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Ingy döt Net


Alt - Alternate Module Implementations


    cpanm Alt::IO::All::crackfueled


Alt:: is the namespace for alternate implementations of CPAN modules.

The purpose of the Alt module is to provide documentation explaining the Alt concept, how it works, and guidelines for using it well.


For a given piece of software, CPAN only allows for one implementation of a given module/distribution name.

GitHub on the other hand, is not limited this way. Any author can make a fork, since GitHub repos are namespaced by author id.

On CPAN, even the author(s) of the module in question is limited by this, as they cannot release newer or older forks of their code, without introducing a new name.


A module Foo::Bar is distributed on CPAN as Foo-Bar. It may have submodules like Foo::Bar::Baz.

To make an alternate CPAN version, leave everything exactly the same, except distribute the new version as Alt-Foo-Bar-AltIdentifier.

When a user installs your module like so:

    cpanm Alt::Foo::Bar::better

they will get your version of the Foo::Bar framework (Foo::Bar, Foo::Bar::Baz).

Obviously, this completely overlays the old Foo::Bar install, but that's the whole idea. The user isn't surprised by this because they just asked for an Alternate implementation. If they don't like it, they can simply reinstall the original Foo-Bar, or try some other alternate.


The Alt- concept was thought up by Ingy as he tried to figure out how to revamp the somewhat popular IO::All and YAML.pm modules. Alternates can now be released and alpha/beta tested, while the originals remain stable.

When Alt-IO-All-new is "community approved" it can replace IO-All. If people want the old code, they can can install Alt-IO-All-old.


This idea is new, and the details should be sorted out through proper discussions. Pull requests welcome.

Here are the basic guidelines for using the Alt namespace:

Name Creation

Names for alternate modules should be minted like this:


For instance, if MSTROUT wants to make an alternate IO-All distribution to make it even more crack fueled, he might call it:


He might also just call it:


By having 'Alt' at the start, it guarantees that it does not mess with future IO::All development. The "phrase" at the end can be anything unique to CPAN, but should describe the spirit of the alternate. If the alternate is meant to be short-lived, it can just be the author's CPAN id.

Module for CPAN Indexing

You will need to provide a module like Alt::IO::All::MSTROUT so that CPAN will index something that can cause your distribution to get installed by people:

    cpanm Alt::IO::All::MSTROUT

Since you are adding this module, you should add some doc to it explaining your Alternate version's improvements.


The VERSION of the module you are providing an alternate version of should be the same as the original module at the time you release the alternate. This will make it play well with others.

To use the IO::All example, if MSTROUT releases Alt-IO-All-MSTROUT when IO::All is at version '0.46', his IO::All module should have VERSION = '0.46', but his Alt::IO::All::MSTROUT could be VERSION '0.000005'. This should make the dist be Alt-IO-All-MSTROUT-0.000005.

If another module wants his version of IO::All, it should list Alt::IO::All::MSTROUT 0.000005 as a prereq, and then use IO::All 0.46; in the code.


It is important to use the no_index directive on the modules you are providing an alternative to. This is especially important if you are the author of the original, as PAUSE will reindex CPAN to your Alt- version which defeats the purpose. Even if you are not the same author, it will make your index reports not show failures.

Other Concerns

If you have em, I(ngy) would like to know them. Discuss on #toolchain on irc.perl.org for now.


Ingy döt Net <ingy@cpan.org>


Copyright (c) 2012. Ingy döt Net.

See http://www.perl.com/perl/misc/Artistic.html