NAME
    Alien - External libraries wrapped up for your viewing pleasure!

SYNOPSIS
     perldoc Alien;

DESCRIPTION
    Alien is a package that exists just to hold together an idea, the idea
    of Alien:: packages, so there is no code here, just motivation for
    Alien.

    The intent of Alien is to provide a mechanism for specifying, installing
    and using non-native dependencies on CPAN. Frequently, this is a C
    library used by XS, but it could be anything non-Perl usable from Perl.
    Typical characteristics of an Alien distribution include:

    Probe for or install library during the build process
        Usually this means that Module::Build or ExtUtils::MakeMaker will be
        extended to probe for an existing system library that meets the
        criteria of the Alien module. If it cannot be found the library is
        downloaded from the Internet and installed into a share directory
        (See File::ShareDir).

        Usually, though not necessarily, this is a C library. It could be
        anything though, some JavaScript, Java ".class" files. Anything
        imaginable.

    The module itself provides attributes needed to use the library
        This means that if you are writing "Alien::Foo" it will provide
        class or member functions that will provide the necessary
        information for using the library that was probed for or installed
        during the previous step.

        If, for example, "Alien::Foo" were providing a dependency on the C
        library "libfoo", then you might provide "Alien::Foo->cflags" and
        "Alien::Foo->libs" class methods to return the compiler and library
        flags required for using the library.

    These are suggestions only, and this module does not provide a
    framework, because the needs of a non-native dependency on CPAN are
    potentially quite diverse. That being said, if your library uses a
    standard build system, like "autoconf", "make" or "CMake" you should
    consider using Alien::Base which makes it easy to write Alien modules
    that work with many common types of package build systems.

CAVEATS
    This section contains some recommendations from my own experience in
    writing Alien modules and from working on the Alien::Base team.

    When building from source code, build static libraries whenever possible
        Or at least isolate the dynamic libraries so they can be used by
        FFI, but do not use them to build XS modules. The reason for this is
        that if an end user upgrades their version of "Alien::Foo" it may
        break the already installed version of "Foo::XS" that used it when
        it was installed.

    On Windows (ActiveState, Strawberry Perl)
        Many open source libraries use "autoconf" and other Unix focused
        tools that may not be easily available to the native (non-Cygwin)
        windows Perl. Alien::MSYS provides just enough of these tools for
        "autoconf" and may be sufficient for some other build tools. Also,
        Alien::Base has hooks to detect "autoconf" and inject Alien::MSYS as
        a requirement on Windows when it is needed.

    MB vs EUMM
        The original Alien documentation recommends the use of Module::Build
        (MB), which at the time was recommended over ExtUtils::MakeMaker
        (EUMM). Many Alien distributions have been written using MB
        (including Alien::Base). I believe this is because it is an easier
        build system to adapt to the Alien concept. It should be noted that
        MB is no longer universally recommended over EUMM.

ORIGINAL MANIFESTO
    What follows is the original Alien manifesto written by Artur Bergman.
    It is included here, because much of it is still largely true today, but
    it was out of necessity quite aspirational at the time it was written.

  Why
    James and I ended up doing a build system for Fotango, lots of people
    have done a build system, it is a pretty boring task. The boring task is
    really all the mindlessly stupid things you need to do to build C
    libraries that Perl modules require, these C modules usually have
    unusual installation systems or require vastly different options. So
    CPAN modules install easy, 3rd party stuff is nasty.

    So, suddenly an idea struck me, Alien packages! Imagine a CPAN module
    that has as its only task to make sure a certain library is installed!
    That means that you can write all the voodoo in your Build.PL file and
    then just make sure the module requires the correct Alien module! Then
    anything that install Perl modules will deal with it automatically!

  How
    So, what should an Alien module do? It should make sure that the target
    is installed and it should provide the caller with enough information to
    use it.

    The idea is that you use it to make sure it is there, and you call class
    methods to find out what to use. These class methods will be
    individually specified by the stand alone Alien modules.

  No Framework!
    The reason this is so loosely worded is because we have no idea what
    common functionality will be needed, so we will let evolution work for
    us and see what individual Alien packages need and then eventually
    factor it out into this packages. I would like to avoid a top down
    design approach.

  Responsibilities of a Alien module.
    On installation, make sure the required package is there, otherwise
    install it.

    On usage, make sure the required package is there, else croak.

    Bundle the source with the module, or download it.

    Allow module authors to access information it gathers.

    Document itself well.

    Preferably use Module::Build. [ see caveats above ]

    Be sane.

SUPPORT
    No support needed.

AUTHOR
    Arthur Bergman <abergman@fotango.com>
    Graham Ollis <plicease@cpan.org>

COPYRIGHT
    This program is free software; you can redistribute it and/or modify it
    under the same terms as Perl itself.

    The full text of the license can be found in the LICENSE file included
    with this module.

SEE ALSO
    Alien::Base
        An (optional) base class and framework for creating Alien
        distributions.

    Alien::Base::FAQ
        Frequently Asked Questions for Alien::Base. Mostly specific to
        Alien::Base, but also addresses some challenges for Alien in
        general.

    #native on irc.perl.org <http://chat.mibbit.com/#native@irc.perl.org>
        This channel on IRC is dedicated to those interested in using native
        interfaces in Perl. It is specifically geared to Alien, Alien::Base
        and FFI.

    Perl5 Alien mailing list
    <https://groups.google.com/forum/#!forum/perl5-alien>
        This mailing list is mainly for Alien::Base, and announcements for
        new versions will be posted there, but general Alien inquires are
        also welcome.

