1Best(3) User Contributed Perl Documentation Best(3)
2
6 Best - Load modules with fallback
7
9 # Load the best available YAML module with default imports
10 use Best qw/YAML::Syck YAML/;
11 use Best [ qw/YAML::Syck YAML/ ]; # also works
12 # Load a YAML module and import some symbols
14 use Best [ [ qw/YAML::Syck YAML/ ], qw/DumpFile LoadFile/ ];
15 # And fancier stuff...
17 # Load a new enough YAML module
19 use Best qw/YAML 0.58 YAML::Syck/;
20 use Best [ qw/YAML 0.58 YAML::Syck/ ];
21 use Best [ [ 'YAML' => { version => '0.58' },
22 'YAML::Syck' ] ];
23 # Don't load too-new YAML module and import DumpFile
25 use Best [ [ 'YAML' => { ok => sub { YAML->VERSION <= 0.23 } },
26 'YAML::Syck', ],
27 qw/DumpFile/ ];
28 # Use the best Carp module w/ different parameter lists
30 use Best [ [ 'Carp::Clan' => { args => [] },
31 'Carp' ],
32 qw/croak confess carp cluck/ ];
33 # Choose alternate implementations
35 use Best [ [ 'My::Memoize' => { if => sub { $] <= 5.006 } },
36 'Memoize' ],
37 qw/memoize/ ];
38 # Load a CGI module but import nothing
40 use Best [ [ qw/CGI::Simple CGI/ ], [] ]; # akin to 'use CGI ()'
41
43 Often there are several possible providers of some functionality your
44 program needs, but you don't know which is available at the run site.
45 For example, one of the modules may be implemented with XS, or not in
46 the core Perl distribution and thus not necessarily installed.
47 Best attempts to load modules from a list, stopping at the first
49 successful load and failing only if no alternative was found.
50
52 Most of the functionality Best provides is on the "use" line; there is
53 only one callable functions as such (see "which" below)
54 If the arguments are either a simple list or a reference to a simple
56 list, the elements are taken to be module names and are loaded in order
57 with their default import function called. Any exported symbols are
58 installed in the caller package.
59 use Best qw/A Simple List/;
61 use Best [ qw/A Simple List/ ];
62 IMPORT LISTS
64 If the arguments are a listref with a listref as its first element,
65 this interior list is treated as the specification of modules to
66 attempt loading, in order; the rest of the arguments are treated as
67 options to pass on to the loaded module's import function.
68 use Best [ [ qw/A Simple List/ ],
70 qw/Argument list goes here/ ];
71 use Best [ [ qw/A Simple List/ ],
72 [ qw/Argument list goes here/ ] ];
73 To specify a null import ("use Some::Module ()"), pass a zero-element
75 listref as the argument list. In the pathological case where you really
76 want to load a module and pass it "[]" as an argument, specify "[ [] ]"
77 as the argument list to Best.
78 # use Module ();
80 use Best [ [ 'Module' ], [] ];
81 # use Module ( [] );
83 use Best [ [ 'Module' ], [[]] ];
84 To customize the import list for a module, use the "args" parameter in
86 a hash reference following the module's name.
87 # use Carp::Clan;
89 # use Carp qw/carp croak confess cluck/;
90 use Best [ [ 'Carp::Clan' => { args => [] },
91 'Carp' ],
92 qw/carp croak confess cluck/ ];
93 MINIMUM VERSIONS
95 You can specify a minimum version for a module by following the module
96 name with something that looks like a number or by a hash reference
97 with a "version" key.
98 use Best [ [ YAML => '0.58',
100 'YAML::Syck' ] ];
101 use Best [ [ YAML => { version => '0.58' },
103 'YAML::Syck' ] ];
104 PRE-VALIDATION
106 use Best Module => { if => CODEREF };
107 You may prevent Best from attempting to load a module by providing a
109 function as a parameter to "if". The module will only be loaded if your
110 function returns a true value.
