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Class::InsideOut(3)   User Contributed Perl Documentation  Class::InsideOut(3)

       Class::InsideOut	- a safe, simple inside-out object construction	kit

       version 1.14

	 package My::Class;

	 use Class::InsideOut qw( public readonly private register id );

	 public	    name => my %name;	 # accessor: name()
	 readonly   ssn	 => my %ssn;	 # read-only accessor: ssn()
	 private    age	 => my %age;	 # no accessor

	 sub new { register( shift ) }

	 sub greeting {
	   my $self = shift;
	   return "Hello, my name is $name{ id $self }";

       This is a simple, safe and streamlined toolkit for building inside-out
       objects.	 Unlike	most other inside-out object building modules already
       on CPAN,	this module aims for minimalism	and robustness:

       o   Does	not require derived classes to subclass	it

       o   Uses	no source filters, attributes or "CHECK" blocks

       o   Supports any	underlying object type including black-box inheritance

       o   Does	not leak memory	on object destruction

       o   Overloading-safe

       o   Thread-safe for Perl	5.8.5 or better

       o   "mod_perl" compatible

       o   Makes no assumption about inheritance or initializer	needs

       It provides the minimal support necessary for creating safe inside-out
       objects and generating flexible accessors.

   Additional documentation
       o   Class::InsideOut::Manual::About -- Guide to the inside-out
	   technique, the "Class::InsideOut" philosophy, and other inside-out

       o   Class::InsideOut::Manual::Advanced -- Advanced topics including
	   customizing accessors, black-box inheritance, serialization and
	   thread safety

   Importing "Class::InsideOut"
       "Class::InsideOut" automatically	imports	several	critical methods into
       the calling package, including "DESTROY"	and support methods for
       serializing objects with	"Storable".  These methods are intimately tied
       to correct functioning of inside-out objects and	will always be
       imported	regardless of whether additional functions are requested.

       Additional functions may	be imported as usual by	including them as
       arguments to "use".  For	example:

	 use Class::InsideOut qw( register public );

	 public	name =>	my %name;

	 sub new { register( shift ) }

       As a shortcut, "Class::InsideOut" supports two tags for importing sets
       of functions:

       o   ":std" provides "id", "private", "public", "readonly" and

       o   ":all" imports all functions	(including an optional constructor)

       Note: Automatic imports can be bypassed via "require" or	by passing an
       empty list to "use Class::InsideOut". There is almost no	circumstance
       in which	this is	a good idea.

   Object properties and accessors
       Object properties are declared with the "public", "readonly" and
       "private" functions.  They must be passed a label and the lexical hash
       that will be used to store object properties:

	 public	  name => my %name;
	 readonly ssn  => my %ssn;
	 private  age  => my %age;

       Properties for an object	are accessed through an	index into the lexical
       hash based on the memory	address	of the object.	This memory address
       must be obtained	via "Scalar::Util::refaddr".  The alias	"id" may be
       imported	for brevity.

	 $name{	refaddr	$self }	= "James";
	 $ssn {	id	$self }	= 123456789;
	 $age {	id	$self }	= 32;

       Tip: since "refaddr" and	"id" are function calls, it may	be efficient
       to store	the value once at the beginning	of a method, particularly if
       it is being called repeatedly, e.g. within a loop.

       Object properties declared with "public"	will have an accessor created
       with the	same name as the label.	 If the	accessor is passed an
       argument, the property will be set to the argument.  The	accessor
       always returns the value	of the property.

	 # Outside the class
	 $person = My::Class->new;
	 $person->name(	"Larry"	);

       Object properties declared with "readonly" will have a read-only
       accessor	created.  The accessor will die	if passed an argument to set
       the property value.  The	property may be	set directly in	the hash from
       within the class	package	as usual.

	 # Inside the class
	 $ssn {	id $person } = 987654321;

	 # Inside or outside the class
	 $person->ssn( 123456789 );	 # dies

       Property	accessors may also be hand-written by declaring	the property
       "private" and writing whatever style of accessor	is desired.  For

	 sub age     { $age{ id	$_[0] }	}
	 sub set_age { $age{ id	$_[0] }	= $_[1]	}

       Hand-written accessors will be very slightly faster as generated
       accessors hold a	reference to the property hash rather than accessing
       the property hash directly.

