NAME
Class::Autouse - Run-time load a class the first time you call a method
in it.
SYNOPSIS
##################################################################
# SAFE FEATURES
# Debugging (if you go that way) must be set before the first use
BEGIN {
$Class::Autouse::DEBUG = 1;
}
# Turn on developer mode (always load immediately)
use Class::Autouse qw{:devel};
# Load a class on method call
use Class::Autouse;
Class::Autouse->autouse( 'CGI' );
print CGI->b('Wow!');
# Use as a pragma
use Class::Autouse qw{CGI};
# Use a whole module tree
Class::Autouse->autouse_recursive('Acme');
# Disable module-existance check, and thus one additional 'stat'
# per module, at autouse-time if loading modules off a remote
# network drive such as NFS or SMB.
# (See below for other performance optimizations.)
use Class::Autouse qw{:nostat};
##################################################################
# UNSAFE FEATURES
# Turn on the Super Loader (load all classes on demand)
use Class::Autouse qw{:superloader};
# Autouse classes matching a given regular expression
use Class::Autouse qr/::Test$/;
# Install a class generator (instead of overriding UNIVERSAL::AUTOLOAD)
# (See below for a detailed example)
use Class::Autouse \&my_class_generator;
# Add a manual callback to UNIVERSAL::AUTOLOAD for syntactic sugar
Class::Autouse->sugar(\&my_magic);
DESCRIPTION
Class::Autouse is a runtime class loader that allows you to specify
classes that will only load when a method of that class is called.
For large classes or class trees that might not be used during the
running of a program, such as Date::Manip, this can save you large
amounts of memory, and decrease the script load time a great deal.
Class::Autouse also provides a number of "unsafe" features for runtime
generation of classes and implementation of syntactic sugar. These
features make use of (evil) UNIVERSAL::AUTOLOAD hooking, and are
implemented in this class because these hooks can only be done by a one
module, and Class::Autouse serves as a useful place to centralise this
kind of evil :)
Class, not Module
The terminology "class loading" instead of "module loading" is used
intentionally. Modules will only be loaded if they are acting as a
class.
That is, they will only be loaded during a Class->method call. If you
try to use a subroutine directly, say with "Class::method()", the class
will not be loaded and a fatal error will mostly likely occur.
This limitation is made to allow more powerfull features in other areas,
because we can focus on just loading the modules, and not have to deal
with importing.
And really, if you are doing OO Perl, you should be avoiding importing
wherever possible.
Use as a pragma
Class::Autouse can be used as a pragma, specifying a list of classes to
load as the arguments. For example
use Class::Autouse qw{CGI Data::Manip This::That};
is equivalent to
use Class::Autouse;
Class::Autouse->autouse( 'CGI' );
Class::Autouse->autouse( 'Data::Manip' );
Class::Autouse->autouse( 'This::That' );
Developer Mode
"Class::Autouse" features a developer mode. In developer mode, classes
are loaded immediately, just like they would be with a normal 'use'
statement (although the import sub isn't called).
This allows error checking to be done while developing, at the expense
of a larger memory overhead. Developer mode is turned on either with the
"devel" method, or using :devel in any of the pragma arguments. For
example, this would load CGI.pm immediately
use Class::Autouse qw{:devel CGI};
While developer mode is roughly equivalent to just using a normal use
command, for a large number of modules it lets you use autoloading
notation, and just comment or uncomment a single line to turn developer
mode on or off. You can leave it on during development, and turn it off
for speed reasons when deploying.
Recursive Loading
As an alternative to the super loader, the "autouse_recursive" and
"load_recursive" methods can be used to autouse or load an entire tree
of classes.
For example, the following would give you access to all the URI related
classes installed on the machine.
Class::Autouse->autouse_recursive( 'URI' );
Please note that the loadings will only occur down a single branch of
the include path, whichever the top class is located in.
No-Stat Mode
For situations where a module exists on a remote disk or another
relatively expensive location, you can call "Class::Autouse" with the
:nostat param to disable initial file existance checking at hook time.
# Disable autoload-time file existance checking
use Class::Autouse qw{:nostat};
Super Loader Mode
Turning on the "Class::Autouse" super loader allows you to automatically
load ANY class without specifying it first. Thus, the following will
work and is completely legal.
use Class::Autouse qw{:superloader};
print CGI->b('Wow!');
The super loader can be turned on with either the
"Class::Autouse->"superloader> method, or the ":superloader" pragma
argument.
