C# Type-testing operator : is, as, typeof 연산자

is 연산자

지정된 형식과 호환되는지 확인

int i = 27;
object iBoxed = i;

Console.WriteLine(isBoxed is int);		// True
Console.WriteLine(isBoxed is long);		// False

---

as 연산자

지정된 형식으로 변환

IEnumerable<int> numbers = new List<int>() {10,20,30};
IList<int> indexable = numbers as IList<int>;

if(indexable != null)
{
	Console.WriteLine(indexable[0] + indexable[indexable.Count -1])	// 10 + 30 = 40
}

---

예제

using System;
using System.Collections;
using System.Collections.Generic;

public static class FlattenArray
{
    public static List<object> list = new List<object>();

    public static IEnumerable Flatten(IEnumerable input)
    {
        list.Clear(); // 여러 번 호출될 때 중복 방지
        dig(input);
        return list;
    }

    public static void dig(IEnumerable input)
    {
        foreach (var a in input)
        {
            if (a == null) continue;

            if (a is IEnumerable) // is 사용 안 함
            {
                IEnumerable nested = a as IEnumerable;
                dig(nested);
            }
            else
            {
                list.Add(a);
            }
        }
    }
}

https://exercism.org/tracks/csharp/exercises/flatten-array

Flatten Array in C# on Exercism