Best practice when using C# 8.0 nullable reference types with deserialization?

Question

I am trying C# 8.0 out, and I want to enable the null reference checking for the entire project. I am hoping I can improve my code design, and without disabling the nullabil

Answer 1

While certainly highlighted due to non-nullable defaults in C# 8, this is really a common 'circular dependency' problem that has always existed with interdependent construction.

As you found, one standard solution is to use a restricted setter. With C# 8, you may want to use a 'null-forgiving' null! during deserialization of the object graph - allowing you to differentiate an unconstructed set from a valid empty set, and minimize allocation.

Example:

class Person
{
    internal Person(string name, IReadOnlyList friends)
    {
        Name = name; Friends = friends
    }

    public string Name { get; }
    public IReadOnlyList Friends {get; internal set;}
}

class SerializedPerson { ... }

IEnumerable LoadPeople(string path)
{
    var serializedPeople = LoadFromFile(path);

    // Note the use of null!
    var people = serializedPeople.Select(p => new Person(p.Name, null!));

    foreach(var person in people)
    {
        person.Friends = GetFriends(person, people, serializedPeople);
    }

    return people;
}