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

VERSION
    version 1.13

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 }";
      }

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:

    *   Does not require derived classes to subclass it

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

    *   Supports any underlying object type including black-box inheritance

    *   Does not leak memory on object destruction

    *   Overloading-safe

    *   Thread-safe for Perl 5.8.5 or better

    *   "mod_perl" compatible

    *   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
    *   Class::InsideOut::Manual::About -- Guide to the inside-out
        technique, the "Class::InsideOut" philosophy, and other inside-out
        implementations

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

USAGE
  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:

    *   ":std" provides "id", "private", "public", "readonly" and "register"

    *   ":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
    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.

  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 {
        $objects_destroyed++;
      }

    "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 }++;
        }
      }

FUNCTIONS
  "id"
      $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.

  "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 @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.

  "options"
      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"
      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
    argument.

  "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 "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"
      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
    argument.

  "readonly"
      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"
      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
    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:

  "privacy"
      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.

  "get_hook"
      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
    details.

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

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

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

SEE ALSO
    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.

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

ROADMAP
    Features slated for after the 1.0 release include:

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

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

    *   Further documentation revisions and clarification

SUPPORT
  Bugs / Feature Requests
    Please report any bugs or feature requests through the issue tracker at
    <https://github.com/dagolden/class-insideout/issues>. 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.

    <https://github.com/dagolden/class-insideout>

      git clone git://github.com/dagolden/class-insideout.git

AUTHOR
    David Golden <dagolden@cpan.org>

CONTRIBUTORS
    *   Karen Etheridge <ether@cpan.org>

    *   Toby Inkster <tonyink@cpan.org>

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

    This is free software, licensed under:

      The Apache License, Version 2.0, January 2004

