package lazydbvalue;

use strict;
use Carp;

sub TIESCALAR {
    # $sth is a prepared DBI statement handle
    my ($class, $sth) = @_;
    my $self = {};
    $self->{sth} = $sth;
    bless ($self, $class);
    return $self;
}

sub FETCH {
    my $self = shift;
    $self->{sth}->execute();
    my $row = $self->{sth}->fetchrow_arrayref;
    $self->{sth}->finish();
    return $row->[0];
}

sub STORE {
    my ($self, $sth) = @_;
    croak('STORE not supported - read only');
}

sub DESTROY {
    my $self = shift;
    undef $self->{sth};
}

package main;
use strict;
use DBI;

# Returns the "lazy" tied scalar
sub getNumUsers {
    my $dbh = shift;
    my $sth = $dbh->prepare('SELECT COUNT(*) FROM users');
    tie my $numUsers, 'lazydbvalue', $sth;
    return $numUsers;
}

# Connect to DB etc., assiging connection to $dbh;

my $numUsers = getNumUsers($dbh);

print "Number of users: $numUsers\n";

##</code><code>##

sub FETCH {
    my $self = shift;

    # Just passing...
    if ( justPassingTheValue() ) {
        return $self;
    }

    # Value is being used in some expression
    # Now evaluate the real thing...
    $self->{sth}->execute();
    my $row = $self->{sth}->fetchrow_arrayref;
    $self->{sth}->finish();
    return $row->[0];
}