Static field initializers in c#

Question

I have following code in c#

class Test
{
  public static int X = Y;    
  public static int Y = 3;    
}

static void Main()
{
Console.WriteLine(Test.X);
Console.WriteLine(Test.Y);
}

In this case I am getting 0 and 3 but in the following case I am getting 3,3

class Test
{
  public static int X = 3;    
  public static int Y = X;    
}

static void Main()
{
Console.WriteLine(Test.X);
Console.WriteLine(Test.Y);
}

why is it so?

Answer 1

From the C# spec:

The static field variable initializers of a class correspond to a sequence of assignments that are executed in the textual order in which they appear in the class declaration.

Therefore, in your first snippet, since Y isn't initialized yet when X is, X has to default to 0 (because default(int) == 0). On the other hand, in your second snippet, Y can be initialized to the value of X because X has already been given a value of 3 in the immediately-preceding statement.

Answer 2

This is per the specification, which states the order for which static fields are initialized. The basic point is that they are initialized in the order that they are declared.

Consequently, in your first snippet, X is initialized first and then Y. As Y has not been initialized yet, it has the default value of 0 and so X gets the value 0.

In your second snippet, X is initialized first but is given the explicit value of 3. Then, Y is initialized and is given the value of X which is 3 since it was initialized first.

From §10.5.5.1 Static field initialization

The static field variable initializers of a class correspond to a sequence of assignments that are executed in the textual order in which they appear in the class declaration. If a static constructor (§10.12) exists in the class, execution of the static field initializers occurs immediately prior to executing that static constructor.