Question

I have some problems calling a constructor with a hash.
I get the error:

“Odd number of elements in hash assignment at Sumcheck.pm line 4”.
Sumcheck.pm looks like this:

package Sumcheck;

sub new {
    my ($debug, $debug_matches,%checkHash) = @_;
    my $self = {};
    $self->{DEBUG} = $debug;
    $self->{DEBUG_MATCHES} = $debug_matches;
    $self->{CHECKRESULT_OK} = "COMPLIANT"; 
    $self->{CHECKRESULT_ERROR} = "NONCOMPLIANT"; 
    $self->{checkHash} = %checkHash;
    #print %checkHash;

    bless($self);
    return $self;
}
1;

And i call it like this(just a random hash):

use Sumcheck;
$debug = 0;
$debug_matches = 1;

%checkHash = (  'The Shining'       => 'Kubrick',
                'Ten Commandments'  => 'DeMille',
                'Goonies'           => 'Donner',);

$sumCheck = Sumcheck->new($debug, $debug_matches, %checkHash);

Why do i get this error? How it is solved?

Thx 🙂

Answer 1

The first implicit argument to a method called like this:

MyPackage->someMethod()

is the name of the package. Eg:

package MyPackage;

sub someMethod {
    print shift;

will yield MyPackage.

The idea WRT to constructors is:

sub new {
    my $class = shift;  # now your $debug would be $_[0], so:
    my $self = { @_ };  # <- replace this with your own details
    bless $self, $class;
}

You don’t have to do exactly that, but do you see now why your hash has an odd number of elements? In Sumcheck::new, $debug is not what you think it is (check). Remember, a hash is passed literally as a list like this:

name, value, name, value

So, “Sumcheck” (the package name) gets placed in $debug, 0 gets placed into $debug_matches then the first element of the hash is 1, leading to this:

1 => `The Shining`
'Kubrick' => 'Ten Commandments',
'DeMille' => 'Goonies',
'Donner'  =>  # uneven number of elements error

FYI, the first implicit argument to an object method called this way (the second line):

my $obj = Sumcheck->new(..,.);
$obj->someMethod();

Will be $obj, aka. the $self in the method:

sub someMethod {
    my $self = shift

which is the blessed hash returned by the constructor, new().