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How can I make one class extend another one?

by Anonymous Monk
on Apr 20, 2000 at 20:27 UTC ( #8181=categorized question: print w/replies, xml ) Need Help??
Contributed by Anonymous Monk on Apr 20, 2000 at 20:27 UTC
Q&A  > object-oriented programming


Answer: How can I make one class extend another one?
contributed by chromatic

Inheritance is very easy in Perl. Assuming we have a class PerlMonk, we could create a new class called vroom that extends the first:

package vroom; @ISA = qw ( PerlMonk );
From then on, for any method called on an instance of vroom that isn't defined immediately in the class, Perl will search the classes named in @vroom::ISA for those methods.

That is, PerlMonk::dispense_wisdom() is available via $vroom->dispense_wisdom() even if there is no vroom::dispense_wisdom().

Note that the @ISA array can contain lots of parent classes. Note also that they are searched left-to-right, depth first.

Answer: How can I make one class extend another one?
contributed by brother ab

package Child; use base qw(Mother Father);

base pragma not only includes extended classes in @INC, but 'require's them.

Additionally, it is integrated with fields pragma (if you like strict data members protection)

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    [Corion]: And performance linear to the number of registered one-shots doesn't feel that bad. Maybe I should collect statistics on how many callbacks are outstanding ;)
    [Corion]: choroba: Yes, but the longer I thought about efficient hashes mapping the event type back to their callbacks, and how to keep them in sync, the more I thought that all that optimization might just not be worth it, even if it's horribly inelegant
    [Lady_Aleena]: My biggest problem with hashes at the moment is one with 2,501 keys.
    [choroba]: how many event types are there?
    [Corion]: Also I found that I can't conveniently weaken an array slot, which also is inconvenient, as I want my one-shots to disappear if the caller discards them
    [Corion]: choroba: Currently two or three that my program handles (WWW::Mechanize:: Chrome), but there might be more that become interesting
    [Corion]: But I don't expect more than 100 to be active at the same time, so I'm not really sure if there is a not-too-fancy data structure that is maintained with few lines of code where the performance is better than the linear scan ;)
    [Corion]: But I should do a mock-up program so that others can see what I'm talking about ;)
    [robby_dobby]: Corion: I hope you know all too well that passing around "fancy" datastructures is a recipe for disaster :-)
    [robby_dobby]: As in, it's-too-fancy- that-it-will-be- messy-to-handle

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