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

I have a class that contains a number of 'build_*' methods. It is written to be subclassed, so that it can be easily extended. Most extension would be to create new 'build_' methods.

One routine I have written calls the various 'build_' methods based on XML elements. I would like to test and make sure that the method is available before calling it.

I've tried Module::Info, but this actually parses the given module file looking for methods; if the modules has been subclassed, it won't find the new methods. My other inclination is to simply wrap the method call in an eval statement.

So my question is: Is there an easy way of finding out what methods are available to an object? Or is perl way of doing it to test for exceptions?

  • Comment on Determining what methods are available to a class

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Re: Determining what methods are available to a class
by The Mad Hatter (Priest) on Aug 09, 2003 at 14:30 UTC
    Use the can method (provided by the UNIVERSAL base class)... 
    my $method = "build_a_kite";
if ($obj->can($method)) {
    print "We can!";
}
else {
    print "We can't...";
}

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    From perldoc UNIVERSAL... 
    $obj->can( METHOD ), CLASS->can( METHOD ), can( VAL, METHOD )

can checks if the object or class has a method called METHOD. If
it does then a reference to the sub is returned. If it does not
then undef is returned. This includes methods inherited or
imported by $obj, CLASS, or VAL.

can cannot know whether an object will be able to provide a method
through AUTOLOAD, so a return value of undef does not necessarily
mean the object will not be able to handle the method call. To get
around this some module authors use a forward declaration (see
perlsub) for methods they will handle via AUTOLOAD. For such
'dummy' subs, can will still return a code reference, which, when
called, will fall through to the AUTOLOAD. If no suitable AUTOLOAD
is provided, calling the coderef will cause an error.

can can be called as a class (static) method, an object method, or
a function.

When used as a function, if VAL is a blessed reference or package
name which has a method called METHOD, can returns a reference to
the subroutine. If VAL is not a blessed reference, or if it does
not have a method METHOD, undef is returned.

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[d/l]
[select]
      Thanks -- that's exactly what I was looking for. Need to read that perldoc a little more closely now!
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Re: Determining what methods are available to a class
by larsen (Parson) on Aug 09, 2003 at 14:50 UTC
    Another way is to look into the package symbol table. For example: 
    use strict;
use warnings;

use Devel::Symdump;

use CGI; # for our example we will look into the CGI package

my $obj = Devel::Symdump->rnew( 'CGI' );

my @f = $obj->functions;

print join "\n", @f;

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    And here part of the output: 
    CGI::Util::rearrange
CGI::Util::make_attributes
CGI::Util::utf8_chr
CGI::Util::simple_escape
CGI::Util::unescape
...
CGI::croak
CGI::import
CGI::binmode
CGI::self_or_CGI
CGI::expires
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[d/l]

      Unfortunately, that doesn't account for inherited methods or AUTOLOADed methods. (Remember to write your own can() when you AUTOLOAD() accessors and such.)

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Re: Determining what methods are available to a class (-d/m)
by tye (Sage) on Aug 09, 2003 at 22:54 UTC 
    > perl -de 0
  DB<1> h m
m expr          Evals expression in array context, prints methods
                callable on the first element of the result.
m class         Prints methods callable via the given class.

  DB<2>

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    So something like: 

    > perl -MMy::Module -de 0
  DB<1> m My::Module

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                    - tye
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Re: Determining what methods are available to a class
by adamk (Chaplain) on Aug 10, 2003 at 02:24 UTC
    Class::Inspector
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