C# – 9.0

By | 16/06/2021

In this post, we will see two interesting features introduced with C# 9.0.
For the complete list of all new features, we can go to Microsoft web site.

RECORDS
Records provide an extremely fast way to define an immutable object with value type semantics.

using System;
namespace csharp_9
{
    class Program
    {
        // Definition of a record
        private record user(Guid Id, string UserName, string Password);
        
        static void Main(string[] args)
        {
            var userOne = new user(Guid.NewGuid(), "UserName1", "Password1");
            Console.WriteLine(userOne);
        }
    }
}



If we run the application, this will be the result:

A Record is immutable in fact, if we try to change a value in userOne, we will receive a compile error:

In order to make userOne mutable, we have to define in different way the record User:

using System;
namespace csharp_9
{
    class Program
    {
        // Definition of a record
        private record user(Guid Id, string UserName, string Password)
        {
            public Guid Id { get; set; } = Id;
            public string UserName { get; set; } = UserName;
            public string Password { get; set; } = Password;
        }

        static void Main(string[] args)
        {
            var userOne = new user(Guid.NewGuid(), "UserName1", "Password1");
            Console.WriteLine(userOne);

            userOne.Password = "NewPassword";
            Console.WriteLine(userOne);
        }
    }
}



And now, if we run the application, this will be the result:

Obviously, we can decide which parameter we want to make mutable:

using System;

namespace csharp_9
{
    class Program
    {
        // Definition of a record
        private record user(Guid Id, string UserName, string Password)
        {
            public string Password { get; set; } = Password;
        }

        static void Main(string[] args)
        {
            var userOne = new user(Guid.NewGuid(), "UserName1", "Password1");
            Console.WriteLine(userOne);

            userOne.UserName = "NewUser";
            userOne.Password = "NewPassword";
            Console.WriteLine(userOne);
        }
    }
}



In this case, we will have a compile error, because UserName is immutable.

If we want to create a new Record from another one, we have to use the ” with ” command:

using System;
namespace csharp_9
{
    class Program
    {
        // Definition of a record
        private record user(Guid Id, string UserName, string Password);

        public static void Main(string[] args)
        {
            var userOne = new user(Guid.NewGuid(), "UserName1", "Password1");
            Console.WriteLine(userOne);

            var userTwo = userOne with { UserName = "UserName2", Id = Guid.NewGuid() };

            Console.WriteLine(userTwo);
        }
    }
}



If we run the application, this will be the result:

INIT ONLY SETTERS
With “Init Only Setters” we can decide to initialise a property only in the constructor:

using System;

namespace csharp_9
{
    class Program
    {
        public static void Main(string[] args)
        {
            var userAdmin = new Admin(Guid.NewGuid(), "UserAdmin1", "Password123");
            Console.WriteLine($"{userAdmin.Id} - {userAdmin.UserName} - {userAdmin.Password}");

            userAdmin.Password = "Password456";
            Console.WriteLine($"{userAdmin.Id} - {userAdmin.UserName} - {userAdmin.Password}");
        }
    }

    class Admin
    {
        public Guid Id { get; init; }
        public string UserName { get; init; }
        public string Password { get; set; }

        public Admin(Guid id, string userName, string password)
        {
            Id = id;
            UserName = userName;
            Password = password;
        }
    }
}



If we run the application, this will be the result:

But, if we try to change a property defined as “init”, we will have a compile error:



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