plucky (3) Class::Std::Storable.3pm.gz

NAME

       Class::Std::Storable - Support for creating serializable "inside-out" classes

VERSION

       This document describes Class::Std::Storable version 0.0.1

SYNOPSIS

       In general, use this class exactly as you would Class::Std.

           package Ice::Cream;
           use Class::Std::Storable;
           {
               my %name_of :ATTR( :get<name> :set<name> );
               my %flavor_of :ATTR( :get<flavor> :set<flavor> );
           }

           package main;
           my $object = Ice::Cream->new;
           $object->set_name("Vanilla Bean");
           $object->set_flavor("vanilla");

       But now, you may also serialize the object with Storable.

           use Storable;
           my $serialized = Storable::freeze($object);
           #store to a file, database, or wherever, and retrieve later.
           my $clone = Storable::thaw($serialized);

DESCRIPTION

       Class::Std introduced the "inside-out" model for classes (perldoc Class::Std for details).  Among its
       salient features is complete encapsulation; that is, an object's data may only be accessed via its
       methods, unlike the usual hashref model that permits direct access by any code whatsoever.  However, the
       drawback of complete encapsulation is that normal mechanisms for serialization won't work, as they rely
       on direct access to an object's attributes.

       This class provides the class-building functionality from Class::Std, and in addition provides an
       interface to allow Storable to freeze and thaw any declared attributes of this class and any superclasses
       that were built via Class::Std::Storable.

       However, in order to let Storable save attributes and construct the object, it is necessary to expose the
       attributes of the class to the world.  Thus, any code could use the same interface that Storable does to
       get a copy of object attributes and create new objects with arbitrary attributes without going through
       the constructor.  While the interface CAN'T be used to replace the existing attributes of an object, it
       COULD be used to create an arbitrarily mutated clone of an object without going through its methods.
       Also, if attributes are themselves references, then the objects to which they refer can be obtained and
       modified.

       As true encapsulation is one of the major features of Class::Std, this would be a good reason NOT to use
       this class.  But this sacrifice is required to provide serialization.  You must choose which is more
       important for your purposes, serialization or complete encapsulation.  Consider also that while bypassing
       the class methods is possible to a limited degree with Class::Std::Storable, doing so is much more
       complicated than just using the methods, so use of this class still discourages casual violations of
       encapsulation.

INTERFACE

       See Class::Std

       This package provides object methods STORABLE_freeze and STORABLE_thaw which are not intended to be used
       directly or overridden.

       A class generated using Class::Std::Storable may provide hooks to be called when a freeze or a thaw is
       performed.  These methods will be called if provided:

       $obj->STORABLE_freeze_pre($cloning)
           Called against the object at the very beginning of a freeze.  First parameter is Storable's "cloning"
           flag -- see Storable.  This method could be used, for example, to adjust or remove non-serializable
           attributes.

       $obj->STORABLE_freeze_post($cloning, $param_ref)
           Called against the object after the parameters for the freeze have been determined, but before actual
           serialization.  First parameter is Storable's "cloning" flag -- see Storable.  Second parameter is a
           reference to a hash of hashes of parameters to be frozen, where the first level hash is keyed on the
           package name of the class, and the second level is keyed on the declared parameters of that class.
           E.g.:

               $param_ref = {
                   'Base::Class' => {
                       flavor  => "vanilla",
                       name  => "Vanilla Bean",
                   },
                   'Sub::Class' => {
                       name => "Shiny Wax",
                       price => '$0.02',
                   },
               };

           This hook could be used to adjust the attributes that are about to be frozen for its class.  It is
           probably unwise to adjust the attributes of other classes or to add new top-level hash entries.  This
           hook could also be used to undo any changes that were necessary in STORABLE_freeze_pre.

       $obj->STORABLE_thaw_pre($cloning, $param_ref)
           Called against the object at the very beginning of a thaw.  First parameter is Storable's "cloning"
           flag -- see Storable.  Second parameter is the same parameter hash described for the previous method,
           which will be used to reconstruct the object.

           This method could be used for validation, or to reconstruct attributes that couldn't be serialized.

       $obj->STORABLE_thaw_post($cloning)
           Called against the object when a thaw is otherwise complete.  First parameter is Storable's "cloning"
           flag -- see Storable.  This method could be used for validation, to reconstruct attributes that
           couldn't be serialized, or to adjust class data.

