What does "static this()" outside of a class mean?

Question

I'm very well aware of static constructors, but what does it mean to have a static this() outside of a class?

import std.stdio;

static this(){

  int x = 0;

}


int main(){

  writeln(x); // error

  return 0;
}

And how do I access the variables define in static this() ?

Answer 1

It's a module constructor. That code is run once for each thread (including the main thread).

There are also module destructors as well as shared module constructors and destructors:

static this()
{
   writeln("This is run on the creation of each thread.");
}

static ~this()
{
   writeln("This is run on the destruction of each thread.");
}

shared static this()
{
   writeln("This is run once at the start of the program.");
}

shared static ~this()
{
   writeln("This is run once at the end of the program.");
}

The purpose of these is basically to initialise and deinitialise global variables.

Answer 2

This is the module constructor. You can read about them here: http://www.digitalmars.com/d/2.0/module.html

Obviously, you can't access x in your sample, because it's a module constructor's local variable, just as well as you couldn't have done it with a class constructor's one. But you can access module-scope globals there (and initialise them, which is what the module constructors are for).