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- =head1 NAME
-
- perlnewmod - preparing a new module for distribution
-
- =head1 DESCRIPTION
-
- This document gives you some suggestions about how to go about writing
- Perl modules, preparing them for distribution, and making them available
- via CPAN.
-
- One of the things that makes Perl really powerful is the fact that Perl
- hackers tend to want to share the solutions to problems they've faced,
- so you and I don't have to battle with the same problem again.
-
- The main way they do this is by abstracting the solution into a Perl
- module. If you don't know what one of these is, the rest of this
- document isn't going to be much use to you. You're also missing out on
- an awful lot of useful code; consider having a look at L<perlmod>,
- L<perlmodlib> and L<perlmodinstall> before coming back here.
-
- When you've found that there isn't a module available for what you're
- trying to do, and you've had to write the code yourself, consider
- packaging up the solution into a module and uploading it to CPAN so that
- others can benefit.
-
- =head2 Warning
-
- We're going to primarily concentrate on Perl-only modules here, rather
- than XS modules. XS modules serve a rather different purpose, and
- you should consider different things before distributing them - the
- popularity of the library you are gluing, the portability to other
- operating systems, and so on. However, the notes on preparing the Perl
- side of the module and packaging and distributing it will apply equally
- well to an XS module as a pure-Perl one.
-
- =head2 What should I make into a module?
-
- You should make a module out of any code that you think is going to be
- useful to others. Anything that's likely to fill a hole in the communal
- library and which someone else can slot directly into their program. Any
- part of your code which you can isolate and extract and plug into
- something else is a likely candidate.
-
- Let's take an example. Suppose you're reading in data from a local
- format into a hash-of-hashes in Perl, turning that into a tree, walking
- the tree and then piping each node to an Acme Transmogrifier Server.
-
- Now, quite a few people have the Acme Transmogrifier, and you've had to
- write something to talk the protocol from scratch - you'd almost
- certainly want to make that into a module. The level at which you pitch
- it is up to you: you might want protocol-level modules analogous to
- L<Net::SMTP|Net::SMTP> which then talk to higher level modules analogous
- to L<Mail::Send|Mail::Send>. The choice is yours, but you do want to get
- a module out for that server protocol.
-
- Nobody else on the planet is going to talk your local data format, so we
- can ignore that. But what about the thing in the middle? Building tree
- structures from Perl variables and then traversing them is a nice,
- general problem, and if nobody's already written a module that does
- that, you might want to modularise that code too.
-
- So hopefully you've now got a few ideas about what's good to modularise.
- Let's now see how it's done.
-
- =head2 Step-by-step: Preparing the ground
-
- Before we even start scraping out the code, there are a few things we'll
- want to do in advance.
-
- =over 3
-
- =item Look around
-
- Dig into a bunch of modules to see how they're written. I'd suggest
- starting with L<Text::Tabs|Text::Tabs>, since it's in the standard
- library and is nice and simple, and then looking at something a little
- more complex like L<File::Copy|File::Copy>. For object oriented
- code, C<WWW::Mechanize> or the C<Email::*> modules provide some good
- examples.
-
- These should give you an overall feel for how modules are laid out and
- written.
-
- =item Check it's new
-
- There are a lot of modules on CPAN, and it's easy to miss one that's
- similar to what you're planning on contributing. Have a good plough
- through the L<http://search.cpan.org> and make sure you're not the one
- reinventing the wheel!
-
- =item Discuss the need
-
- You might love it. You might feel that everyone else needs it. But there
- might not actually be any real demand for it out there. If you're unsure
- about the demand your module will have, consider sending out feelers
- on the C<comp.lang.perl.modules> newsgroup, or as a last resort, ask the
- modules list at C<modules@perl.org>. Remember that this is a closed list
- with a very long turn-around time - be prepared to wait a good while for
- a response from them.
-
- =item Choose a name
-
- Perl modules included on CPAN have a naming hierarchy you should try to
- fit in with. See L<perlmodlib> for more details on how this works, and
- browse around CPAN and the modules list to get a feel of it. At the very
- least, remember this: modules should be title capitalised, (This::Thing)
- fit in with a category, and explain their purpose succinctly.
-
- =item Check again
-
- While you're doing that, make really sure you haven't missed a module
- similar to the one you're about to write.
-
- When you've got your name sorted out and you're sure that your module is
- wanted and not currently available, it's time to start coding.
-
- =back
-
- =head2 Step-by-step: Making the module
-
- =over 3
-
- =item Start with F<module-starter> or F<h2xs>
-
- The F<module-starter> utility is distributed as part of the
- L<Module::Starter|Module::Starter> CPAN package. It creates a directory
- with stubs of all the necessary files to start a new module, according
- to recent "best practice" for module development, and is invoked from
- the command line, thus:
-
- module-starter --module=Foo::Bar \
- --author="Your Name" --email=yourname@cpan.org
-
- If you do not wish to install the L<Module::Starter|Module::Starter>
- package from CPAN, F<h2xs> is an older tool, originally intended for the
- development of XS modules, which comes packaged with the Perl
- distribution.
-
- A typical invocation of L<h2xs|h2xs> for a pure Perl module is:
-
- h2xs -AX --skip-exporter --use-new-tests -n Foo::Bar
-
- The C<-A> omits the Autoloader code, C<-X> omits XS elements,
- C<--skip-exporter> omits the Exporter code, C<--use-new-tests> sets up a
- modern testing environment, and C<-n> specifies the name of the module.
