The Room Do I dare disturb the universe?

Version Numbers And Deprecation Policies

Version Numbers and Deprecation Policies

A few days mst pointed out to me the Mojo release notes. I don’t pay attention to the project since these days I have my plate full with Moose, Catalyst, and KiokuDB as well as starting a small business to be paying attention to yet another wheel.

My comment was “wow”. To quote the release notes

0.991250 2009-08-18 00:00:00
    - This release contains many substantial changes that are not
      backwards compatible, but good news is that it's also the last
      major feature breaking release before 1.0. ;)
      Older releases of Mojo did contain additional Mojo::Script::* and
      Mojolicious::Script::* modules that are obsolete now and might
      break this version if they are still present on your system.
      Because of this we highly suggest that you
      DELETE ALL MODULES IN THE "Mojo", "MojoX" AND "Mojolicious"

I was shocked that the deprecation policy of a framework that is being touted so widely as attractive to non perl people would involve the phrase “DELETE ALL MODULES”. I’ve been a Perl developer for over a decade now and I’m not comfortable with having to hunt through my file system and delete files manually. I can only imagine what someone with less experience dealing with Perl’s … evolved … filesystem would think (The phrase “WTF?!?” comes to mind).

But that said, I happily went on about my business because what Mojo does has no bearing on my life since I don’t use it. Today’s feed pulls up Sebastian’s reply to mst’s blog post about deprecations in which is take away was that mst doesn’t understand version numbers. I think someone is missing the point.

As soon as something hits CPAN it is considered stable, good versioning practices are simply thrown overboard. It is pretty much industry standard to use "0." versions for code that you want to release for early user feedback but thats still in development.

This may be true, but the very page he links to there doesn’t say anything about industry standards. In fact it documents in some 4,200+ words that there is no “standard” for versioning. It also says that some projects “use the major version number to indicate incompatible releases”. Which arguably is also an industry standard.

The fact is the only thing you can safely rely upon a version to tell you is that this release is different from that release by at least one line. The line that sets the version number. This is why projects need explicit deprecations policies, which is the real point of mst’s post. One that zby managed to pick up.

zby picks up from Sebastian’s line

Should a project have deprecation policies as soon as it hits CPAN with a development release?

and says

I think the answer should be yes - there should always be a deprecation policy. But this deprecation policy does not need to be the full monty of always keeping the backcompat to at least one major version, using strict deprecation cycles etc - it just needs to be stated explicitely and not relying on the version numbering convention as they are not really universal.

I think that in truth every module (and project) has a deprecation policy … they’re just usually implicit. Users have expectations. They expect that packages touted as making their life easier will in fact make their life easier. They expect code to be stable and to not blithely cause them unnecessary pain. They also expect growth and that old features that they personally don’t use will not get in the way of the future because that causes pain too.

This means that unless you write down explicitly what you plan you not only have an implicit deprecation policy, you have one for every single person that uses your code and has different expectations on how the future releases will affect them. It also means that if you make seemingly random breakages that require manual deletion of file, or even just break your API in way that causes pain without some warning you’re gonna get called on it.

People are not perfect. Communication really is the only solution. In the absence of documented authoritative communication users will form their own opinions.

UPDATE: Apparently TextMate’s Markdown syntax and MovableType’s are not remotely similar. I have fixed the formatting since Sebastian tweeted about this so now I’m sure people are actually gonna read it.