Why won't this static variable increment when using generics?

Question

I need a certain class to contain a static member that keeps track of everytime an instance of that class is instantiated, essentially so that each instance of the class has a unique index. It works with a non-generic class but this generic implementation fails whenever the type T differs between instances:

class A<T> {    private static int counter;     private static int Counter {        get {            Increment();            return counter;         }    }     private static void Increment() {        counter++;     }     public int Index;      public A()    {        this.Index = Counter; // using A<T>.Counter makes no difference         Console.WriteLine(this.Index);          } }   class Program {     static void Main(string[] args)     {         var a = new A<string>();         var b = new A<string>();          var c = new A<string>();         var d = new A<int>();      } } 

The output is:

1

2

3

1

As soon as the type T switches to int instead of string, the counter resets.

Does this fail by design, and if so what is the reason or how can I get around it? Or is it a bug? It makes sense to some degree because the type T, being generic, is in the class declaration, but..

Answer 1

Each different T creates a new class for A<T> and hence distinct static counters.

To get around this you can use inheritance like so:

abstract class A {    protected static int counter; }  class A<T> : A {    private static int Counter {        get {            Increment();            return counter;         }    }     private static void Increment() {        counter++;     }     public int Index;      public A()    {        this.Index = Counter;         Console.WriteLine(this.Index);          } }