static initialization of associative arrays

[Tyro[a.c.edwards]]

Is it yet possible to statically initialize an associative array? If so, 
please point me to the documentation. I am using DMD v2.028.

Currently I'm able to do this:
import std.stdio;

string[string] types;
static this(){
    types = [ "void":"void", "bool":"bool" ];
}

void main(){
    writeln(types);
}

Output = [void:void,bool:bool] which is exactly what I want.

However, removing static this() results in an error.

string[string] types = [ "void":"void", "bool":"bool" ];

Result:
api.d(77): Error: non-constant expression ["void":"void","bool":"bool"]

How do I make the initialization constant?

Thanks,
Andrew