The Room Do I dare disturb the universe?

The Stability Of Abstract Layers

The Stability of Abstract Layers

One of the reasons that Moose really works is that it’s a layer of abstractions. At the bottom you have Perl’s native OO layer which is … let’s be charitable and say “bare bones”. On top of that Stevan wrote Class::MOP which standardizes the lower layer, cleans up the edge cases, implements some best practices, and gives you a massive level of introspection over everything. On top of Class::MOP is Moose which brings in a new layer of features including Roles, Delegation, Type Constraints and the other goodies you’ve heard so much about. On top of Moose are things like MooseX::Declare and the rest of the MooseX:: namespace that can extend the features that Moose provides in new directions.

This stack works precisely because it is a stack. Nested layers of abstraction means you have a consistent base and you can play TIMTOADY on top of it as much as you like but you get the consistency of a stable API at the center. Eventually the new layers on top become a base for layers atop them. The current discussion about the Perl release system seems to me to really be about this idea. chromatic pointed out that Rakudo has had more stable releases than Perl5 in the time since the Perl6 announcement was made. This is true, but Rakudo’s idea of stable is smaller stack of abstractions than Perl5’s. Rakudo doesn’t ship 114 external modules. It doesn’t even ship 100% of the spec’d Perl6 features. Claiming that Rakudo’s concept of stable is comparable to Perl5’s is disingenuous. I’m sure chromatic was trying to highlight this discussion on what stability is rather than trying to troll with statements full of FUD, he’d be the first to defend Perl if someone else were to make this statement.

The right answer is probably a middle ground. Lots of people agree that Perl should ship a smaller Core set of modules, perhaps a smaller set of core features would help too, something to enable more externalizing of hooks like Devel::Declare. I’m already failing at my volunteer effort to drive the first part, I doubt I’d be the right person for the second (but I’m willing to try).

This same idea comes up as well with the comparison of stability between Module::Build and Module::Install. Those on the Module::Build side point out that having a single API means that everybody is on the same page and that you can trust all installers are equal. The Module::Install people tend to point out that not all distributions are equal and that having everybody conform to the same API causes problems when you try upgrading that API (not everything is installed equally everywhere).

It seems to me that the answer is to have a core API (Module::Build, EUMM it doesn’t matter), and a stack of abstractions on top of that where you can do experimental extensions. Module::Install currently does this on top of EUMM.