsuccessful it will be null. 

        Console.WriteLine("\nExample Three - pattern matching");

        BaseClass downCastMe = new DerivedClass();

        if (downCastMe is DerivedClass downCasted)

        {

            Console.WriteLine(downCasted.IsBase());

        }

        else

        {

            Console.WriteLine($"Not {nameof(DerivedClass)}");

        }

        // Iterating with ranges, which is start inclusive and end exclusive

        // e.g. this prints Two, Three, Four which are indices 2, 3, 4 of arr.

        Console.WriteLine("\nExample Four - enumerable ranges");

        foreach (var obj in arr[2..5])

        {

            Console.WriteLine(obj);

        }

        Console.WriteLine("\nDone!");

    }

}

​

// string extension allowing something like: 

// ",".JoinEx(arr);

// Which will comma separate the input enumerable

public static class StrExtensions

{

    public static string JoinEx(this string separator, IEnumerable<string> input) => string.Join(separator, input);

}

​

// Classes showing example of downcasting with pattern matching

public class BaseClass

{

    public virtual bool IsBase() => true;

}

​

public class DerivedClass : BaseClass

{

    public override bool IsBase() => false;

}