1Class::Autouse(3)     User Contributed Perl Documentation    Class::Autouse(3)
2
3
4

NAME

6       Class::Autouse - Run-time load a class the first time you call a method
7       in it.
8

SYNOPSIS

10           ##################################################################
11           # SAFE FEATURES
12
13           # Debugging (if you go that way) must be set before the first use
14           BEGIN {
15               $Class::Autouse::DEBUG = 1;
16           }
17
18           # Turn on developer mode (always load immediately)
19           use Class::Autouse qw{:devel};
20
21           # Load a class on method call
22           use Class::Autouse;
23           Class::Autouse->autouse( 'CGI' );
24           print CGI->b('Wow!');
25
26           # Use as a pragma
27           use Class::Autouse qw{CGI};
28
29           # Use a whole module tree
30           Class::Autouse->autouse_recursive('Acme');
31
32           # Disable module-existance check, and thus one additional 'stat'
33           # per module, at autouse-time if loading modules off a remote
34           # network drive such as NFS or SMB.
35           # (See below for other performance optimizations.)
36           use Class::Autouse qw{:nostat};
37
38
39
40
41
42           ##################################################################
43           # UNSAFE FEATURES
44
45           # Turn on the Super Loader (load all classes on demand)
46           use Class::Autouse qw{:superloader};
47
48           # Autouse classes matching a given regular expression
49           use Class::Autouse qr/::Test$/;
50
51           # Install a class generator (instead of overriding UNIVERSAL::AUTOLOAD)
52           # (See below for a detailed example)
53           use Class::Autouse \&my_class_generator;
54
55           # Add a manual callback to UNIVERSAL::AUTOLOAD for syntactic sugar
56           Class::Autouse->sugar(\&my_magic);
57

