C#派生属性在内部是如何工作的?它内部的方法什么时候被调用来作用于声明它们的类/方法/属性？

public class Person
{
    private string firstName;
    private string lastName;

    public string FirstName
    {
        get { return firstName; }
        set { firstName = value; }
    }

    public string LastName
    {
        get { return lastName; }
        set { lastName = value; }
    }

    // 派生属性 FullName
    public string FullName => $"{FirstName} {LastName}";
}

public class Program
{
    public static void Main()
    {
        var person = new Person();
        person.FirstName = "John";
        person.LastName = "Doe";

        // 访问派生属性 FullName
        Console.WriteLine(person.FullName); // 输出: John Doe
    }
}