Implementing Tree in Perl - Children cut off - perl

Question

I'm to learn Perl for a job interview over weekend. In order to get a deeper understanding I'm trying to implement a tree class.
#use strict;
#use warnings;
package Tree;
sub new {
my $class = shift #_;
my $content = shift #_;
my #array = shift #_;
return bless { "content" => $content, "array" => #array }, $class;
}
sub num_children {
my $self = shift #_;
my #array = $self->{"array"};
return scalar #array;
}
return 1;
To test the (faulty) tree class I have implemented the following test script.
#!/usr/bin/perl
require Tree;
my $t = Tree->new("#", undef);
my $tt = Tree->new("*", undef);
my $tttt = Tree->new("-", undef);
my $ttttt = Tree->new(".", undef);
my #list = ();
push #list, $tt;
push #list, $t;
push #list, $tttt;
push #list, $ttttt;
my $ttt = Tree->new("+", #list);
print $ttt->num_children();
Unfortunately the output is 1 instead of my expection of 4. I assume the array is somehow cut off or unvoluntarily converted to a scalar. Any Ideas?

Answer 1

The main problem is that you can't pass arrays as a single value—you have to pass a reference instead.
Also, you should never comment out use strict and use warnings. They are valuable debugging tools, and if you are getting error messages with them enabled you should fix the errors that they are flagging instead.
Here's a working Tree.pm
use strict;
use warnings;
package Tree;
sub new {
my $class = shift;
my ($content, $array) = #_;
return bless { content => $content, array => $array }, $class;
}
sub num_children {
my $self = shift;
my $array = $self->{array};
return scalar #$array;
}
1;
and the calling program tree_test.pl. Note that you should use rather than require a module.
#!/usr/bin/perl
use strict;
use warnings;
use Tree;
my #list = map { Tree->new($_) } ('#', '*', '-', '.');
my $ttt = Tree->new('+', \#list);
print $ttt->num_children, "\n";
output
4

Answer 2

shift only removes one element from an array. Populate #array without it:
my #array = #_;
But, you can't store an array in a hash directly, you have to use a reference:
return bless { content => $content,
array => \#array,
}, $class;
which you then have to dereference:
my #array = #{ $self->{array} };
return scalar #array