How to mutate the immutable state without a lot of mess and boilerplate

[lanwin]

So far so good. But how would you create and mutate the immutable state in C# without creating a lot of mess and boilerplate?

A few suggestions in the readme would be fantastic.

[GuillaumeSalles]

Hello lanwin,

Unfortunately, I did not found a silver bullet to get immutability without boilerplate in C# 6. But I can tell you what we do and where we want to go with immutability at my job.

• We use https://www.nuget.org/packages/System.Collections.Immutable for collections.
• We chose to not be strictly immutable to avoid too much boilerplate. We use a constructor with a parameter of the same type to avoid to reset every properties for every "With... methods". (If I remember well I found this trick in the Roslyn sources (large .NET project that heavily use immutability)).

    public class Customer
    {
        public string FirstName { get; private set; }

        public string LastName { get; private set; }

        public ImmutableList<Address> Addresses { get; private set; }

        public Customer()
        {

        }

        public Customer(Customer other)
        {
            this.FirstName = other.FirstName;
            this.LastName = other.LastName;
            this.Addresses = other.Addresses;
        }

        public Customer WithFirstName(string firstName)
        {
            return new Customer(this) { FirstName = firstName };
        }

        public Customer WithLastName(string lastName)
        {
            return new Customer(this) { LastName = lastName };
        }

        public Customer WithAddresses(ImmutableList<Address> addresses)
        {
            return new Customer(this) { Addresses = addresses };
        }
    }

• We use code snippets to generate "With... methods" faster. A code generator like the one used to generate the xaml.g.cs would be better... It would be awesome !
• A mutable state are usually spotted really fast through code review. If it is not enough, a custom Analyser could validate if a class is immutable or not and break the build if needed. We really did not need to go that far at my job.
• Wait for C# 7 immutable type ? https://github.com/dotnet/roslyn/issues/159

If those tips help you, I will update the readme in the few next days.

[GuillaumeSalles]

Maybe you will find the last C# 7 design notes interesting.

[GuillaumeSalles]

The new C# records could be useful to build an immutable state without boilerplate !

[xaviergonz]

For anyone who is interested I made something to minimize the boilerplate needed when using redux (at least while C# doesn't implement it itself):

https://github.com/xaviergonz/T4Immutable
T4Immutable is a T4 template for C# .NET apps that generates code for immutable classes.

As an extra note I just updated it to properly support properties that are collections. GetHashCode, Equals, etc will work OK as long as the collections are equivalent.