use warnings;
use strict;
#use re 'debug';

my $str = "foobar";

sub getit {
	print "Getit! pos=",pos($str)//"undef","\n";
	return qr/[aeiou]/i;
}

print "### haukex\n";
print "Matches: <", $str=~/(??{getit})/g, ">\n";

print "### jwkrahn\n";
my $reg_str = getit();
print "Matches: <", $str=~/$reg_str/g,    ">\n";

print "### Eily\n";
print "Matches: <", $str=~/@{[getit]}/g,  ">\n";

__END__

### haukex
Getit! pos=0
Getit! pos=1
Getit! pos=2
Getit! pos=3
Getit! pos=4
Getit! pos=5
Getit! pos=6
Matches: <ooa>
### jwkrahn
Getit! pos=undef
Matches: <ooa>
### Eily
Getit! pos=undef
Matches: <ooa>