111 POST-VALIDATION
113 use Best Module => { ok => CODEREF };
114 You may prevent Best from settling on a successfully loaded module by
116 providing a function as a parameter to "ok". Best will follow all of
117 its normal rules to attempt to load your module but can be told to
118 continue retrying if your function returns false.
119 ARBITRARY CODE
121 A code reference may be substituted for module names. It will be called
122 instead of attempting to load a module. You may do anything you wish in
123 this code. It will be skipped if your code throws an exception or
124 returns false.
125 use Best [ sub {
127 # Decline
128 return;
129 },
130 sub {
131 # Oops!
132 die 'Some error';
133 },
134 'Bad::Module',
135 sub {
136 # Ok!
137 return 1;
138 }, ];
139 which
141 In some cases--for example, class methods in OO modules--you want
142 to know which module Best has successfully loaded. Call
143 "Best->which" with the first in your list of module alternatives;
144 the return value is a string containing the name of the loaded
145 module.
146
148 If you want to use Best because you aren't sure your target machine has
149 some modules installed, you may wonder what might warrant the
150 assumption that "Best.pm" would be available, since it isn't a core
151 module itself.
152 One solution is to use Inline::Module to inline "Best.pm" in your
154 source code. If you don't know this module, check it out -- after you
155 learn what it does, you may decide you don't need Best at all! (If your
156 fallback list includes XS modules, though, you may need to stick with
157 us.)
158 "Best.pm" is pure Perl and a single module with a convenient license,
160 so you can also just drop it in your project's "lib" directory.
161
163 Module::Load
164 UNIVERSAL::require
165 Inline::Module
166
168 Gaal Yahas, "<gaal at forum2.org>"
169 Joshua ben Jore, "<jjore at cpan.org>" has made some significant
171 contributions.
172
174 What modules shall I load?
175 "Best" wasn't given a list of modules to load.
176 No viable module found: %s
178 None of the module alternatives loaded.
179 Something's wrong!
181 An assertion failed. This means that either there is a bug in the
182 data you fed to Best or a bug in Best.
183 The code is scattered with assertions and debugging output that can be
185 enabled by putting a true value in the environment variables
186 "TRACE_BEST" and "DEBUG_BEST".
187 Enabling "TRACE_BEST" also enables the debugging code.
189
191 Please report any bugs or feature requests to "bug-template-patch at
192 rt.cpan.org", or through the web interface at
193 <http://rt.cpan.org/NoAuth/ReportBug.html?Queue=Best>. I will be
194 notified, and then you'll automatically be notified of progress on your
195 bug as I make changes.
196
198 You can find documentation for this module with the perldoc command.
199 perldoc Best
201 You can also contact the maintainer at the address above or look for
203 information at:
204 · AnnoCPAN: Annotated CPAN documentation
206 <http://annocpan.org/dist/Best/>
208 · CPAN Ratings
210 <http://cpanratings.perl.org/d/Best/>
212 · RT: CPAN's request tracker
214 <http://rt.cpan.org/NoAuth/Bugs.html?Dist=Best>
216 · Search CPAN
218 <http://search.cpan.org/dist/Best/>
220 · Source repository
222 <https://github.com/gaal/best>
224
226 Copyright (C) 2006-2012 Gaal Yahas
227 This program is distributed under the MIT (X11) License:
229 <http://www.opensource.org/licenses/mit-license.php>
230 Permission is hereby granted, free of charge, to any person obtaining a
232 copy of this software and associated documentation files (the
233 "Software"), to deal in the Software without restriction, including
234 without limitation the rights to use, copy, modify, merge, publish,
235 distribute, sublicense, and/or sell copies of the Software, and to
236 permit persons to whom the Software is furnished to do so, subject to
237 the following conditions:
238 The above copyright notice and this permission notice shall be included
240 in all copies or substantial portions of the Software.
241 THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
243 OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
244 MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
245 IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
246 CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
247 TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
248 SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
249perl v5.32.0 2020-07-28 Best(3)