# This snippet:
$item->subs(my_execer($SQL));

# is just another way of writing
my @tmp = my_execer($SQL);
$item->subs(@tmp)

# Here's the output
<snip>
printing weird stuff
1054226
426
$VAR1 = bless( [
                 1054226,
                 426,
                 []
               ], 'Item' );
@retval contains 0 
$VAR1 = bless( [
                 50501948,
                 -1,
                 []
               ], 'Item' );
$VAR1 = [];
Can't call method "type" on unblessed reference at ./Caa.pl line 173.
</snip>
[download]

$#retval gives the index of the last element in the array. If an array is empty this will be -1. If it is zero then the array contains one element. Here is a demo:

my @retval;
print "the last index of \@retval is $#retval\n";
print "the number of *elements* in \@retval is ", scalar @retval, "\n"
+;
push @retval, 'one value';
print "the last index of \@retval is $#retval\n";
print "the number of *elements* in \@retval is ", scalar @retval, "\n"
+;
push @retval, 'another value';
print "the last index of \@retval is $#retval\n";
print "the number of *elements* in \@retval is ", scalar @retval, "\n"
+;
[download]

I fully understand the shorthand BTW ;-) The longhand is for your debugging benefit as your code craps out after this as you demonstrate! Also as noted you do not show the method where the error actually occurs. While using OO perl is a great idea your data structures are poor and do not take full advantage of the usual anonymous hash structure. Here is a very brief demo of how I might approach the problem:

package Item;
use Data::Dumper;
my @items;

# initialise an array of item objects from our data
while (<DATA>) {
    chomp;
    next unless $_;
    my $item = new Item;
    my ($id, $quant ) = split ',';
    $item->id($id);
    $item->quant($quant);
    push @items, $item;
}

print Dumper \@items;

# now sell one of each item
for my $item (@items) {
    $item->quant(-1);
}

print Dumper \@items;

# now print out the id and quantities
print "\n\nid      quant\n";
for my $item (@items) {
    print $item->id, "\t", $item->quant, "\n";
}

##############################

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

# get or set id
sub id { 
    my ($self, $cid) = @_;
    $self->{'id'} = $cid if defined $cid;
  return $self->{'id'};
}

# get or set numbers in stock
sub quant {
    my ($self, $change) = @_;
    $self->{'quant'} += $change if defined $change;
  return $self->{'quant'}
}

__DATA__
item 1,10
item 2,20
item 3,30
[download]

cheers

tachyon

s&&rsenoyhcatreve&&&s&n.+t&"$'$`$\"$\&"&ee&&y&srve&&d&&print