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Best(3)		      User Contributed Perl Documentation	       Best(3)

NAME
       Best - Fallbackable module loader

SYNOPSIS
	   # Load the best available YAML module with default imports
	   use Best qw/YAML::Syck YAML/;
	   use Best [ qw/YAML::Syck YAML/ ];   # also works

	   # Load a YAML module and import some symbols
	   use Best [ [ qw/YAML::Syck YAML/ ], qw/DumpFile LoadFile/ ];

	   # And fancier stuff...

	   # Load a new enough YAML module
	   use Best qw/YAML 0.58 YAML::Syck/;
	   use Best [ qw/YAML 0.58 YAML::Syck/ ];
	   use Best [ [ 'YAML' => { version => '0.58' },
			'YAML::Syck' ] ];

	   # Don't load too-new YAML module and import DumpFile
	   use Best [ [ 'YAML' => { ok => sub { YAML->VERSION <= 0.23 } },
			'YAML::Syck', ],
		      qw/DumpFile/ ];

	   # Use the best Carp module w/ different parameter lists
	   use Best [ [ 'Carp::Clan' => { args => [] },
			'Carp' ],
		      qw/croak confess carp cluck/ ];

	   # Choose alternate implementations
	   use Best [ [ 'My::Memoize' => { if => sub { $] <= 5.006 } },
			'Memoize' ],
		      qw/memoize/ ];

	   # Load a CGI module but import nothing
	   use Best [ [ qw/CGI::Simple CGI/ ], [] ];	  # akin to 'use CGI ()'

DESCRIPTION
       Often there are several possible providers of some functionality your
       program needs, but you don't know which is available at the run site.
       For example, one of the modules may be implemented with XS, or not in
       the core Perl distribution and thus not necessarily installed.

       Best attempts to load modules from a list, stopping at the first
       successful load and failing only if no alternative was found.

FUNCTIONS
       Most of the functionality Best provides is on the "use" line; there is
       only one callable functions as such (see "which" below)

       If the arguments are either a simple list or a reference to a simple
       list, the elements are taken to be module names and are loaded in order
       with their default import function called. Any exported symbols are
       installed in the caller package.

	 use Best qw/A Simple List/;
	 use Best [ qw/A Simple List/ ];

   IMPORT LISTS
       If the arguments are a listref with a listref as its first element,
       this interior list is treated as the specification of modules to
       attempt loading, in order; the rest of the arguments are treated as
       options to pass on to the loaded module's import function.

	 use Best [ [ qw/A Simple List/ ],
		    qw/Argument list goes here/ ];
	 use Best [ [ qw/A Simple List/ ],
		    [ qw/Argument list goes here/ ] ];

       To specify a null import ("use Some::Module ()"), pass a zero-element
       listref as the argument list. In the pathological case where you really
       want to load a module and pass it "[]" as an argument, specify "[ [] ]"
       as the argument list to Best.

	 # use Module ();
	 use Best [ [ 'Module' ], [] ];

	 # use Module ( [] );
	 use Best [ [ 'Module' ], [[]] ];

       To customize the import list for a module, use the "args" parameter in
       a hash reference following the module's name.

	 # use Carp::Clan;
	 # use Carp qw/carp croak confess cluck/;
	 use Best [ [ 'Carp::Clan' => { args => [] },
		      'Carp' ],
		    qw/carp croak confess cluck/ ];

   MINIMUM VERSIONS
       You can specify a minimum version for a module by following the module
       name with something that looks like a number or by a hash reference
       with a "version" key.

	 use Best [ [ YAML => '0.58',
		      'YAML::Syck' ] ];

	 use Best [ [ YAML => { version => '0.58' },
		      'YAML::Syck' ] ];

   PRE-VALIDATION
	 use Best Module => { if => CODEREF };

       You may prevent Best from attempting to load a module by providing a
       function as a parameter to "if". The module will only be loaded if your
       function returns a true value.