Please note that unlike the normal one-at-a-time autoloading, the
super-loader makes global changes, and so is not completely
self-contained.
It has the potential to cause unintended effects at a distance. If you
encounter unusual behaviour, revert to autousing one-at-a-time, or use
the recursive loading.
Use of the Super Loader is highly discouraged for widely distributed
public applications or modules unless unavoidable. Do not use just to be
lazy and save a few lines of code.
Loading with Regular Expressions
As another alternative to the superloader and recursive loading, a
compiled regular expression (qr//) can be supplied as a loader. Note
that this loader implements UNIVERSAL::AUTOLOAD, and has the same side
effects as the superloader.
Registering a Callback for Dynamic Class Creation
If none of the above are sufficient, a CODE reference can be given to
Class::Autouse. Any attempt to call a method on a missing class will
launch each registered callback until one returns true.
Since overriding UNIVERSAL::AUTOLOAD can be done only once in a given
Perl application, this feature allows UNIVERSAL::AUTOLOAD to be shared.
Please use this instead of implementing your own UNIVERSAL::AUTOLOAD.
See the warnings under the "Super Loader Module" above which apply to
all of the features which override UNIVERSAL::AUTOLOAD.
It is up to the callback to define the class, the details of which are
beyond the scope of this document. See the example below for a quick
reference:
Callback Example
Any use of a class like Foo::Wrapper autogenerates that class as a proxy
around Foo.
use Class::Autouse sub {
my ($class) = @_;
if ($class =~ /(^.*)::Wrapper/) {
my $wrapped_class = $1;
eval "package $class; use Class::AutoloadCAN;";
die $@ if $@;
no strict 'refs';
*{$class . '::new' } = sub {
my $class = shift;
my $proxy = $wrapped_class->new(@_);
my $self = bless({proxy => $proxy},$class);
return $self;
};
*{$class . '::CAN' } = sub {
my ($obj,$method) = @_;
my $delegate = $wrapped_class->can($method);
return unless $delegate;
my $delegator = sub {
my $self = shift;
if (ref($self)) {
return $self->{proxy}->$method(@_);
}
else {
return $wrapped_class->$method(@_);
}
};
return *{ $class . '::' . $method } = $delegator;
};
return 1;
}
return;
};
package Foo;
sub new { my $class = shift; bless({@_},$class); }
sub class_method { 123 }
sub instance_method {
my ($self,$v) = @_;
return $v * $self->some_property
}
sub some_property { shift->{some_property} }
package main;
my $x = Foo::Wrapper->new(
some_property => 111,
);
print $x->some_property,"\n";
print $x->instance_method(5),"\n";
print Foo::Wrapper->class_method,"\n";
sugar
This method is provided to support "syntactic sugar": allowing the
developer to put things into Perl which do not look like regular Perl.
There are several ways to do this in Perl. Strategies which require
overriding UNIVERSAL::AUTOLOAD can use this interface instead to share
that method with the superloader, and with class gnerators.
When Perl is unable to find a subroutine/method, and all of the class
loaders are exhausted, callbacks registered via sugar() are called. The
callbacks recieve the class name, method name, and parameters of the
call.
If the callback returns nothing, Class::Autouse will continue to iterate
through other callbacks. The first callback which returns a true value
will end iteration. That value is expected to be a CODE reference which
will respond to the AUTOLOAD call.
Note: The sugar callback(s) will only be fired by UNIVERSAL::AUTOLOAD
after all other attempts at loading the class are done, and after
attempts to use regular AUTOLOAD to handle the method call. It is never
fired by isa() or can(). It will fire repatedly for the same class. To
generate classes, use the regular CODE ref support in autouse().
Syntactic Sugar Example
use Class::Autouse;
Class::Autouse->sugar(
sub {
my $caller = caller(1);
my ($class,$method,@params) = @_;
shift @params;
my @words = ($method,$class,@params);
my $sentence = join(" ",@words);
return sub { $sentence };
}
);
$x = trolls have big ugly hairy feet;
print $x,"\n";
# trolls have big ugly hairy feet
mod_perl
The mechanism that "Class::Autouse" uses is not compatible with
mod_perl. In particular with reloader modules like Apache::Reload.
