You can use Class::MOP or it's offspring Moose to do this.

First the Class::MOP version ...

package TestPackage;
use metaclass; # this sets up your class to use Class::MOP
use Data::Dump qw( dump );

my $obj = bless {}, __PACKAGE__;

print 'Can dump()' if $obj->meta->has_method('dump');
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This will not print "Can dump()" since Class::MOP knows that the method is not actually from your package, but has been imported from another package. To find the "interface" with Class::MOP, you have a few choices. First you can get all the locally defined methods* like this:

my @methods = $obj->meta->get_method_list;
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This will return a list of method names suitable for doing things like $obj->meta->has_method($method_name) and $obj->meta->get_method($method_name) and other such introspection and reflection. Or, your second choice is to get all the methods this $obj supports, including inherited methods. In this case you do the following:

my @methods = $obj->meta->compute_all_applicable_methods;
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The items in @methods this time are slightly different, you get a HASH reference which contains the method name (in the name key), the name of the class in which the method lives (in the class key) and a CODE reference for the actual method (in the code key).

Now, you could also use Moose and Moose::Role to do similar things. Moose is basically syntactic sugar over the mechanisms that Class::MOP provides, so all the above examples apply here as well. With roles** and Moose::Role you can do the interface checking you are talking about. Here is an example:

package MyFooInterface;
use Moose::Role;
requires 'bar';
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Then you apply the role to your class, which checks the role "interface" at compile time.

package MyFoo;
use Moose;
with 'MyFooInterface';
sub bar { ... } 
# the bar method is required, the 
# class will fail to compile if it is 
# not present
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And you can also do your checking at runtime ...

my $foo = MyFoo->new;
if ($foo->does('MyFooInterface')) { ... }
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For more information, see the CPAN pages for Moose or Class::MOP, or for a quicker overview you can check out one of these talks recently given on the subject:

• An excellent Intro to Moose (20 min talk)
• A slightly more involved into to Moose (50 min talk)
• A quick Role talk (20 min)

And lastly, you can check out the two part article on Moose written by our very own merlyn.

Footnotes:
* Locally defined methods are those defined directly in your class, and not inherited.
** If you don't already know, a role is not unlike a mixin or the traits mentioned above, but with a little bit more of a Perl-ish twist. They are a core part of Perl 6 in fact.

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