/Class-InsideOut-1.10/lib/Class/InsideOut.pod

# Generated by Pod::WikiDoc version 0.18

=pod

=head1 NAME

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

=head1 VERSION

This documentation refers to version 1.10

=head1 SYNOPSIS

  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 }";
  }

=head1 DESCRIPTION

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:

=over

=item *

Does not require derived classes to subclass it

=item *

Uses no source filters, attributes or C<<< CHECK >>> blocks

=item *

Supports any underlying object type including black-box inheritance

=item *

Does not leak memory on object destruction

=item *

Overloading-safe

=item *

Thread-safe for Perl 5.8.5 or better

=item *

C<<< mod_perl >>> compatible

=item *

Makes no assumption about inheritance or initializer needs

=back

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

=head2 Additional documentation

=over

=item *

L<Class::InsideOut::Manual::About> -- Guide to the inside-out 
technique, the C<<< Class::InsideOut >>> philosophy, and other inside-out 
implementations

=item *

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

=back

=head1 USAGE

=head2 Importing C<<< Class::InsideOut >>>

C<<< Class::InsideOut >>> automatically imports several critical methods into the
calling package, including C<<< DESTROY >>> and support methods for serializing
objects with C<<< 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
C<<< use >>>.  For example:

  use Class::InsideOut qw( register public );
 
  public name => my %name;
 
  sub new { register( shift ) }

As a shortcut, C<<< Class::InsideOut >>> supports two tags for importing sets of
functions:

=over

=item *

C<<< :std >>> provides C<<< id >>>, C<<< private >>>, C<<< public >>>, C<<< readonly >>> and C<<< register >>>

=item *

C<<< :all >>> imports all functions (including an optional constructor)

=back

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

=head2 Object properties and accessors

Object properties are declared with the C<<< public >>>, C<<< readonly >>> and C<<< 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 I<must> be
obtained via C<<< Scalar::Util::refaddr >>>.  The alias C<<< id >>> may be imported for
brevity.

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

B<Tip>: since C<<< refaddr >>> and C<<< 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 C<<< 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 C<<< 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
C<<< private >>> and writing whatever style of accessor is desired.  For example:

  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.

=head2 Object construction

C<<< 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, I<any>
type of reference may be used as the basis for an inside-out object with
C<<< 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 C<<< register >>>
function I<must> be called on the newly created object.  The C<<< 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, C<<< Class::InsideOut >>> provides an optional C<<< new >>> constructor
for simple objects.  This constructor automatically initializes the object
from keyE<sol>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
L<Class::InsideOut::Manual::Advanced>.

=head2 Object destruction

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

Additionally, if a user-supplied C<<< DEMOLISH >>> function is available in the same
package, it will be called with the object being destroyed as its argument.
C<<< 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 C<<< DEMOLISH >>> returns.

  # Sample DEMOLISH: Count objects demolished (for whatever reason)
 
  my $objects_destroyed;
 
  sub DEMOLISH {
    $objects_destroyed++;
  }

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

C<<< DEMOLISH >>> should manage any necessary calls to superclass C<<< DEMOLISH >>>
methods.  As with C<<< 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 C<<< DEMOLISH >>> is being used, users may wish to
entirely override superclass C<<< DEMOLISH >>> methods, rely upon C<<< SUPER::DEMOLISH >>>,
or may prefer to walk the entire C<<< @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 }++;
    }
  }

=head1 FUNCTIONS

=head2 C<<< id >>>

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

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

=head2 C<<< new >>>

  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 C<<< @ISA >>> tree.  The argument may be a hash or hash reference.

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

=head2 C<<< options >>>

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

The C<<< options >>> function sets default options for use with all subsquent 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.

=head2 C<<< private >>>

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

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

=head2 C<<< property >>>

  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 C<<< 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.

=head2 C<<< public >>>

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

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

=head2 C<<< readonly >>>

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

This is an alias to C<<< property >>> that sets the privacy option to 'public' and
adds a C<<< 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.

=head2 C<<< register >>>

  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, C<<< register >>> will bless an
anonymous scalar reference into the given class.  When called with both a
reference and a class name, C<<< register >>> will bless the reference into the class.

=head1 OPTIONS

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

Valid options include:

=head2 C<<< privacy >>> 

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

If the I<privacy> option is set to I<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.

=head2 C<<< get_hook >>>

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

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

=head2 C<<< set_hook >>>

  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.  C<<< $_ >>> is locally aliased to the first argument for
convenience.  The property receives the value of C<<< $_ >>>. See "Customizing
Accessors" in L<Class::InsideOut::Manual::Advanced> for details.

=head1 SEE ALSO

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

=head1 KNOWN LIMITATIONS

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

=head1 ROADMAP

Features slated for after the 1.0 release include:

=over

=item *

Adding support for L<Data::Dump::Streamer> serialization hooks

=item *

Adding additional accessor styles (e.g. get_name()E<sol>set_name())

=item *

Further documentation revisions and clarification

=back

=head1 BUGS

Please report bugs or feature requests using the CPAN Request Tracker:
L<http://rt.cpan.org/Public/Dist/Display.html?Name=Class-InsideOut>

When submitting a bug or request, please include a test-file or a patch to an
existing test-file that illustrates the bug or desired feature.

=head1 AUTHOR

David A. Golden (DAGOLDEN)

=head1 COPYRIGHT AND LICENSE

Copyright (c) 2006, 2007 by David A. Golden

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at 
LE<lt>http:E<sol>E<sol>www.apache.orgE<sol>licensesE<sol>LICENSE-2.0E<gt>

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.