"Can't locate object method "new" [...]" in Perl using the AI::Pathfinding::AStar CPAN module

Question

This is the first "serious" thing I'm doing in Perl, so please pardon me if the question is somewhat silly.

I wanted to play around with the A* pathfinding algorithm. I found the AI::Pathfinding::AStar CPAN Module and am basically trying to get the given example to work.

First of all I separated the example into two files, because I couldn't figure out how to make the use My::Map::Package; work with everything in a single file. I came up with the following two files:

MyAstar.pm:

package MyAstar;
use warnings;
use strict;
use base "AI::Pathfinding::AStar";

my %NODES = get_all_nodes();
sub get_all_nodes {...}
sub getSurrounding {...}

main.pl:

#!/usr/bin/env perl

package main;
use lib '/home/foo/astar/';
use warnings;
use strict;
use MyAstar;

my $map = MyAstar->new or die "No map for you!";
my $path = $map->findPath(1, 5);
print join(', ', @$path), "\n";

When I execute main.pl I get the following error:

Can't locate object method "new" via package "MyAstar" at main.pl line 9.

I'm not sure what the problem is here. I would have expected, there to be a subroutine by the name new in the AI::Pathfinding::AStar package, but couldn't find it. Is the CPAN Module broken or am I doing something wrong?

Answer 1

You try to call a function (MyAstar->new, which conventionally is used as a constructor), but you don't define it. There is no default constructor in Perl (like in e.g., Java).

Add something like this to your MyAstar.pm:

sub new {
    my $class = shift;
    my $self = bless{}, $class;
    # initialize $self here as needed, maybe using any passed arguments in @_
    return $self;
}