inheritance problems

michaelg has asked for the wisdom of the Perl Monks concerning the following question:

Hi monks
I'm trying to write code of Obj inheritance but I face some problems:

my $jhon = Worker->new_worker();
$jhon->print_worker_data();

my $telma = Worker->new_worker(name   => "Telama",
                   age => 25);
$telma->print_worker_data();

        
my $bob = Manager->new_worker(name   => "Bob",
                   age => 40);
$bob->print_worker_data();
$bob->wc();

##=====================================
package Worker;
sub new_worker { ## Constructor.
    my $invocant = shift;
    my $class = ref($invocant);
    my $self = {
    name   => "Jhon Do",
    age    => 32,
    @_ ,
    }; 
    bless ($self)  ;
    return $self ;
};

sub print_worker_data {
    my $self = shift;
    print $self->{name} . " age is:". $self->{age}."\n";
};
##===========================================


package Manager;

use base ("Worker");

sub wc{
    my $self = shift;
    print $self->{name} . " is in title to use the managers toilet\n";
+ 
};
[download]

OK, I started the Manager pack with "our @ISA = "Worker" but I couldn't do any thing for Bob there, When I wrote "use base ("Worker")" I was able to initiate Bob but I could't activate the wc method. So Bob need to go out with the common people. Thanks guys
Michael

Comment on inheritance problems Download Code

Replies are listed 'Best First'.
Re: inheritance problems by Corion (Patriarch) on Aug 16, 2004 at 12:44 UTC
You are using the single-argument form of `bless`, which does not bless `$bob` into the class `Manager`: `my $bob = Manager->new_worker(name => "Bob", age => 40); print $bob,"\n"; # Worker=HASH(0x15debec)` [download] To properly enable inheritance, you must also properly bless every object into the right class. I don't know where you copied your constructor from, but you shouldn't throw away the package name to use (you put it into `$invocant`), but pass it to `bless` as the second argument: `sub new_worker { ## Constructor. my $invocant = shift; # my $class = ref($invocant); my $self = { name => "Jhon Do", age => 32, @_ , }; bless $self, $invocant; return $self; };` [download] Also, you should consider renaming your `new_worker` method to `new`, as is customary with constructors.	[reply] [d/l] [select]
Re: inheritance problems by dragonchild (Archbishop) on Aug 16, 2004 at 12:46 UTC
Your immediate problem is that you're using the one-argument form of bless. You need to use the two-argument form to get inheritance working. (The second argument defaults to the package the constructor is in.) Your real problem is that you are confused about what's going on in a Perl constructor. I would have written your constructor like so: `sub new_worker { my $class = shift; die "Use the copy constructor!\n" if ref $class; my $self = { name => "John Doe", age => 32, @_ , }; return bless $self, $class; }` [download] You don't need any ref() crud in your constructor. That is cargo-cult programming and merlyn has posted enough diatribes about it, as have many other monks. If you want a copy-constructor, then create a clone() method. (You'll notice I don't allow this method to be a copy-constructor.) ------ We are the carpenters and bricklayers of the Information Age. Then there are Damian modules.... sigh* ... that's not about being less-lazy -- that's about being on some really good drugs -- you know, there is no spoon.* - flyingmoose I shouldn't have to say this, but any code, unless otherwise stated, is untested	[reply] [d/l]
Re: inheritance problems by Joost (Canon) on Aug 16, 2004 at 12:45 UTC
ccn's solution will work, but in the long run, it's probably a better idea to put the Worker and Manager packages in their own module files (Worker.pm and Manager.pm) and `use Worker;` and `use Manager;`. That will make sure all setup code is run before any calls to those packages are made. (The problem with your code is that Manager->new_worker() is called before @Manager::ISA is set) Joost. update: and use `bless {}, $classname;` "What should it profit a man, if he should win a flame war, yet lose his cool?"	[reply] [d/l] [select]
Re: inheritance problems by ccn (Vicar) on Aug 16, 2004 at 12:39 UTC
Try out to enclose your @ISA setup in `BEGIN{}` block	[reply] [d/l]


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