Undefined reference error when array size is given

[tcak via Digitalmars-d-learn]

Code is as follows:

main.d
=========================
import core.sys.posix.poll;
void main(){
        core.sys.posix.poll.pollfd[2] pollList;
}
=========================


Error:
main.d:(.text._Dmain+0x15): undefined reference to 
`_D4core3sys5posix4poll6pollfd6__initZ'


Remove "2" and it works.

main.d
==========================
import core.sys.posix.poll;

void main(){
        core.sys.posix.poll.pollfd[] pollList;
}
=========================


The error points to "__init". Struct is defined very simply.

    struct pollfd
    {
        int     fd;
        short   events;
        short   revents;
    }


I defined same struct in main file, and defined a similar array. 
There is no problem with that.

main.d
=========================
import core.sys.posix.poll;

struct pollfd2
{
    int     fd;
    short   events;
    short   revents;
}

void main(){
        core.sys.posix.poll.pollfd[] pollList;

        pollfd2[2] blah;
}
=========================

What is the reason of this error exactly?