Need something like static inheritance in C#

Question

I'm having a small design issue and wanted to consult. Lets say we have the following class hierarchy:

abstract class A
{
}

class B : A
{
}

class C: A
{
}

I want that both B and C have a certain field x so that it's value is different between the classes but shared among all instances of the same class (i.e: if b1, b2 are instances of B and c1,c2 instances of C then b1.x = b2.x and c1.x = c2.x and b1.x != c1.x). Is there an elegant way to do this by taking advantage of the fact that both B, C derive from the same base class or do I have to create a static field x in both classes?

Thanks in advance.

Answer 1

You mean like this?

abstract class A
{
    static Dictionary<Type, int> all_x;
    protected int X {
        get { return all_x[GetType()]; }
        set { all_x[GetType()] = value; }
    }
}

---

If it has to be a field so you can pass by reference:

abstract class A
{
    class SharedType { int x; }
    static Dictionary<Type, SharedType> all_shared;
    protected SharedType Shared {
        get
        {
            Type t = GetType();
            SharedType result;
            if (!all_shared.TryGetValue(t, out result) {
                 result = new SharedType();
                 all_shared.Add(t, result);
            }
            return result;
        }
    }
}

---

Also, we can improve performance by doing the lookup only once per instance:

abstract class A
{
    class SharedType { int x; }
    static Dictionary<Type, SharedType> all_shared;
    protected SharedType Shared;
    A() {
        Type t = GetType();
        if (!all_shared.TryGetValue(t, out Shared) {
             Shared = new SharedType();
             all_shared.Add(t, Shared);
        }
    }
}