qr-generate.pl

use strict;
use warnings;

{
  package QROverload;
  use overload 'qr' => sub {
    my $self = shift;
    qr/(??{ $self->_as_qr($_) })/;
  };

  sub new {
    my $class = shift;
    my $self = bless {}, $class;
  }

  sub _as_qr {
    my $self = shift;
    warn "generating qr for: $_[0]";
    $_[0] = "garf";
    qr/./;
  }
}

my $f = QROverload->new;

my $foo = "qwe";
my $g = $foo =~ $f;
warn $foo;
warn $g;