DESCRIPTION

59       Class::Autouse is a runtime class loader that allows you to specify
60       classes that will only load when a method of that class is called.
61
62       For large classes or class trees that might not be used during the
63       running of a program, such as Date::Manip, this can save you large
64       amounts of memory, and decrease the script load time a great deal.
65
66       Class::Autouse also provides a number of "unsafe" features for runtime
67       generation of classes and implementation of syntactic sugar. These
68       features make use of (evil) UNIVERSAL::AUTOLOAD hooking, and are
69       implemented in this class because these hooks can only be done by a one
70       module, and Class::Autouse serves as a useful place to centralise this
71       kind of evil :)
72
73   Class, not Module
74       The terminology "class loading" instead of "module loading" is used
75       intentionally. Modules will only be loaded if they are acting as a
76       class.
77
78       That is, they will only be loaded during a Class->method call. If you
79       try to use a subroutine directly, say with "Class::method()", the class
80       will not be loaded and a fatal error will mostly likely occur.
81
82       This limitation is made to allow more powerfull features in other
83       areas, because we can focus on just loading the modules, and not have
84       to deal with importing.
85
86       And really, if you are doing OO Perl, you should be avoiding importing
87       wherever possible.
88
89   Use as a pragma
90       Class::Autouse can be used as a pragma, specifying a list of classes to
91       load as the arguments. For example
92
93          use Class::Autouse qw{CGI Data::Manip This::That};
94
95       is equivalent to
96
97          use Class::Autouse;
98          Class::Autouse->autouse( 'CGI'         );
99          Class::Autouse->autouse( 'Data::Manip' );
100          Class::Autouse->autouse( 'This::That'  );
101
102   Developer Mode
103       "Class::Autouse" features a developer mode. In developer mode, classes
104       are loaded immediately, just like they would be with a normal 'use'
105       statement (although the import sub isn't called).
106
107       This allows error checking to be done while developing, at the expense
108       of a larger memory overhead. Developer mode is turned on either with
109       the "devel" method, or using :devel in any of the pragma arguments.
110       For example, this would load CGI.pm immediately
111
112           use Class::Autouse qw{:devel CGI};
113
114       While developer mode is roughly equivalent to just using a normal use
115       command, for a large number of modules it lets you use autoloading
116       notation, and just comment or uncomment a single line to turn developer
117       mode on or off. You can leave it on during development, and turn it off
118       for speed reasons when deploying.
119
120   Recursive Loading
121       As an alternative to the super loader, the "autouse_recursive" and
122       "load_recursive" methods can be used to autouse or load an entire tree
123       of classes.
124
125       For example, the following would give you access to all the URI related
126       classes installed on the machine.
127
128           Class::Autouse->autouse_recursive( 'URI' );
129
130       Please note that the loadings will only occur down a single branch of
131       the include path, whichever the top class is located in.
132
133   No-Stat Mode
134       For situations where a module exists on a remote disk or another
135       relatively expensive location, you can call "Class::Autouse" with the
136       :nostat param to disable initial file existance checking at hook time.
137
138         # Disable autoload-time file existance checking
139         use Class::Autouse qw{:nostat};
140
141   Super Loader Mode
142       Turning on the "Class::Autouse" super loader allows you to
143       automatically load ANY class without specifying it first. Thus, the
144       following will work and is completely legal.
145
146           use Class::Autouse qw{:superloader};
147
148           print CGI->b('Wow!');
149
150       The super loader can be turned on with either the
151       "Class::Autouse->"superloader> method, or the ":superloader" pragma
152       argument.
153
154       Please note that unlike the normal one-at-a-time autoloading, the
155       super-loader makes global changes, and so is not completely self-
156       contained.
157
158       It has the potential to cause unintended effects at a distance. If you
159       encounter unusual behaviour, revert to autousing one-at-a-time, or use
160       the recursive loading.
161
162       Use of the Super Loader is highly discouraged for widely distributed
163       public applications or modules unless unavoidable. Do not use just to
164       be lazy and save a few lines of code.
165
166   Loading with Regular Expressions
167       As another alternative to the superloader and recursive loading, a
168       compiled regular expression (qr//) can be supplied as a loader.  Note
169       that this loader implements UNIVERSAL::AUTOLOAD, and has the same side
170       effects as the superloader.
171
172   Registering a Callback for Dynamic Class Creation
173       If none of the above are sufficient, a CODE reference can be given to
174       Class::Autouse.  Any attempt to call a method on a missing class will
175       launch each registered callback until one returns true.
176
177       Since overriding UNIVERSAL::AUTOLOAD can be done only once in a given
178       Perl application, this feature allows UNIVERSAL::AUTOLOAD to be shared.
179       Please use this instead of implementing your own UNIVERSAL::AUTOLOAD.
180
181       See the warnings under the "Super Loader Module" above which apply to
182       all of the features which override UNIVERSAL::AUTOLOAD.
183
184       It is up to the callback to define the class, the details of which are
185       beyond the scope of this document.   See the example below for a quick
186       reference:
187
188       Callback Example
189
190       Any use of a class like Foo::Wrapper autogenerates that class as a
191       proxy around Foo.
192
193           use Class::Autouse sub {
194               my ($class) = @_;
195               if ($class =~ /(^.*)::Wrapper/) {
196                   my $wrapped_class = $1;
197                   eval "package $class; use Class::AutoloadCAN;";
198                   die $@ if $@;
199                   no strict 'refs';
200                   *{$class . '::new' } = sub {
201                       my $class = shift;
202                       my $proxy = $wrapped_class->new(@_);
203                       my $self = bless({proxy => $proxy},$class);
204                       return $self;
205                   };
206                   *{$class . '::CAN' } = sub {
207                       my ($obj,$method) = @_;
208                       my $delegate = $wrapped_class->can($method);
209                       return unless $delegate;
210                       my $delegator = sub {
211                           my $self = shift;
212                           if (ref($self)) {
213                               return $self->{proxy}->$method(@_);
214                           }
215                           else {
216                               return $wrapped_class->$method(@_);
217                           }
218                       };
219                       return *{ $class . '::' . $method } = $delegator;
220                   };
221
222                   return 1;
223               }
224               return;
225           };
226
227           package Foo;
228           sub new { my $class = shift; bless({@_},$class); }
229           sub class_method { 123 }
230           sub instance_method {
231               my ($self,$v) = @_;
232               return $v * $self->some_property
233           }
234           sub some_property { shift->{some_property} }
235
236
237           package main;
238           my $x = Foo::Wrapper->new(
239               some_property => 111,
240           );
241           print $x->some_property,"\n";
242           print $x->instance_method(5),"\n";
243           print Foo::Wrapper->class_method,"\n";
244
245   sugar
246       This method is provided to support "syntactic sugar": allowing the
247       developer to put things into Perl which do not look like regular Perl.
248       There are several ways to do this in Perl.  Strategies which require
249       overriding UNIVERSAL::AUTOLOAD can use this interface instead to share
250       that method with the superloader, and with class gnerators.
251
252       When Perl is unable to find a subroutine/method, and all of the class
253       loaders are exhausted, callbacks registered via sugar() are called.
254       The callbacks recieve the class name, method name, and parameters of
255       the call.
256
257       If the callback returns nothing, Class::Autouse will continue to
258       iterate through other callbacks.  The first callback which returns a
259       true value will end iteration.  That value is expected to be a CODE
260       reference which will respond to the AUTOLOAD call.
261
262       Note: The sugar callback(s) will only be fired by UNIVERSAL::AUTOLOAD
263       after all other attempts at loading the class are done, and after
264       attempts to use regular AUTOLOAD to handle the method call.  It is
265       never fired by isa() or can().  It will fire repatedly for the same
266       class.  To generate classes, use the regular CODE ref support in
267       autouse().
268
269       Syntactic Sugar Example
270
271           use Class::Autouse;
272           Class::Autouse->sugar(
273               sub {
274                   my $caller = caller(1);
275                   my ($class,$method,@params) = @_;
276                   shift @params;
277                   my @words = ($method,$class,@params);
278                   my $sentence = join(" ",@words);
279                   return sub { $sentence };
280               }
281           );
282
283           $x = trolls have big ugly hairy feet;
284
285           print $x,"\n";
286           # trolls have big ugly hairy feet
287
288   mod_perl
289       The mechanism that "Class::Autouse" uses is not compatible with
290       mod_perl.  In particular with reloader modules like Apache::Reload.
291       "Class::Autouse" detects the presence of mod_perl and acts as normal,
292       but will always load all classes immediately, equivalent to having
293       developer mode enabled.
294
295       This is actually beneficial, as under mod_perl classes should be
296       preloaded in the parent mod_perl process anyway, to prevent them having
297       to be loaded by the Apache child classes. It also saves HUGE amounts of
298       memory.
299
300       Note that dynamically generated classes and classes loaded via regex
301       CANNOT be pre-loaded automatically before forking child processes.
302       They will still be loaded on demand, often in the child process.  See
303       prefork below.
304
305   prefork
306       As with mod_perl, "Class::Autouse" is compatible with the prefork
307       module, and all modules specifically autoloaded will be loaded before
308       forking correctly, when requested by prefork.
309
310       Since modules generated via callback or regex cannot be loaded
311       automatically by prefork in a generic way, it's advised to use prefork
312       directly to load/generate classes when using mod_perl.
313
314   Performance Optimizatons
315       :nostat
316           Described above, this option is useful when the module in question
317           is on remote disk.
318
319       :noprebless
320           When set, Class::Autouse presumes that objects which are already
321           blessed have their class loaded.
322
323           This is true in most cases, but will break if the developer intends
324           to reconstitute serialized objects from Data::Dumper, FreezeThaw or
325           its cousins, and has configured Class::Autouse to load the involved
326           classes just-in-time.
327
328       :staticisa
329           When set, presumes that @ISA will not change for a class once it is
330           loaded.  The greatest grandparent of a class will be given back the
331           original can/isa implementations which are faster than those
332           Class::Autouse installs into UNIVERSAL.  This is a performance
333           tweak useful in most cases, but is left off by default to prevent
334           obscure bugs.
335
336   The Internal Debugger
337       Class::Autouse provides an internal debugger, which can be used to
338       debug any weird edge cases you might encounter when using it.
339
340       If the $Class::Autouse::DEBUG variable is true when "Class::Autouse" is
341       first loaded, debugging will be compiled in. This debugging prints
342       output like the following to STDOUT.
343
344           Class::Autouse::autouse_recursive( 'Foo' )
345               Class::Autouse::_recursive( 'Foo', 'load' )
346                   Class::Autouse::load( 'Foo' )
347                   Class::Autouse::_children( 'Foo' )
348                   Class::Autouse::load( 'Foo::Bar' )
349                       Class::Autouse::_file_exists( 'Foo/Bar.pm' )
350                       Class::Autouse::load -> Loading in Foo/Bar.pm
351                   Class::Autouse::load( 'Foo::More' )
352                       etc...
353
354       Please note that because this is optimised out if not used, you can no
355       longer (since 1.20) enable debugging at run-time. This decision was
356       made to remove a large number of unneeded branching and speed up
357       loading.
358

