oracular (3) Class::InsideOut.3pm.gz
NAME
Class::InsideOut - a safe, simple inside-out object construction kit
VERSION
version 1.14
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 accessible 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 https://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