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Best - Load modules with fallback
Contents
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.
Copyright (The "Mit (X11)" License)
Copyright (C) 2006-2024 Gaal Yahas
This program is distributed under the MIT (X11) License:
<http://www.opensource.org/licenses/mit-license.php>
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 v5.40.0 2024-09-21 Best(3pm)
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.
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.
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.
Functions
Most of the functionality Best provides is on the "use" line; there is only one callable method 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/ ];
IMPORTLISTS
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/ ];
MINIMUMVERSIONS
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.
ARBITRARYCODE
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.
use Best qw/YAML::Syck YAML/;
print "Fallback" if Best->which('YAML::Syck') eq 'YAML';
Name
Best - Load modules with fallback
See Also
Module::Load
UNIVERSAL::require
Inline::Module
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
<https://github.com/gaal/best>
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 ()'
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