Iterating through an array of Class::Struct objects - perl

Question

I'm using the Class::Struct module
and have two structures, Cat and Kitten, Cat is a mother cat, and one of the attributes of Cat should be an array of Kitten objects. I'm having difficulty getting this right.
If I save the kittens array as an object I cannot iterate through it as expected; I just get an array with one element which appears to be an array. If I save it as a reference I can not figure out how to deference it correctly.
#!/usr/bin/perl
use strict;
use warnings;
use Class::Struct;
use Data::Dumper;
struct Cat => [
name => '$',
age => '$',
kittens => '$',
];
struct Kitten => [
name => '$',
age => '$',
];
my $lil_kitten = Kitten->new( name => 'Lil Socks', age => 2 );
my $big_kitten = Kitten->new( name => 'Big Socks', age => 3 );
my $old_kitten = Kitten->new( name => 'Old Socks', age => 4 );
my #kitten_array = ( $lil_kitten, $big_kitten, $old_kitten );
my $kitten_count = scalar #kitten_array;
print "There were $kitten_count kittens\n";
foreach my $k ( #kitten_array ) {
bless $k, 'Kitten';
print "Kitten: ", $k->name, " is ", $k->age, " years old.\n";
print Dumper($k), "\n";
}
my $cat = Cat->new( name => 'Socks' );
$cat->age(17);
#$cat->kittens(#kitten_array);
$cat->kittens(\#kitten_array);
my $ref_type = $cat->kittens;
print "Ref type: ", $ref_type, "\n\n\n\n";
#$kitten_count = scalar #$cat->kittens;
#print "There were $kitten_count kittens\n";
print "Once a cat called ", $cat->name, " who was ", $cat->age, "\n";
#foreach my $kat(#$cat->kittens) {
foreach my $kat($cat->kittens) {
bless $kat, 'Kitten';
print "Kitten: ", $kat->name, " is ", $kat->age, " years old.\n";
print Dumper($kat), "\n";
}

Answer 1

You should initialize 'kittens' to be an array (using '#') and use curly brackets for precedence in the dereference. I have flagged the changed lines with the comment # CHANGED.
#!/usr/bin/perl
use strict;
use warnings;
use Class::Struct;
use Data::Dumper;
struct Cat =>
[
name => '$',
age => '$',
kittens => '#', # CHANGED
];
struct Kitten =>
[
name => '$',
age => '$',
];
my $lil_kitten = Kitten->new( name => 'Lil Socks', age=> 2);
my $big_kitten = Kitten->new( name => 'Big Socks', age=> 3);
my $old_kitten = Kitten->new( name => 'Old Socks', age=> 4);
my #kitten_array = ($lil_kitten, $big_kitten, $old_kitten);
my $kitten_count = scalar #kitten_array;
print "There were $kitten_count kittens\n";
foreach my $k(#kitten_array) {
bless $k, 'Kitten';
print "Kitten: ", $k->name, " is ", $k->age, " years old.\n";
print Dumper($k), "\n";
}
my $cat = Cat->new( name => 'Socks');
$cat->age(17);
#$cat->kittens(#kitten_array);
$cat->kittens(\#kitten_array);
my $ref_type = $cat->kittens;
print "Ref type: ", $ref_type, "\n\n\n\n";
$kitten_count = scalar #{$cat->kittens}; # CHANGED
print "There were $kitten_count kittens\n";
print "Once a cat called ", $cat->name, " who was ", $cat->age, "\n";
#foreach my $kat(#$cat->kittens) {
foreach my $kat($cat->kittens) {
bless $kat, 'Kitten';
print "Kitten: ", $kat->name, " is ", $kat->age, " years old.\n";
print Dumper($kat), "\n";
}
The problem with #$cat->kittens is that it first dereferences $cat to become an array, then tries to call the method kittens() on that array. This involves Perl trying to interpret #$cat as a class name by turning it into a string - that is, scalar #$cat, which is the size of the array. You end up calling "3"->kittens().