std.regexp and std.file listdir

[jicman]

I have this program:

import std.stdio;
import std.file;
import std.regexp;

int main(char[][] args)
{
  char[][] f = listdir(r"d:\tmp",RegExp(r"*.pdf","i"));
  writefln(f.length);
  return(0);
}

When I run it, I get,

Error: *+? not allowed in atom

Why?

thanks,

josé