Order of static constructors/initializers in C#

Question

While working on a C# app I just noticed that in several places static initializers have dependencies on each other like this:

static private List         


        

Answer 1

It seems to depend on the sequence of lines. This code works:

static private List a = new List() { 1 };
static private List b = new List() { a[0] };

while this code does not work (it throws a NullReferenceException)

static private List a = new List() { b[0] };
static private List b = new List() { 1 };

So, obviously no rules for cyclical dependency exist. It's peculiar however that the compiler does not complain...

---

EDIT - What's happening "across files"? If we declare these two classes:

public class A {
    public static List a = new List() { B.b[0] };
}
public class B {
    public static List b = new List() { A.a[0] };
}

and try to access them with this code:

try { Console.WriteLine(B.b); } catch (Exception e) { Console.WriteLine(e.InnerException.Message.); }
try { Console.WriteLine(A.a); } catch (Exception e) { Console.WriteLine(e.InnerException.Message); }
try { Console.WriteLine(B.b); } catch (Exception e) { Console.WriteLine(e.InnerException.Message); }

we are getting this output:

The type initializer for 'A' threw an exception.
Object reference not set to an instance of an object.
The type initializer for 'A' threw an exception.

So the initialization of B causes an exception in static constructor A and lefts field a with the default value (null). Since a is null, b can not also be initialized properly.

If we do not have cyclical dependencies, everything works fine.

---

EDIT: Just in case you didn't read the comments, Jon Skeet provides a very interesting reading: The differences between static constructors and type initializers.