oo perl - using the super-class

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

ok, i have a class called transaction which i initialise with a request string. my application will soon support more than one type of transaction, so what i'd like to do is keep this in the code:

$work = new Transaction($request)
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but have the Transaction class return a sub class of Transaction. let's say TransactionA or TransactionB. now i assume i would do something like:

sub new {
    my($r) = @_;

    if (&test($r)) {
    return new TransactionA($r);
    } else {
    return new TransactionB($r);
    }
}
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although i suppose Transaction isn't really a superclass anymore. anyway i guess my question really boils down to, "what is a clean way of creating an object of differing types based on data passed to a constructor?"

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Re (tilly) 1: oo perl - using the super-class by tilly (Archbishop) on Oct 03, 2000 at 15:07 UTC
Perl has a standard way of doing it already. Create your sub-classes TransactionA and TransactionB, put Transaction in @ISA for each. Have your Transaction constructor respect inheritance by using the two-argument form of bless. For instance: `sub new { my $class = shift; my $self = {}; %$self = @_; # Whatever fits - this is just and example return bless($self, $class); }` [download] And now your end code will be able to say: `my $trans = new TransactionA;` [download] and it will all work. For more take a look at this tutorial.	[reply] [d/l] [select]
RE: Re (tilly) 1: oo perl - using the super-class by kevinlyda (Initiate) on Oct 03, 2000 at 18:50 UTC
hm, no, that's exactly what i don't want. i never want to have the main code say: `$trans = new TransactionA` [download] i want to say `$trans = new Transaction($request);` [download] and have $trans be an instance of TransactionA or TransactionB. i'm not up on oo terminology, but i think what i really want is a TransactionFactory class. again, i'm not sure but the above describes what i'm looking for. i'm just wondering if it's a good thing to look for or is there a better design to use?	[reply] [d/l] [select]
RE: RE: Re (tilly) 1: oo perl - using the super-class by merlyn (Sage) on Oct 03, 2000 at 18:52 UTC
Your original code was fine. Just make sure that neither of your two specific types of transaction inherit from the generic transaction, or you're toast on the `new` routine! -- Randal L. Schwartz, Perl hacker	[reply]
RE (tilly) 3: oo perl - using the super-class by tilly (Archbishop) on Oct 03, 2000 at 18:53 UTC
Well you can do whatever you want with the two argument form of bless, but you will break inheritance. OTOH containment (ie making one property of an object be a member of a different class) is usually cleaner than inheritance anyways, but if you play this kind of game you really should document it to avoid potential grief for someone else.	[reply]