C# 형변환 is as 키워드

is는 객체가 해당 형식에 해당하는 지를 검사하여 bool 값을 결과로 반환.
as는 형 변환 연산자와 같은 역할을 하지만, 형변환 연산자가 변환에 실패하는 경우에는 예외를 던지는 반면, as 연산자는 객체 참조를 null로 만든다.

using System;
 
class Mammal{}
class Dog : Mammal{}
class Cat : Mammal{}
 
 
Mammal m1 = new Dog();
Dog dog;
Cat cat;
 
if(m1 is Dog)
{
    dog = (Dog)m1;
    Console.WriteLine("m1 is dog");
}
else
    Console.WriteLine("m1 is not dog");
 
if (m1 is Cat)
{
    cat = (Cat)m1;
    Console.WriteLine("m1 is cat");
}
else
    Console.WriteLine("m1 is not cat");
 
// m1 is dog
// m1 is not cat
 
 
Mammal m2 = new Cat();
dog = m2 as Dog;
cat = m2 as Cat;
 
if (dog)
    Console.WriteLine("m2 is dog");
 
else
     Console.WriteLine("m2 is not dog");
 
if (cat)
    Console.WriteLine("m2 is cat");
 
 else
     Console.WriteLine("m2 is not cat");
 
// m2 is not dog
// m2 is cat