in reply to (Ovid) Re: is there a way to check @ISA from upstream?
in thread is there a way to check @ISA from upstream?

heh. for some definitions of "poorly".

Problem:
Trying to allow lazy maintenance of multiple interface widgets, frinstance Receipt::DoubleA, Receipt::TextOnly, Receipt::BannerAds, etc

at a level above the widgets, we have an AUTOLOAD that allows us to call $ui->Receipt->build(%args), and it will use the Receipt parent class or choose the right subclass based on external criteria.

The problem is, for example, that we might have a Text subclass under Receipt, but not have one under Error.

In that case we could

  • 1) mandate the creation of an "empty" subclass for every widget for each new interface, with at minimum an @ISA statement
  • 2) descend into some inelegant evalling or -e testing at some level (perhaps in the parent widget class), or
  • 3) see if there might be a way to check from upstream if in fact there was a Text interface for a particular widget before trying to AUTOLOAD it.
  • 4) accept new and novel suggestions from perlmonks, et al.

    Ideally, without keeping a separate registry hash of available interfaces, of course ;)

    As you noted, perhaps too tricky. The extenuating circumstances of how we got here are lengthy and boring.

    {::} =D------an (sometimes the cord just doesn't quite reach)

    • Comment on (dan2bit) Re: (Ovid) Re: is there a way to check @ISA from upstream?

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    Re: (dan2bit) Re: (Ovid) Re: is there a way to check @ISA from upstream?
    by merlyn (Sage) on May 10, 2001 at 00:10 UTC
      Would UNIVERSAL::can help here at all? And perhaps understanding that when you define AUTOLOAD, you should also override can?

      -- Randal L. Schwartz, Perl hacker

    		[reply]
        alas. it would appear that UNIVERSAL::isa and UNIVERSAL::can will not be much help in detecting classes which do not appear in use statements

        use Receipt::TextOnly;
print '#output: '.UNIVERSAL::isa('Receipt::TextOnly','Receipt')."\n";
print '#output: '.UNIVERSAL::can('Receipt::TextOnly','render')."\n";
#output: 1
#output: CODE(0x84baf38)

        [download]

        but 

        use Receipt;
print '#output: '.UNIVERSAL::isa('Receipt::TextOnly','Receipt')."\n";
print '#output: '.UNIVERSAL::can('Receipt::TextOnly','render')."\n";
#output:
#output:

        [download]
        the second code snippet outputs undef. Back to options 1 or 2.

        {::} =D------an (sometimes the cord just doesn't quite reach)

    		[reply]
    [d/l]
    [select]
          I don't know what you mean "do not appear in use statements", so I cannot understand the point you are making.

          Show me the code in Receipt::TextOnly and Receipt, and perhaps I can help add useful behavior here.

          -- Randal L. Schwartz, Perl hacker

    		[reply]

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