C#: "$"作用和用法

 static void Main(string[] args)
        {
            string name = "波波";
            int age = 18;
            string str = string.Format("my name is{0}, I'm {1} years old", name, age);
            string str2 = $"my name is{name}, I'm {age} years old";
            string str3 = string.Format("Today is {0:D}", DateTime.Now);
            string str4 = $"Today is {DateTime.Now:D}";
            Console.WriteLine($"{str}");
            Console.WriteLine($"{str2}");
            Console.WriteLine($"{str3}");
            Console.WriteLine($"{str4}");
            Console.ReadKey();


        }