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Class::Load(3) User Contributed Perl Documentation Class::Load(3)
NAME
Class::Load - a working (require "Class::Name") and more
VERSION
version 0.20
SYNOPSIS
use Class::Load ':all';
try_load_class('Class::Name')
or plan skip_all => "Class::Name required to run these tests";
load_class('Class::Name');
is_class_loaded('Class::Name');
my $baseclass = load_optional_class('Class::Name::MightExist')
? 'Class::Name::MightExist'
: 'Class::Name::Default';
DESCRIPTION
"require EXPR" only accepts "Class/Name.pm" style module names, not "Class::Name". How
frustrating! For that, we provide "load_class 'Class::Name'".
It's often useful to test whether a module can be loaded, instead of throwing an error
when it's not available. For that, we provide "try_load_class 'Class::Name'".
Finally, sometimes we need to know whether a particular class has been loaded. Asking
%INC is an option, but that will miss inner packages and any class for which the filename
does not correspond to the package name. For that, we provide "is_class_loaded
'Class::Name'".
FUNCTIONS
load_class Class::Name, \%options
"load_class" will load "Class::Name" or throw an error, much like "require".
If "Class::Name" is already loaded (checked with "is_class_loaded") then it will not try
to load the class. This is useful when you have inner packages which "require" does not
check.
The %options hash currently accepts one key, "-version". If you specify a version, then
this subroutine will call "Class::Name->VERSION( $options{-version} )" internally, which
will throw an error if the class's version is not equal to or greater than the version you
requested.
This method will return the name of the class on success.
try_load_class Class::Name, \%options -> (0|1, error message)
Returns 1 if the class was loaded, 0 if it was not. If the class was not loaded, the error
will be returned as a second return value in list context.
Again, if "Class::Name" is already loaded (checked with "is_class_loaded") then it will
not try to load the class. This is useful when you have inner packages which "require"
does not check.
Like "load_class", you can pass a "-version" in %options. If the version is not
sufficient, then this subroutine will return false.
is_class_loaded Class::Name, \%options -> 0|1
This uses a number of heuristics to determine if the class "Class::Name" is loaded. There
heuristics were taken from Class::MOP's old pure-perl implementation.
Like "load_class", you can pass a "-version" in %options. If the version is not
sufficient, then this subroutine will return false.
load_first_existing_class Class::Name, \%options, ...
This attempts to load the first loadable class in the list of classes given. Each class
name can be followed by an options hash reference.
If any one of the classes loads and passes the optional version check, that class name
will be returned. If none of the classes can be loaded (or none pass their version check),
then an error will be thrown.
If, when attempting to load a class, it fails to load because of a syntax error, then an
error will be thrown immediately.
load_optional_class Class::Name, \%options -> 0|1
"load_optional_class" is a lot like "try_load_class", but also a lot like "load_class".
If the class exists, and it works, then it will return 1. If you specify a version in
%options, then the version check must succeed or it will return 0.
If the class doesn't exist, and it appears to not exist on disk either, it will return 0.
If the class exists on disk, but loading from disk results in an error ( i.e.: a syntax
error ), then it will "croak" with that error.
This is useful for using if you want a fallback module system, i.e.:
my $class = load_optional_class($foo) ? $foo : $default;
That way, if $foo does exist, but can't be loaded due to error, you won't get the
behaviour of it simply not existing.
SEE ALSO
<http://blog.fox.geek.nz/2010/11/searching-design-spec-for-ultimate.html>
This blog post is a good overview of the current state of the existing modules for
loading other modules in various ways.
<http://blog.fox.geek.nz/2010/11/handling-optional-requirements-with.html>
This blog post describes how to handle optional modules with Class::Load.
<http://d.hatena.ne.jp/tokuhirom/20110202/1296598578>
This Japanese blog post describes why DBIx::Skinny now uses Class::Load over its
competitors.
Moose, Jifty, Prophet, etc
This module was designed to be used anywhere you have "if (eval "require $module";
1)", which occurs in many large projects.
AUTHOR
Shawn M Moore <sartak at bestpractical.com>
COPYRIGHT AND LICENSE
This software is copyright (c) 2012 by Shawn M Moore.
This is free software; you can redistribute it and/or modify it under the same terms as
the Perl 5 programming language system itself.
perl v5.16.3 2012-07-15 Class::Load(3)
Generated by $Id: phpMan.php,v 4.55 2007/09/05 04:42:51 chedong Exp $ Author: Che Dong
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