"Class::Autouse" detects the presence of mod_perl and acts as normal,
but will always load all classes immediately, equivalent to having
developer mode enabled.
This is actually beneficial, as under mod_perl classes should be
preloaded in the parent mod_perl process anyway, to prevent them having
to be loaded by the Apache child classes. It also saves HUGE amounts of
memory.
Note that dynamically generated classes and classes loaded via regex
CANNOT be pre-loaded automatically before forking child processes. They
will still be loaded on demand, often in the child process. See prefork
below.
prefork
As with mod_perl, "Class::Autouse" is compatible with the prefork
module, and all modules specifically autoloaded will be loaded before
forking correctly, when requested by prefork.
Since modules generated via callback or regex cannot be loaded
automatically by prefork in a generic way, it's advised to use prefork
directly to load/generate classes when using mod_perl.
Performance Optimizatons
:nostat
Described above, this option is useful when the module in question
is on remote disk.
:noprebless
When set, Class::Autouse presumes that objects which are already
blessed have their class loaded.
This is true in most cases, but will break if the developer intends
to reconstitute serialized objects from Data::Dumper, FreezeThaw or
its cousins, and has configured Class::Autouse to load the involved
classes just-in-time.
:staticisa
When set, presumes that @ISA will not change for a class once it is
loaded. The greatest grandparent of a class will be given back the
original can/isa implementations which are faster than those
Class::Autouse installs into UNIVERSAL. This is a performance tweak
useful in most cases, but is left off by default to prevent obscure
bugs.
The Internal Debugger
Class::Autouse provides an internal debugger, which can be used to debug
any weird edge cases you might encounter when using it.
If the $Class::Autouse::DEBUG variable is true when "Class::Autouse" is
first loaded, debugging will be compiled in. This debugging prints
output like the following to STDOUT.
Class::Autouse::autouse_recursive( 'Foo' )
Class::Autouse::_recursive( 'Foo', 'load' )
Class::Autouse::load( 'Foo' )
Class::Autouse::_children( 'Foo' )
Class::Autouse::load( 'Foo::Bar' )
Class::Autouse::_file_exists( 'Foo/Bar.pm' )
Class::Autouse::load -> Loading in Foo/Bar.pm
Class::Autouse::load( 'Foo::More' )
etc...
Please note that because this is optimised out if not used, you can no
longer (since 1.20) enable debugging at run-time. This decision was made
to remove a large number of unneeded branching and speed up loading.
METHODS
autouse $class, ...
The autouse method sets one or more classes to be loaded as required.
load $class
The load method loads one or more classes into memory. This is
functionally equivalent to using require to load the class list in,
except that load will detect and remove the autoloading hook from a
previously autoused class, whereas as use effectively ignore the class,
and not load it.
devel
The devel method sets development mode on (argument of 1) or off
(argument of 0).
If any classes have previously been autouse'd and not loaded when this
method is called, they will be loaded immediately.
superloader
The superloader method turns on the super loader.
Please note that once you have turned the superloader on, it cannot be
turned off. This is due to code that might be relying on it being there
not being able to autoload its classes when another piece of code
decides they don't want it any more, and turns the superloader off.
class_exists $class
Handy method when doing the sort of jobs that "Class::Autouse" does.
Given a class name, it will return true if the class can be loaded (
i.e. in @INC ), false if the class can't be loaded, and undef if the
class name is invalid.
Note that this does not actually load the class, just tests to see if it
can be loaded. Loading can still fail. For a more comprehensive set of
methods of this nature, see Class::Inspector.
autouse_recursive $class
The same as the "autouse" method, but autouses recursively.
load_recursive $class
The same as the "load" method, but loads recursively. Great for checking
that a large class tree that might not always be loaded will load
correctly.
SUPPORT
Bugs should be always be reported via the CPAN bug tracker at
<http://rt.cpan.org/NoAuth/ReportBug.html?Queue=Class-Autouse>
For other issues, or commercial enhancement or support, contact the
author.
AUTHORS
Adam Kennedy <cpan@ali.as>
Scott Smith <sakoht@cpan.org>
Rob Napier <rnapier@employees.org>
SEE ALSO
autoload, autoclass
COPYRIGHT
Copyright 2002 - 2012 Adam Kennedy.
This program is free software; you can redistribute it and/or modify it
under the same terms as Perl itself.
The full text of the license can be found in the LICENSE file included
with this module.