I wrote a program that allow two classes to "fight". For whatever reason C# always wins. What's wrong with VB.NET?

Question

I wrote a program that allow two classes to "fight". For whatever reason C# always wins. What's wrong with VB.NET ?

   static void Main(string[] args)
    {
        Player a = new A();
        Player b = new B();

        if (a.Power > b.Power)
            Console.WriteLine("C# won");
        else if (a.Power < b.Power)
            Console.WriteLine("VB won");
        else
            Console.WriteLine("Tie");
    }

Here are the players: Player A in C#:

public class A : Player
{
    private int desiredPower = 100;

    public override int GetPower
    {
        get { return desiredPower; }
    }
}

Player B in VB.NET:

Public Class B
   Inherits Player

   Dim desiredPower As Integer = 100

   Public Overrides ReadOnly Property GetPower() As Integer
       Get
          Return desiredPower
       End Get
   End Property
 End Class

And here is a base class.

public abstract class Player
{
    public int Power { get; private set; }

    public abstract int GetPower { get; }

    protected Player()
    {
        Power = GetPower;
    }
}

Answer 1

The issue here is that VB is calling the base constructor before setting its field value. So the base Player class stores zero.

.method public specialname rtspecialname 
        instance void  .ctor() cil managed
{
  // Code size       15 (0xf)
  .maxstack  8
  IL_0000:  ldarg.0
  IL_0001:  call       instance void [base]Player::.ctor()
  IL_0006:  ldarg.0
  IL_0007:  ldc.i4.s   100
  IL_0009:  stfld      int32 B::desiredPower
  IL_000e:  ret
} // end of method B::.ctor

Answer 2

Promoting my comments to an answer:

Me:

Try writing each "power" to the console as well

Prankster:

C#: 100 VB.NET: 0

Me:

As I suspected. Looks like VB.Net is calling the Base constructor before the inherited constructor, and therefore VB's desiredPower variable is still 0, whereas C# does it in reverse (remember, literal initialization happens at the end of the constructor).

Update:
I wanted to find some documentation on the behavior (otherwise you're looking at behavior that might change out from under you with any new .Net release). From the link:

The constructor of the derived class implicitly calls the constructor for the base class

and

Base class objects are always constructed before any deriving class. Thus the constructor for the base class is executed before the constructor of the derived class.

Those are on the same page and would seem to be mutually exclusive, but I take it to mean the derived class constructor is invoked first, but it is assumed to itself invoke the base constructor before doing any other work. Therefore it's not constructor order that important, but the manner in which literals are initialized.

I also found this reference, which clearly says that the order is derived instance fields, then base constructor, then derived constructor.

Answer 3

This happens because C# first initialize class fields, and than call base constructors. VB instead does the opposite, so when in VB you assign your value to Power, private field is not yet initialized and its value is 0.

Answer 4

By the time the constructor on B completes, both players will have a theoretical value of 100 in their private members.

However because of the superior internals of C#, the CLI generally considers integers and other primitive values values compiled from that language to be higher, and those from VB.NET to be lower, even when they contain the same bits.