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

Greetings,

I'm looking for a cleaner way to test if a package member exists/is valid.

I'm currently testing it thusly: 
package Util::Stuff::abc;
sub attrib1 { 1  }
sub attrib2 { 10 }
...

eval { $symref->attrib1; };

if (!$@) {
   ... $symref->attrib1 is OK ...
}

[download]
Is there a cleaner way?

Regards
Henry

UPDATE: forgive me if I'm not using the correct Perl nomenclature. I'm an old procedural boy an' all this OO'ism makes me sleepy...

Replies are listed 'Best First'.
Re: Testing package membership
by GrandFather (Saint) on Nov 21, 2008 at 08:45 UTC

    If you are testing for methods you can:

    use strict;
use warnings;
use strict;

package Abc;

sub new {
    return bless {}, shift;
}

sub attrib1 { 1  }
sub attrib2 { 10 }


package main;

my $abc = Abc->new ();

for my $methName (qw(attrib1 attrib2 attrib3)) {
    next unless my $meth = $abc->can ($methName);
    print "Can $methName: ", $meth-> (), "\n";
}

    [download]

    Prints:

    Can attrib1: 1
Can attrib2: 10

    [download]
    Perl reduces RSI - it saves typing
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[d/l]
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      Thanks - but I need to step through almost a hundred packages (which is existing code) extracting those attribute values. So modifying the code and adding sub new() for each is problematic.
[reply]

        There is a theme running through your last three questions, but it's not clear to me just what you are trying to achieve (although you could be trying to auto-document some legacy code). We may be able to help more if you let us in on the bigger problem.

        Perl reduces RSI - it saves typing
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Re: Testing package membership
by moritz (Cardinal) on Nov 21, 2008 at 08:46 UTC
    You can ask with $ref->can('methodname') or yourpackage->can('methodname') if such a method exists (which will not work if AUTOLOAD is in effect, but otherwise it's fine).

    can is defined and documented in UNIVERSAL.

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[d/l]
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      Got it! Using ->can() wrapped in eval{} does the trick nicely: 
      package Util::Stuff::abc;
sub attrib1 { 1  }
sub attrib2 { 10 }
...

eval {
if ($symref->can('attrib1')) {
   ... $symref->attrib1 is OK ...
}};

      [download]
      Thanks to GrandFather and moritz.
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[d/l]
[select]
      Hmm, looks like AUTOLOAD is in effect since ->can() is failing.

      Looks like I'm stuck with eval{}, unless there's another way.

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