Question

I would like to initialize an object of type B from another class A, why I still get null? Is it possible to do it without using ref and out modifiers?

    class A
    {
        public void Initialize(B value)
        {
            if (value == null)
            {
                value = new B();
            }
        }
    }

    class B
    {

    }

    class Program
    {
        static void Main(string[] args)
        {
            A a = new A();
            B b = null;
            a.Initialize(b);
        }
    }

[upd.] I thought the b variable could be passed by ref because of it’s the instance of the class.

Answer 1

It is possible, just make Initialize() a function:

class A
{
    public B Initialize(B value)
    {
        if (value == null)
        {
            value = new B();
        }
        return value;
    }
}

And call it like:

    static void Main(string[] args)
    {
        A a = new A();
        B b = null;
        b = a.Initialize(b);
    }

This is a good solution, the data flow is clearly visible. No surprises.

But otherwise, just use a ref (not an out) : public void Initialize(ref B value) and call a.Initialize(ref b);

---

I thought the b variable could be passed by ref because of it’s the instance of the class.

To answer that you need very precise wording: b is not the instance of a class. b is a reference to an instance. Instances never have a name.

And b is treated just like a value type: the reference is passed by value to the method. Unless you use ref.