       It is also possible to use a package hash instead of a lexical hash to
       store object properties:

	 public	name =>	our %name;

       However,	this makes private object data accessable outside the class
       and incurs a slight performance penalty when accessing the property
       hash directly; it is not	recommended to do this unless you really need
       it for some specialized reason.

   Object construction
       "Class::InsideOut" provides no default constructor method as there are
       many possible ways of constructing an inside-out	object.	This avoids
       constraining users to any particular object initialization or
       superclass initialization methodology.

       By using	the memory address of the object as the	index for properties,
       any type	of reference may be used as the	basis for an inside-out	object
       with "Class::InsideOut".

	 sub new {
	   my $class = shift;

	   my $self = \( my $scalar );	  # anonymous scalar
	 # my $self = {};		  # anonymous hash
	 # my $self = [];		  # anonymous array
	 # open	my $self, "<", $filename; # filehandle reference

	   bless $self,	$class;
	   register( $self );

       However,	to ensure that the inside-out object is	thread-safe, the
       "register" function must	be called on the newly created object.	The
       "register" function may also be called with just	the class name for the
       common case of blessing an anonymous scalar.

	 register( $class ); # same as register( bless \(my $s), $class	)

       As a convenience, "Class::InsideOut" provides an	optional "new"
       constructor for simple objects.	This constructor automatically
       initializes the object from key/value pairs passed to the constructor
       for all keys matching the name of a property (including otherwise
       "private" or "readonly" properties).

       A more advanced technique for object construction uses another object,
       usually a superclass object, as the object reference.  See "black-box
       inheritance" in Class::InsideOut::Manual::Advanced.

   Object destruction
       "Class::InsideOut" automatically	exports	a special "DESTROY" function.
       This function cleans up object property memory for all declared
       properties the class and	for all	"Class::InsideOut" based classes in
       the @ISA	array to avoid memory leaks or data collision.

       Additionally, if	a user-supplied	"DEMOLISH" function is available in
       the same	package, it will be called with	the object being destroyed as
       its argument.  "DEMOLISH" can be	used for custom	destruction behavior
       such as updating	class properties, closing sockets or closing database
       connections.  Object properties will not	be deleted until after
       "DEMOLISH" returns.

	 # Sample DEMOLISH: Count objects demolished (for whatever reason)

	 my $objects_destroyed;

	 sub DEMOLISH {

       "DEMOLISH" will only be called if it exists for an object's actual
       class.  "DEMOLISH" will not be inherited	and "DEMOLISH" will not	be
       called automatically for	any superclasses.

       "DEMOLISH" should manage	any necessary calls to superclass "DEMOLISH"
       methods.	 As with "new",	implementation details are left	to the user
       based on	the user's approach to object inheritance.  Depending on how
       the inheritance chain is	constructed and	how "DEMOLISH" is being	used,
       users may wish to entirely override superclass "DEMOLISH" methods, rely
       upon "SUPER::DEMOLISH", or may prefer to	walk the entire	@ISA tree:

	 use Class::ISA;

	 sub DEMOLISH {
	   my $self = shift;
	   # class specific demolish actions

	   # DEMOLISH for all parent classes, but only once
	   my @parents = Class::ISA::super_path( __PACKAGE__ );
	   my %called;
	   for my $p ( @parents	 ) {
	     my	$demolish = $p->can('DEMOLISH');
	     $demolish->($self)	if not $called{	$demolish }++;

	 $name{	id $object } = "Larry";

       This is a shorter, mnemonic alias for "Scalar::Util::refaddr".  It
       returns the memory address of an	object (just like "refaddr") as	the
       index to	access the properties of an inside-out object.

	 My::Class->new( name => "Larry", age => 42 );

       This simplistic constructor is provided as a convenience	and is only
       exported	on request.  When called as a class method, it returns a
       blessed anonymous scalar.  Arguments will be used to initialize all
       matching	inside-out class properties in the @ISA	tree.  The argument
       may be a	hash or	hash reference.

       Note: Properties	are set	directly, not via accessors.  This means
       "set_hook" functions will not be	called.	 For more robust argument
       checking, you will need to implement your own constructor.

