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Re: Re: Griping about Typing

by pdcawley (Hermit)
on Apr 19, 2002 at 07:04 UTC ( #160451=note: print w/ replies, xml ) Need Help??


in reply to Re: Griping about Typing
in thread Griping about Typing

You can already document your intent

my $bork = Bork->new(); my Chef $x = $bork->bork->bork;
Only trouble is (gee whizz!) I'm dreaming my life away.

Ahem, back at the plot, the trouble is that perl will silently ignore your careful predeclaration and assign to $x even if ! $bork->bork->bork->isa('Chef'), which is a shame. use strict 'declarations' anyone? Implementation left as an exercise to the interested reader obviously. Me and C don't get on.


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Re^3: Griping about Typing
by tadman (Prior) on Apr 19, 2002 at 18:51 UTC
    Okay, can anyone explain how that works? It actually parses, though the class is completely ignored, provided it is defined somewhere. Here's a quick example:
    #!/usr/bin/perl -w use strict; use CGI; use LWP; my CGI $cgi = new CGI(); # Works my XYZ $cgi = new CGI(); # "No such class XYZ ..." my LWP $cgi = new CGI(); # Works, strangely enough
    Nothing in the docs about that, at least under my.
      It isn't quite ignored, but it only really does anything if you're using pseudo hashes and you've defined your the class using use fields, in which case, $CGI would be initialized as an arrayref with an appropriate hashref in the zeroth slot.
      Perl records this information, but does nothing (or very little) with it. Because it is recorded, the typesafety.pm and types.pm modules are able to use it. This kind of core hooks for extensibility via modules is a recurring pattern in Perl: overload.pm can intercept the definitions of constants and turn them into objects; attributes.pm handles cases where tags like :foo appear after variables or sub definitions (in cases where the tag isn't one of the built ins like :lvalue, :method, or the depricated :shared). This feature, like attributes, went through growing pains. It is undocumented because it is still experimental - the details of how and when it is used are up in the air, even though some experimental modules are using it now.

      The short of it is, use types.pm and/or typesafety.pm. http://perldesignpatterns.com/?TypeSafety has an intro to the idea of type safety and details about the Perl implementations. It quotes this thread heavily =) I hope this answers your question.

      -scott

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