NAME
Alt - Alternate Module Implementations
SYNOPSIS
PERL_ALT_INSTALL=OVERWRITE cpanm Alt::IO::All::Redux
DESCRIPTION
"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.
THE PROBLEM
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.
THE SOLUTION
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:
PERL_ALT_INSTALL=OVERWRITE 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.
ALT BEST PRACTICES
This idea is new, and the details should be sorted out through proper
discussions. Pull requests welcome.
Here are the basic guidelines for best using the Alt namespace:
Name Creation
Names for alternate modules should be minted like this:
"Alt-$Original_Dist_Name-$phrase"
For instance, if MSTROUT wants to make an alternate IO-All
distribution to have it be Moo-based, he might call it:
Alt-IO-All-Moo
He might also just call it:
Alt-IO-All-MSTROUT
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.
Makefile.PL Changes
Due to experience with problems, it is
important to make your Alt module not install without explicit
direction. You can accomplish this easily in a Makefile.PL, with
something like this:
my $alt = $ENV{PERL_ALT_INSTALL} || '';
$WriteMakefileArgs{DESTDIR} =
$alt ? $alt eq 'OVERWRITE' ? '' : $alt : 'no-install-alt';
Similar techniques should be available for other module release
frameworks.
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:
PERL_ALT_INSTALL=OVERWRITE 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 Alt:: module can be as simple as this:
package Alt::IO::All::MSTROUT;
our $VERSION = '0.01';
no_index
It is important to use the "no_index" directive on the modules you
are providing an alternates for. 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.
Versioning
It is important to not declare a $VERSION in any of the modules that
you are providing alternates for. This will help ensure that your
alternate module does not satisfy the version requirements for
something that wants the real module.
If you want to depend on the alternate versions, then set the
dependency on the "Alt::" module.
NOTE: If you provide an alternate Foo::Bar (with no VERSION) it will
satisfy the version requirements for someone who requires "Foo::Bar
=> 0". In a sense, depending on version 0 means that alternates are
OK.
"use" the Alt
You should add this line to your alternate modules:
use Alt::IO::All::MSTROUT;
That way the Alt:: module gets loaded any time you "use IO::All"
(with the alternate version installed). This gives debugging clues
since the Alt:: module is now in %INC.
Other Concerns
If you have em, I(ngy) would like to know them. Discuss on
#toolchain on irc.perl.org for now.
WHENCE ALT?
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.
AUTHOR
Ingy döt Net
COPYRIGHT
Copyright 2012-2014. Ingy döt Net.
See