METHODS

360   autouse $class, ...
361       The autouse method sets one or more classes to be loaded as required.
362
363   load $class
364       The load method loads one or more classes into memory. This is
365       functionally equivalent to using require to load the class list in,
366       except that load will detect and remove the autoloading hook from a
367       previously autoused class, whereas as use effectively ignore the class,
368       and not load it.
369
370   devel
371       The devel method sets development mode on (argument of 1) or off
372       (argument of 0).
373
374       If any classes have previously been autouse'd and not loaded when this
375       method is called, they will be loaded immediately.
376
377   superloader
378       The superloader method turns on the super loader.
379
380       Please note that once you have turned the superloader on, it cannot be
381       turned off. This is due to code that might be relying on it being there
382       not being able to autoload its classes when another piece of code
383       decides they don't want it any more, and turns the superloader off.
384
385   class_exists $class
386       Handy method when doing the sort of jobs that "Class::Autouse" does.
387       Given a class name, it will return true if the class can be loaded (
388       i.e. in @INC ), false if the class can't be loaded, and undef if the
389       class name is invalid.
390
391       Note that this does not actually load the class, just tests to see if
392       it can be loaded. Loading can still fail. For a more comprehensive set
393       of methods of this nature, see Class::Inspector.
394
395   autouse_recursive $class
396       The same as the "autouse" method, but autouses recursively.
397
398   load_recursive $class
399       The same as the "load" method, but loads recursively. Great for
400       checking that a large class tree that might not always be loaded will
401       load correctly.
402

SUPPORT

404       Bugs should be always be reported via the CPAN bug tracker at
405
406       <http://rt.cpan.org/NoAuth/ReportBug.html?Queue=Class-Autouse>
407
408       For other issues, or commercial enhancement or support, contact the
409       author.
410

AUTHORS

412       Adam Kennedy <cpan@ali.as>
413
414       Scott Smith <sakoht@cpan.org>
415
416       Rob Napier <rnapier@employees.org>
417

SEE ALSO

419       autoload, autoclass
420
422       Copyright 2002 - 2012 Adam Kennedy.
423
424       This program is free software; you can redistribute it and/or modify it
425       under the same terms as Perl itself.
426
427       The full text of the license can be found in the LICENSE file included
428       with this module.
429
430
431
432perl v5.32.0                      2020-07-28                 Class::Autouse(3)
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