ap.pm:
package ap;

sub new {
    my $self = {};
    bless $self; #comment this will cause the error you described.
    return $self;
}

sub item_id {
    my $self = shift;
    if (@_) {
        $self->{ITEM_ID} = shift;
    } 
    return $self->{ITEM_ID};
}

1;

ap.pl:
use ap;
use strict;

my $a = new ap;
$a->item_id(10);
print $a->item_id();
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A ref becomes an object after being blessed, as now Perl knows who/what it is.

This is incorrect, and will eventually bite you in the rear end. From perlfunc:

       bless REF,CLASSNAME
       bless REF
               This function tells the thingy referenced by
               REF that it is now an object in the CLASSNAME
               package...
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It is the thing referred to, not the reference, that is blessed. This is why we can copy the reference returned by bless and still invoke methods against the reference--perl knows that the reference refers to an object of class class because it's the referent that is marked as belonging to a particular package.

Thank you for making what I said more formal, but to be honest, I mean exactly the same thing, and I didn't expect people to misunderstand it. (Or to be precise, you correctly understood what was on the screen word by word, but had the wrong expectation.)

This is a good lesson, and I will try to make my wording more formal.

Thank you all. Problem eliminated.

Hello, I tried 'use warnings' and 'use diagnostics' and received the same message. Here's part of the code:

sub get_product_table
{
my $sth = shift;
my @row;

              
    
    while (my $ref = $sth->fetchrow_hashref ())
    {
my $serve_url = sprintf ("serve_image.cgi?item_id=%s",
                                escape ($ref->{item_id}));
        

# generate a form allowing a quantity of the item to be added
# to the cart
push (@row, start_form(-method=>'GET', -action=>url()),
hidden( -name => "choice", -override => 1, 
-default => "add" ),
hidden( -name => "item_id", -override => 1, 
-default => escapeHTML( $ref->{item_id} )),
        Tr (
   print img ({-src => "$serve_url;thumbnail=1", -alt => $ref->item_id
+}), 
   td ( escapeHTML( $ref->{item_id} )),
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I believe the line that is causing the problem is the line that starts with "print img". Thanks

And you are correct.
You wrote '$ref->item_id' when you probably meant '$ref->{item_id}', it's trying to call item_id as a function/method..
C.

Update: I believe that

   ...$ref->item_id}...
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  ...$ref->{item_id}...
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