perlquestion mbethke <p>I've just extended my [Net::CIDR::Lookup] module with an IPv6 version and am seeing a lot of <a href="http://www.cpantesters.org/cpan/report/d078b122-db1a-11e1-9066-3d54fb7543f5">failed tests form CPANtesters</a>. Clearly an oversight: I just assumed [Socket] would nowadays always export <code>unpack_sockaddr_in6</code> and the like. This needs fixing but there's two things I'm not clear about:</p> <ol> <li>Is there a halfway easy way nowadays to find the oldest version of a module that supports a certain feature in the first place? Searching around here I found a half-decade-old thread that mentions it's a tedious process, but I knew that already :) Basically bisecting one's way through every version on BackPAN should be rather straightforward, maybe someone has written some code for it already?</li> <li>Now I think the IPv6-Socket problem may even be a bit more complicated as e.g. <code>unpack_sockaddr_in6</code> will only actually be functional if the system had IPv6 support at XS compile time, otherwise it's there but croaks when called. I'm quite sure [mod://ExtUtils::MakeMaker] has no way of checking a prerequisite for anything else but a version number, but maybe something like [mod://Module::Build] does? I haven't found anything like it in the docs but I suppose something like this would make sense---a sub instead of a version that just returns a boolean indicating whether the installed version is acceptable: <code> PREREQ_PM => { 'Bit::Vector' => 0, Socket => sub { eval { Socket::unpack_sockaddr_in6("\xa".("\0"x22)."\x01\0\0\0\0"); 1; } or do { $@ and return 0; } } }, </code></li> </ol>