-
- =item Use L<strict|strict> and L<warnings|warnings>
-
- A module's code has to be warning and strict-clean, since you can't
- guarantee the conditions that it'll be used under. Besides, you wouldn't
- want to distribute code that wasn't warning or strict-clean anyway,
- right?
-
- =item Use L<Carp|Carp>
-
- The L<Carp|Carp> module allows you to present your error messages from
- the caller's perspective; this gives you a way to signal a problem with
- the caller and not your module. For instance, if you say this:
-
- warn "No hostname given";
-
- the user will see something like this:
-
- No hostname given at /usr/local/lib/perl5/site_perl/5.6.0/Net/Acme.pm
- line 123.
-
- which looks like your module is doing something wrong. Instead, you want
- to put the blame on the user, and say this:
-
- No hostname given at bad_code, line 10.
-
- You do this by using L<Carp|Carp> and replacing your C<warn>s with
- C<carp>s. If you need to C<die>, say C<croak> instead. However, keep
- C<warn> and C<die> in place for your sanity checks - where it really is
- your module at fault.
-
- =item Use L<Exporter|Exporter> - wisely!
-
- L<Exporter|Exporter> gives you a standard way of exporting symbols and
- subroutines from your module into the caller's namespace. For instance,
- saying C<use Net::Acme qw(&frob)> would import the C<frob> subroutine.
-
- The package variable C<@EXPORT> will determine which symbols will get
- exported when the caller simply says C<use Net::Acme> - you will hardly
- ever want to put anything in there. C<@EXPORT_OK>, on the other hand,
- specifies which symbols you're willing to export. If you do want to
- export a bunch of symbols, use the C<%EXPORT_TAGS> and define a standard
- export set - look at L<Exporter> for more details.
-
- =item Use L<plain old documentation|perlpod>
-
- The work isn't over until the paperwork is done, and you're going to
- need to put in some time writing some documentation for your module.
- C<module-starter> or C<h2xs> will provide a stub for you to fill in; if
- you're not sure about the format, look at L<perlpod> for an
- introduction. Provide a good synopsis of how your module is used in
- code, a description, and then notes on the syntax and function of the
- individual subroutines or methods. Use Perl comments for developer notes
- and POD for end-user notes.
-
- =item Write tests
-
- You're encouraged to create self-tests for your module to ensure it's
- working as intended on the myriad platforms Perl supports; if you upload
- your module to CPAN, a host of testers will build your module and send
- you the results of the tests. Again, C<module-starter> and C<h2xs>
- provide a test framework which you can extend - you should do something
- more than just checking your module will compile.
- L<Test::Simple|Test::Simple> and L<Test::More|Test::More> are good
- places to start when writing a test suite.
-
- =item Write the README
-
- If you're uploading to CPAN, the automated gremlins will extract the
- README file and place that in your CPAN directory. It'll also appear in
- the main F<by-module> and F<by-category> directories if you make it onto
- the modules list. It's a good idea to put here what the module actually
- does in detail, and the user-visible changes since the last release.
-
- =back
-
- =head2 Step-by-step: Distributing your module
-
- =over 3
-
- =item Get a CPAN user ID
-
- Every developer publishing modules on CPAN needs a CPAN ID. Visit
- C<http://pause.perl.org/>, select "Request PAUSE Account", and wait for
- your request to be approved by the PAUSE administrators.
-
- =item C<perl Makefile.PL; make test; make dist>
-
- Once again, C<module-starter> or C<h2xs> has done all the work for you.
- They produce the standard C<Makefile.PL> you see when you download and
- install modules, and this produces a Makefile with a C<dist> target.
-
- Once you've ensured that your module passes its own tests - always a
- good thing to make sure - you can C<make dist>, and the Makefile will
- hopefully produce you a nice tarball of your module, ready for upload.
-
- =item Upload the tarball
-
- The email you got when you received your CPAN ID will tell you how to
- log in to PAUSE, the Perl Authors Upload SErver. From the menus there,
- you can upload your module to CPAN.
-
- =item Announce to the modules list
-
- Once uploaded, it'll sit unnoticed in your author directory. If you want
- it connected to the rest of the CPAN, you'll need to go to "Register
- Namespace" on PAUSE. Once registered, your module will appear in the
- by-module and by-category listings on CPAN.
-
- =item Announce to clpa
-
- If you have a burning desire to tell the world about your release, post
- an announcement to the moderated C<comp.lang.perl.announce> newsgroup.
-
- =item Fix bugs!
-
- Once you start accumulating users, they'll send you bug reports. If
- you're lucky, they'll even send you patches. Welcome to the joys of
- maintaining a software project...
-
- =back
-
- =head1 AUTHOR
-
- Simon Cozens, C<simon@cpan.org>
-
- Updated by Kirrily "Skud" Robert, C<skud@cpan.org>
-
- =head1 SEE ALSO
-
- L<perlmod>, L<perlmodlib>, L<perlmodinstall>, L<h2xs>, L<strict>,
- L<Carp>, L<Exporter>, L<perlpod>, L<Test::Simple>, L<Test::More>
- L<ExtUtils::MakeMaker>, L<Module::Build>, L<Module::Starter>
- http://www.cpan.org/ , Ken Williams' tutorial on building your own
- module at http://mathforum.org/~ken/perl_modules.html
-