静态构造函数在实例构造函数之后调用？

Question

Dear all, the question like this one has been already asked , but among the answers there was no explanation of the problem which I see.

The problem: the C# Programming Guide says:

A static constructor is used to initialize any static data, or to perform a particular action that needs performed once only. It is called automatically before the first instance is created or any static members are referenced.

In particular, static constructor is called before any instance of a class is created. (This doesn't ensure that the static constructor finishes before creation of instance, but this is a different story.)

Let's consider the example code:

using System;

public class Test
{
    static public Test test = new Test();
    static Test()
    {
        Console.WriteLine("static Test()");
    }
    public Test()
    {
        Console.WriteLine("new Test()");
    }
}

public class Program
{
    public static void Main()
    {
        Console.WriteLine("Main() started");
        Console.WriteLine("Test.test = " + Test.test);
        Console.WriteLine("Main() finished");
    }
}

It outputs:

Main() started
new Test()
static Test()
Test.test = Test
Main() finished

So we can see that the instance constructor finishes (and thus an instance is created) before the static constructor starts . Doesn't this contradict the Guide? Maybe the initialization of static fields is considered to be an implicit part of static constructor?

Answer 1

Inline initializers for static fields run before the explicit static constructor.

The compiler transforms your class into something like this:

public class Test {
    .cctor {    //Class constructor
        Test.test = new Test();                //Inline field initializer
        Console.WriteLine("static Test()");    //Explicit static ctor
    }
    .ctor { ... }    //Instance constructor
}

Note that this is independent of the declaration order.

To quote the 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. If a static constructor (Section 10.11) exists in the class, execution of the static field initializers occurs immediately prior to executing that static constructor.