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What CPAN modules are "good reads"?

by tlm (Prior)
on Jun 13, 2005 at 17:52 UTC ( #466234=perlquestion: print w/ replies, xml ) Need Help??
tlm has asked for the wisdom of the Perl Monks concerning the following question:

IMO, the Perl literature is relatively thin on matters of module/class design and organization. A typical response to this observation is to point to CPAN while saying the words "Use the Source, Luke!" Unfortunately, CPAN modules are often quite difficult to read. This may be because the module is badly written, or because it is doing some very cutting edge stuff that only the most advanced Perl programmers can follow. Or perhaps because it is too huge to be comprehensible by the uninitiated.

What CPAN modules stand out in your experience for their readability and "didactic value"?

the lowliest monk

Comment on What CPAN modules are "good reads"?
Re: What CPAN modules are "good reads"?
by ghenry (Vicar) on Jun 13, 2005 at 17:57 UTC

    I have learnt a lot from CGI.pm

    Walking the road to enlightenment... I found a penguin and a camel on the way.....
    Fancy a yourname@perl.me.uk? Just ask!!!
      Better unlearn it fast!

        Yes, it sounds as if I should.

        Walking the road to enlightenment... I found a penguin and a camel on the way.....
        Fancy a yourname@perl.me.uk? Just ask!!!

        Err... why?

      As in, "What not to do?" {grin}

      Let's see:

      • The "lincoln loader" instead of SelfLoader: check
      • Custom importer instead of Exporter: check
      • Funky "is this a method or a subroutine" repeated everywhere: check
      • Funky "args preceded by dash and/or args inside a hashref": check
      • Odd mix of globals and/or use parameters and/or object instance vars to determine behavior: check
      Admittedly, some of this stuff was created before the core functionality was available. But there's some mighty scary code in there.

      In Lincoln's defense, this code is probably the second most frequently invoked module, after strict, and has had to deal with a lot of legacy issues.

      -- Randal L. Schwartz, Perl hacker
      Be sure to read my standard disclaimer if this is a reply.

Re: What CPAN modules are "good reads"?
by dbwiz (Curate) on Jun 13, 2005 at 18:18 UTC

      DBI is great, but it's source can be hard to follow at times unless you are willing to dive into the XS code, and DBI::PurePerl is not a complete DBI implementation and so somewhat hard to follow too.

      However, that said, if you can manage to get your head around DBI you will certainly learn a lot.

      -stvn
Re: What CPAN modules are "good reads"?
by samtregar (Abbot) on Jun 13, 2005 at 18:49 UTC
    I addressed this in chapter 7 of my book - Writing Perl Modules for CPAN. You can download it for free.

    Interestingly, the two modules mentioned above - DBI and CGI - are both on my list of great CPAN modules but I don't consider either to be "good reads" for learning about Perl module design. They both contain rather unusual abuses of Perl's OO system that shouldn't be replicated without due cause.

    -sam

Re: What CPAN modules are "good reads"?
by fauria (Deacon) on Jun 13, 2005 at 19:20 UTC

      I've always liked the idea that a good Acme module not only does something useless, but it also shows off an interesting use of Perl in a fairly clear way.

      Maybe the cleanest Acme module is Acme::Bleach :)

      Flavio (perl -e 'print(scalar(reverse("\nti.xittelop\@oivalf")))')

      Don't fool yourself.
Re: What CPAN modules are "good reads"?
by stvn (Monsignor) on Jun 13, 2005 at 21:31 UTC

    I have found DBD::mysqlPP to be very cleanly written code, and a wonderful way to learn more about DBD's (I use it as reference everytime I get stuck with DBD::Mock).

    I was also reading the Catalyst sources recently and found them very interesting.

    I usually try to read modules that I myself use, because I find it much easier to map my own usages to the source code I am looking at . Lots of "oh, so that's how they did it" moments and the like.

    As for the module/package organization part of your question. I think this is partially a personal style choice, but in general good modular decomposition is good modular decompostion :)

    -stvn
      Catalyst contains some code that I consider pretty questionable -- things like undocumented abuses of import(), assumptions about the internal structure of other people's classes, etc. It's not all bad, but I wouldn't call it "clean."
        Feel free to discuss this on the Mailinglist.