   POST-VALIDATION
	 use Best Module => { ok => CODEREF };

       You may prevent Best from settling on a successfully loaded module by
       providing a function as a parameter to "ok". Best will follow all of
       its normal rules to attempt to load your module but can be told to
       continue retrying if your function returns false.

   ARBITRARY CODE
       A code reference may be substituted for module names. It will be called
       instead of attempting to load a module. You may do anything you wish in
       this code. It will be skipped if your code throws an exception or
       returns false.

	 use Best [ sub {
			# Decline
			return;
		    },
		    sub {
			# Oops!
			die 'Some error';
		    },
		    'Bad::Module',
		    sub {
			# Ok!
			return 1;
		    }, ];

       which
	   In some cases--for example, class methods in OO modules--you want
	   to know which module Best has successfully loaded. Call
	   "Best->which" with the first in your list of module alternatives;
	   the return value is a string containing the name of the loaded
	   module.

DEPLOYMENT ISSUES
       If you want to use Best because you aren't sure your target machine has
       some modules installed, you may wonder what might warrant the
       assumption that "Best.pm" would be available, since it isn't a core
       module itself.

       One solution is to use Inline::Module to inline "Best.pm" in your
       source code. If you don't know this module, check it out -- after you
       learn what it does, you may decide you don't need Best at all! (If your
       fallback list includes XS modules, though, you may need to stick with
       us.)

       "Best.pm" is pure Perl and a single module with a convenient license,
       so you can also just drop it in your project's "lib" directory.

SEE ALSO
       Module::Load
       UNIVERSAL::require
       Inline::Module

AUTHORS
       Gaal Yahas, "<gaal at forum2.org>"

       Joshua ben Jore, "<jjore at cpan.org>" has made some significant
       contributions.

DIAGNOSTICS
       What modules shall I load?
	   "Best" wasn't given a list of modules to load.

       No viable module found: %s
	   None of the module alternatives loaded.

       Something's wrong!
	   An assertion failed. This means that either there is a bug in the
	   data you fed to Best or a bug in Best.

       The code is scattered with assertions and debugging output that can be
       enabled by putting a true value in the environment variables
       "TRACE_BEST" and "DEBUG_BEST".

       Enabling "TRACE_BEST" also enables the debugging code.

BUGS
       Please report any bugs or feature requests to "bug-template-patch at
       rt.cpan.org", or through the web interface at
       <http://rt.cpan.org/NoAuth/ReportBug.html?Queue=Best>.  I will be
       notified, and then you'll automatically be notified of progress on your
       bug as I make changes.

SUPPORT
       You can find documentation for this module with the perldoc command.

	   perldoc Best

       You can also contact the maintainer at the address above or look for
       information at:

       ·   AnnoCPAN: Annotated CPAN documentation

	   <http://annocpan.org/dist/Best/>

       ·   CPAN Ratings

	   <http://cpanratings.perl.org/d/Best/>

       ·   RT: CPAN's request tracker

	   <http://rt.cpan.org/NoAuth/Bugs.html?Dist=Best>

       ·   Search CPAN

	   <http://search.cpan.org/dist/Best/>

       ·   Source repository

	   <http://svn.openfoundry.org/perlbest/>

COPYRIGHT (The "MIT" License)
       Copyright 2006 Gaal Yahas.

       Permission is hereby granted, free of charge, to any person obtaining a
       copy of this software and associated documentation files (the
       "Software"), to deal in the Software without restriction, including
       without limitation the rights to use, copy, modify, merge, publish,
       distribute, sublicense, and/or sell copies of the Software, and to
       permit persons to whom the Software is furnished to do so, subject to
       the following conditions:

       The above copyright notice and this permission notice shall be included
       in all copies or substantial portions of the Software.

       THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
       OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
       MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
       IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
       CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
       TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
       SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

perl v5.14.1			  2009-01-17			       Best(3)
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