This is a much better Perl OO primer than the one I previously linked: https://www.perl.com/article/25/2013/5/20/Old-School-Object-Oriented-Perl/ . (I am glad to see that it sends parameters to functions as a hashtable by reference instead of by value).

But I forgot to mention one important detail. Huge really. If the inherited (child) class has its own constructor (overriding - or more brutally, overwriting - the parent's constructor) then you must call in it the parent's constructor yourself before you do any more initialisation. Like so:

package Child;
use parent 'Parent';
sub new {
    my ($class, $params) = @_;

    # call parent's constructor first with the given parameters
    # the parent should ideally filter out the parameters
    # that do not concern it and ignore them rather than complaining a
+bout illegal params
    my $self = $class->SUPER::new($params);
    # at this point $self has all Parent's initialisation
    # (whatever was done and set in its constructor).

    # Now do local initialisation on $self which is Parent's self (a {
+} in most cases)
    ...
    $self->{child_extra_property_1} = 12; # for example
    ...

    # and bless to Child - actually that's a re-bless because calling
    # Parent's constructor blessed $self to be an object of class 'Par
+ent'
    # so now make it of class 'Child'
    bless $self => $class;
    return $self;
}

[download]

bw, bliako

In reply to Re^4: Mass Class Confusion - Who calls what how? by bliako
in thread Mass Class Confusion - Who calls what how? by holandes777

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