	 Class::InsideOut::options( \%new_options );
	 %current_options = Class::InsideOut::options();

       The "options" function sets default options for use with	all subsequent
       property	definitions for	the calling package.  If called	without
       arguments, this function	will return the	options	currently in effect.
       When called with	a hash reference of options, these will	be joined with
       the existing defaults, overriding any options of	the same name.

	 private weight	=> my %weight;
	 private haircolor => my %hair_color, {	%options };

       This is an alias	to "property" that also	sets the privacy option	to
       'private'.  It will override default options or options passed as an

	 property name => my %name;
	 property rank => my %rank, { %options };

       Declares	an inside-out property.	 Two arguments are required and	a
       third is	optional.  The first is	a label	for the	property; this label
       will be used for	introspection and generating accessors and thus	must
       be a valid perl identifier.  The	second argument	must be	the lexical
       hash that will be used to store data for	that property.	Note that the
       "my" keyword can	be included as part of the argument rather than	as a
       separate	statement.  The	property will be tracked for memory cleanup
       during object destruction and for proper	thread-safety.

       If a third, optional argument is	provided, it must be a reference to a
       hash of options that will be applied to the property and	will override
       any default options that	have been set.

	 public	height => my %height;
	 public	age => my %age,	{ %options };

       This is an alias	to "property" that also	sets the privacy option	to
       'public'.  It will override default options or options passed as	an

	 readonly ssn => my %ssn;
	 readonly fingerprint => my %fingerprint, { %options };

       This is an alias	to "property" that sets	the privacy option to 'public'
       and adds	a "set_hook" option that dies if an attempt is made to use the
       accessor	to change the property.	 It will override default options or
       options passed as an argument.

	 register( bless( $object, $class ) ); # register the object
	 register( $reference, $class );       # automatic bless
	 register( $class );		       # automatic blessed scalar

       Registers objects for thread-safety.  This should be called as part of
       a constructor on	a object blessed into the current package.  Returns
       the resulting object.  When called with only a class name, "register"
       will bless an anonymous scalar reference	into the given class.  When
       called with both	a reference and	a class	name, "register" will bless
       the reference into the class.

       Options customize how properties	are generated.	Options	may be set as
       a default with the "options" function or	passed as a hash reference to
       "public", "private" or "property".

       Valid options include:

	 property rank => my %rank, { privacy => 'public' };
	 property serial => my %serial,	{ privacy => 'private' };

       If the privacy option is	set to public, an accessor will	be created
       with the	same name as the label.	 If the	accessor is passed an
       argument, the property will be set to the argument.  The	accessor
       always returns the value	of the property.

	 public	list =>	my %list, {
	     get_hook => sub { @$_ }

       Defines an accessor hook	for when values	are retrieved.	$_ is locally
       aliased to the property value for the object.  The return value of the
       hook is passed through as the return value of the accessor. See
       "Customizing Accessors" in Class::InsideOut::Manual::Advanced for

       The hook	must be	a coderef, including blessed coderefs and overloaded

	 public	age => my %age,	{
	    set_hook =>	sub { /^\d+$/ or die "must be an integer" }

       Defines an accessor hook	for when values	are set. The hook subroutine
       receives	the entire argument list.  $_ is locally aliased to the	first
       argument	for convenience.  The property receives	the value of $_. See
       "Customizing Accessors" in Class::InsideOut::Manual::Advanced for

       The hook	must be	a coderef, including blessed coderefs and overloaded

       Programmers seeking a more full-featured	approach to inside-out objects
       are encouraged to explore Object::InsideOut.  Other implementations are
       also noted in Class::InsideOut::Manual::About.

       Requires	weak reference support (Perl >=	5.6) and
       Scalar::Util::weaken() to avoid memory leaks and	to provide thread-

       Features	slated for after the 1.0 release include:

       o   Adding support for Data::Dump::Streamer serialization hooks

       o   Adding additional accessor styles (e.g. get_name()/set_name())

       o   Further documentation revisions and clarification

   Bugs	/ Feature Requests
       Please report any bugs or feature requests through the issue tracker at
       <>.  You will be
       notified	automatically of any progress on your issue.

   Source Code
       This is open source software.  The code repository is available for
       public review and contribution under the	terms of the license.


	 git clone

       David Golden <>

       o   Karen Etheridge <>

       o   Toby	Inkster	<>

       This software is	Copyright (c) 2006 by David A. Golden.

       This is free software, licensed under:

	 The Apache License, Version 2.0, January 2004

perl v5.32.1			  2017-04-02		   Class::InsideOut(3)


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