1Class::Load(3)        User Contributed Perl Documentation       Class::Load(3)
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NAME

6       Class::Load - A working (require "Class::Name") and more
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VERSION

9       version 0.25
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SYNOPSIS

12           use Class::Load ':all';
13
14           try_load_class('Class::Name')
15               or plan skip_all => "Class::Name required to run these tests";
16
17           load_class('Class::Name');
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19           is_class_loaded('Class::Name');
20
21           my $baseclass = load_optional_class('Class::Name::MightExist')
22               ? 'Class::Name::MightExist'
23               : 'Class::Name::Default';
24

DESCRIPTION

26       "require EXPR" only accepts "Class/Name.pm" style module names, not
27       "Class::Name". How frustrating! For that, we provide "load_class
28       'Class::Name'".
29
30       It's often useful to test whether a module can be loaded, instead of
31       throwing an error when it's not available. For that, we provide
32       "try_load_class 'Class::Name'".
33
34       Finally, sometimes we need to know whether a particular class has been
35       loaded.  Asking %INC is an option, but that will miss inner packages
36       and any class for which the filename does not correspond to the package
37       name. For that, we provide "is_class_loaded 'Class::Name'".
38

FUNCTIONS

40   load_class Class::Name, \%options
41       "load_class" will load "Class::Name" or throw an error, much like
42       "require".
43
44       If "Class::Name" is already loaded (checked with "is_class_loaded")
45       then it will not try to load the class. This is useful when you have
46       inner packages which "require" does not check.
47
48       The %options hash currently accepts one key, "-version". If you specify
49       a version, then this subroutine will call "Class::Name->VERSION(
50       $options{-version} )" internally, which will throw an error if the
51       class's version is not equal to or greater than the version you
52       requested.
53
54       This method will return the name of the class on success.
55
56   try_load_class Class::Name, \%options -> (0|1, error message)
57       Returns 1 if the class was loaded, 0 if it was not. If the class was
58       not loaded, the error will be returned as a second return value in list
59       context.
60
61       Again, if "Class::Name" is already loaded (checked with
62       "is_class_loaded") then it will not try to load the class. This is
63       useful when you have inner packages which "require" does not check.
64
65       Like "load_class", you can pass a "-version" in %options. If the
66       version is not sufficient, then this subroutine will return false.
67
68   is_class_loaded Class::Name, \%options -> 0|1
69       This uses a number of heuristics to determine if the class
70       "Class::Name" is loaded. There heuristics were taken from Class::MOP's
71       old pure-perl implementation.
72
73       Like "load_class", you can pass a "-version" in %options. If the
74       version is not sufficient, then this subroutine will return false.
75
76   load_first_existing_class Class::Name, \%options, ...
77       This attempts to load the first loadable class in the list of classes
78       given. Each class name can be followed by an options hash reference.
79
80       If any one of the classes loads and passes the optional version check,
81       that class name will be returned. If none of the classes can be loaded
82       (or none pass their version check), then an error will be thrown.
83
84       If, when attempting to load a class, it fails to load because of a
85       syntax error, then an error will be thrown immediately.
86
87   load_optional_class Class::Name, \%options -> 0|1
88       "load_optional_class" is a lot like "try_load_class", but also a lot
89       like "load_class".
90
91       If the class exists, and it works, then it will return 1. If you
92       specify a version in %options, then the version check must succeed or
93       it will return 0.
94
95       If the class doesn't exist, and it appears to not exist on disk either,
96       it will return 0.
97
98       If the class exists on disk, but loading from disk results in an error
99       (e.g.: a syntax error), then it will "croak" with that error.
100
101       This is useful for using if you want a fallback module system, i.e.:
102
103           my $class = load_optional_class($foo) ? $foo : $default;
104
105       That way, if $foo does exist, but can't be loaded due to error, you
106       won't get the behaviour of it simply not existing.
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CAVEATS

109       Because of some of the heuristics that this module uses to infer
110       whether a module has been loaded, some false positives may occur in
111       "is_class_loaded" checks (which are also performed internally in other
112       interfaces) -- if a class has started to be loaded but then dies, it
113       may appear that it has already been loaded, which can cause other
114       things to make the wrong decision.  Module::Runtime doesn't have this
115       issue, but it also doesn't do some things that this module does -- for
116       example gracefully handle packages that have been defined inline in the
117       same file as another package.
118

SEE ALSO

120       <http://blog.fox.geek.nz/2010/11/searching-design-spec-for-ultimate.html>
121           This blog post is a good overview of the current state of the
122           existing modules for loading other modules in various ways.
123
124       <http://blog.fox.geek.nz/2010/11/handling-optional-requirements-with.html>
125           This blog post describes how to handle optional modules with
126           Class::Load.
127
128       <http://d.hatena.ne.jp/tokuhirom/20110202/1296598578>
129           This Japanese blog post describes why DBIx::Skinny now uses
130           Class::Load over its competitors.
131
132       Moose, Jifty, Prophet, etc
133           This module was designed to be used anywhere you have "if (eval
134           "require $module"; 1)", which occurs in many large projects.
135
136       Module::Runtime
137           A leaner approach to loading modules
138

SUPPORT

140       Bugs may be submitted through the RT bug tracker
141       <https://rt.cpan.org/Public/Dist/Display.html?Name=Class-Load> (or
142       bug-Class-Load@rt.cpan.org <mailto:bug-Class-Load@rt.cpan.org>).
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144       There is also a mailing list available for users of this distribution,
145       at <http://lists.perl.org/list/moose.html>.
146
147       There is also an irc channel available for users of this distribution,
148       at "#moose" on "irc.perl.org" <irc://irc.perl.org/#moose>.
149

AUTHOR

151       Shawn M Moore <sartak at bestpractical.com>
152

CONTRIBUTORS

154       •   Dave Rolsky <autarch@urth.org>
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156       •   Karen Etheridge <ether@cpan.org>
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158       •   Shawn Moore <sartak@bestpractical.com>
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160       •   Jesse Luehrs <doy@tozt.net>
161
162       •   Kent Fredric <kentfredric@gmail.com>
163
164       •   Paul Howarth <paul@city-fan.org>
165
166       •   Olivier Mengué <dolmen@cpan.org>
167
168       •   Caleb Cushing <xenoterracide@gmail.com>
169

171       This software is copyright (c) 2008 by Shawn M Moore.
172
173       This is free software; you can redistribute it and/or modify it under
174       the same terms as the Perl 5 programming language system itself.
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178perl v5.36.0                      2022-07-22                    Class::Load(3)
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