Lotus1 has asked for the wisdom of the Perl Monks concerning the following question:

This is from the examples section of Net::DNS :

use Net::DNS;
my $res   = Net::DNS::Resolver->new;
my $reply = $res->search("www.example.com", "A");
 
if ($reply) {
    foreach my $rr ($reply->answer) {
        print $rr->address, "\n" if $rr->can("address");
    }
} else {
    warn "query failed: ", $res->errorstring, "\n";
}

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The search method in the resolver returns a packet object. Then the 'answer' method of that (from Net::DNS::Packet) "Returns a list of Net::DNS::RR objects representing the answer section of the packet." I've looked through the documentation for Net::DNS::RR and the module sourch but can't find the description of what the 'can' method is. The example runs without errors while using strict and warnings. Any suggestions?

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Re: In Net::DNS::RR what is the 'can' method? (updated)
by haukex (Archbishop) on Sep 19, 2018 at 18:15 UTC

    It's probably UNIVERSAL::can.

    Update: Yep, looks like it. UNIVERSAL is Perl's implicit base class for all objects. can queries whether the object has that method (including via inheritance). It looks like the Net::DNS docs are suggesting to use duck typing here to tell whether the Net::DNS::RR subclass has the address method. An alternative would be to use isa (also from UNIVERSAL) to see if an object is of a certain class (or is one of its subclasses) and therefore supports that class's methods. The thing about that is though that you'd have to test against a whole list of Net::DNS::RR subclasses. As long as all of the subclasses' address methods behave the same, duck typing is safe here, and easier.

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      Thanks! I didn't know about that one.

      Edit: Other examples I've seen just test if the response object is true since it will be 'undef' if there were no responses.

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