using System;

class Hoge
{
    private string _helloWorld;
    private char _suffix = '!';

    public string HelloWorld
    {
        get => _helloWorld;
        set => _helloWorld = value ?? throw new ArgumentNullException();
    }

    public string TryGetHelloWorld(out string str)
        => str = (this.HelloWorld is string helloWorld) ? helloWorld : "";

    public ref char GetSuffix() => ref _suffix;
}

class Program
{
    public static void Main()
    {
        var hoge = new Hoge() { HelloWorld = "Hello World" };
        var suffix = hoge.GetSuffix();

        switch (hoge)
        {
            case object hogeObj:
            {
                ((Hoge)hogeObj).TryGetHelloWorld(out var helloWorld);
                Console.Write(helloWorld);
                Console.Write(suffix);
                break;
            }
        }
    }
}