        Isn't blind bashing under your level? This is everything, but not productive...

        undocumented abuses of import()

        The only place we use import() is when you declare which engine and plugins you want to use, but it is documented.

        assumptions about the internal structure of other people's classes

        We only make a assumption of your internal structure if you inherit from Catalyst::Base and don't overload the constructor, perfectly sensible IMO.

        etc

        It would be interesting to hear about the real cases, where we are unclean.

        I'm still waiting for a response to this. I'm all for reasoned debate, but you've made sweeping criticisms of Catalyst, without backing up your claims. No Open Source project is above criticism, but it should be measured and considered. Come on, show us some examples of "undocumented abuses of import(), assumptions about the internal structure of other people's classes." If you can't find any, then the developers don't deserve the slur on the project, and if you can then hopefully they'll work to make it better.
Re: What CPAN modules are "good reads"?
by tilly (Archbishop) on Jun 13, 2005 at 21:41 UTC
    I personally liked LWP as an example of OO design.

    And, of course, anything by TheDamian walks that fine line between inspiration and madness. OK, I lie. Many of them don't walk. They stagger somewhere close, where "close" is measured in very large units. But still they are interesting reads.

Re: What CPAN modules are "good reads"?
by perrin (Chancellor) on Jun 13, 2005 at 22:41 UTC
    Template Toolkit has a nice design and clean code. OpenInteract2 looked pretty good to me too, but I don't know it as well.
Re: What CPAN modules are "good reads"?
by rinceWind (Monsignor) on Jun 13, 2005 at 23:39 UTC

    I'm surprised that nobody has mentioned the Perl Advent Calendar. 2004 was its fifth year.

    --

    Oh Lord, won’t you burn me a Knoppix CD ?
    My friends all rate Windows, I must disagree.
    Your powers of persuasion will set them all free,
    So oh Lord, won’t you burn me a Knoppix CD ?
    (Missquoting Janis Joplin)

Re: What CPAN modules are "good reads"?
by donarb (Beadle) on Jun 14, 2005 at 03:09 UTC
    I don't have a specific CPAN module in mind, but any module which contains a thorough test harness is a great read, because it shows how to use the module and all of its APIs. Sometimes the POD lags behind, but if there is a test for it, the test helps to explain what it does and how to call it.
Re: What CPAN modules are "good reads"?
by SolidState (Scribe) on Jun 14, 2005 at 10:50 UTC

    IO::All stands out in my opinion. It seperates All.pod from All.pm (which I have always felt is the right thing to do), the comments stand out and make sense, the coding style is kept clean and consistent (something sadly lacking in many otherwise good modules).

    I haven't looked at the code for Brian's other modules (such as Inline, Kwiki and YAML, to name a few), but I assume they are also excellent examples of Perl code, having been written by the same person.

      I will agree that IO::All (with it's use of Spiffy) makes for some clean looking code. However, IO::All is just crammed with everything and the kitchen sink thrown into one module, and even a way to further extend it with plugins!

      Spiffy itself is somewhat questionable in my mind as well since it does so many different things in one module. But after seeing how quickly ingy can whip out new Spiffy based modules, I am less bothered by that fact (usefulness almost always outweighs overly-anal-elegance).

      Back to IO::All, I do have to say that it is very nice when you are writing quick scripts and tools. It takes the headache out of doing some very complex stuff when you just don't have the time to do it the "right" way (the "right" way being a subjective thing). But to use it for any serious sizable project IMO would be inadvisable.

      But of course, this does not mean it is not good code to read :), in fact I rather enjoyed reading it (and learned plenty about obscure IO techniques as well). I would also recommend a look at Spiffy too, it has some rather interesting code in it as well.

      -stvn
Re: What CPAN modules are "good reads"?
by 5mi11er (Deacon) on Jun 14, 2005 at 23:01 UTC
    I've only viewed the source of a few modules, but I've thought that the Date:: modules to be relatively short/easy to understand. However, I've not attempted to view any them using a "the way to code in perl" filter, so whether any of them are well written, I can't comment on.

    I think any module you use effectively a lot is something you can learn from, provided you keep a healthy "grain of salt" attitude toward any given incantation. Whether a given incantation is great or not usually depends on what kind of efficiency filter you happen to be viewing it through.

    -Scott

      The DateTime modules are really nice. Good design, good docs, and what I've seen of the code looks nice too.

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