Protect Your Immutable Object Invariants

ViolateImmurable.cs

 public class Student
    {
        public readonly string Name;

        public readonly string Email;

        public readonly List<String> Subjects;

        public Student(string name, string email, List<String> subjects)
        {
            this.Name = name;
            this.Email = email;
            this.Subjects = subjects;
        }

        public override string ToString()
        {
            return ToDisplayString();
        }

        public string ToDisplayString()
        {
            return $"Name: {Name}, Email: {Email}, Subjects: {string.Join(", ", Subjects)}";
        }
    }

    internal class AnotherProgram
    {
        private static void Main(string[] args)
        {
            List<string> studentSubjects = new List<string> { "Maths", "English", "Physics" };
            Student author = new Student("John Doe", "[email protected]", studentSubjects);
            Console.WriteLine(author);
            
            // Oh, dear. We are able to change the subjects even after instantiation.
            author.Subjects.Add("Chemistry");
            Console.WriteLine(author);
        }
    }