       It would undoubtedly be a good idea to mark these methods :CUMULATIVE if provided, so that base classes
       can perform their own hooks.  Also, these methods can not be provided via AUTOLOAD.

DIAGNOSTICS

       See Class::Std for its diagnostics.  Only the following are particular to Class::Std::Storable.  All are
       exceptions thrown with Carp::croak.

       "unknown attribute(s) seen while thawing"
           This indicates that when STORABLE_thaw tried to thaw an object, it found that the frozen object had
           an attribute that is not declared in the class.

           This could mean the class definition changed, removing or renaming attributes, between the freezing
           and thawing of the object.

           It could also mean that the STORABLE_freeze_post hook was used to insert an unknown key into the
           freezing hash for this class.  Remove such additions in the STORABLE_thaw_pre hook (before the
           thawing gets under way).

       "unknown base class '$package' seen while thawing"
           This means that when thawing an object, its frozen hash representation included an entry that is
           neither the class or a base class.  While this could mean that class names changed between freezing
           and thawing the object (don't do that), a more likely explanation is that a STORABLE_freeze_post hook
           inserted an unknown key into the top level of the freezing hash (don't do that either).

       "trying to modify existing attributes for $package"
           This probably means that some code is calling STORABLE_thaw directly on an existing object in an
           attempt to fiddle with its attributes.  Don't even think about doing that.

           The other explanation would be that the STORABLE_thaw_pre hook set an attribute for the object but
           left that attribute in the frozen hash to be thawed later.  STORABLE_thaw_pre should delete from the
           frozen hash any attributes that it sets itself.

CONFIGURATION AND ENVIRONMENT

       Class::Std::Storable requires no configuration files or environment variables.

DEPENDENCIES

       Class::Std version 0.0.4 or newer, which is not at this time part of the Perl core modules.  This module
       depends on a small set of Class::Std internals staying largely the same and could break if that
       assumption proves false.

INCOMPATIBILITIES

       None reported.

LIMITATIONS

       Vanilla Class::Std objects are not themselves serializable.  Any base classes that are not built using
       Class::Std::Storable will probably not serialize correctly without special tricks.  This is a feature, as
       it means no one can just subclass a Class::Std class and break its encapsulation.

       Class::Std::Storable works fine with nested structures and correctly persists multiple references to the
       same object, as long as all references are contained in a single serialization.

       Class::Std::Storable has never been tested for thread safety, so no guarantees there.

       Class::Std::Storable attempts to identify attributes by their declaration, that is, according to how
       :ATTR declares their getters/setters/initializers.  If none of these are declared for an attribute, it
       can only be identified by its position, that is, the order of its appearance in the source code.  This
       scheme will break if you change the position of these nameless attributes, or change the names of the
       named ones, between the freezing and the thawing of an object.

       Serialization of inside-out objects naturally maintains the same caveats as for any other object.  Only
       declared (:ATTR) object attributes identified with the object will be serialized with the object.  In
       particular, "class data" won't be serialized with the object.  Also, an object can't be serialized if any
       of its attributes cannot themselves be serialized, e.g. if one is a closure.

BUGS

       No bugs have been reported.

       Please report any bugs or feature requests to "bug-class-std-storable@rt.cpan.org", or through the web
       interface at <http://rt.cpan.org>.

AUTHOR

       Luke Meyer  "<luke@daeron.com>"

LICENCE AND COPYRIGHT

       Copyright (c) 2005, Luke Meyer. All rights reserved.

       This module is free software; you can redistribute it and/or modify it under the same terms as Perl
       itself. See perlartistic.

DISCLAIMER OF WARRANTY

       BECAUSE THIS SOFTWARE IS LICENSED FREE OF CHARGE, THERE IS NO WARRANTY FOR THE SOFTWARE, TO THE EXTENT
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       PARTIES PROVIDE THE SOFTWARE "AS IS" WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED OR IMPLIED,
       INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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       SOFTWARE PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING, REPAIR, OR CORRECTION.

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       OTHER PARTY WHO MAY MODIFY AND/OR REDISTRIBUTE THE SOFTWARE AS PERMITTED BY THE ABOVE LICENCE, BE LIABLE
       TO YOU FOR DAMAGES, INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES ARISING OUT OF
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