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README

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 - 2011 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.

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