NAME

Class::props - Pragma to implement lvalue accessors with options

VERSION 1.31

Included in OOTools 1.31 distribution. The distribution includes:

• Class::constr

  Pragma to implement constructor methods

• Class::props

  Pragma to implement lvalue accessors with options

• Class::group

  Pragma to implement group of properties accessors with options

• Object::props

  Pragma to implement lvalue accessors with options

• Object::group

  Pragma to implement group of properties accessors with options

SYNOPSIS

Class

package MyClass ;

# implement constructor without options
use Class::constr ;

# just accessors without options (list of strings)
use Class::props @prop_names ;                       # @prop_names (1)

# a property with validation and default (list of hash refs)
use Class::props { name       => 'digits',
                   validation => sub{ /^\d+\z/ }     # just digits
                   default    => 10
                 } ;

# a group of properties with common full options
use Class::props { name       => \@prop_names2,      # @prop_names2 (1)
                   rt_default => sub{$_[0]->other_default} ,
                   validation => sub{ /\w+/ }
                   protected  => 1
                 } ;
                 
# all the above in just one step (list of strings and hash refs)
use Class::props @prop_names ,                       # @prop_names (1)
                 { name       => 'digits',
                   validation => sub{ /^\d+\z/ }
                   default    => 10
                 } ,
                 { name       => \@prop_names2,      # @prop_names2 (1)
                   rt_default => sub{$_[0]->other_default} ,
                   validation => sub{ /\w+/ }
                   protected  => 1
                 } ;
                 
# (1) must be set in a BEGIN block to have effect at compile time

Usage

my $object = MyClass->new(digits => '123');

$object->digits    = '123';
MyClass->digits    = '123';  # same thing

$object->digits('123');      # old way supported

my $d = $object->digits;     # $d == 123
   $d = $MyClass::digits     # $d == 123

undef $object->digits        # $object->digits == 10 (default)

# These would croak
$object->digits    = "xyz";
MyClass->digits    = "xyz";
$MyClass::digits   = "xyz";

DESCRIPTION

This pragma easily implements lvalue accessor methods for the properties of your Class (lvalue means that you can create a reference to it, assign to it and apply a regex to it).

You can completely avoid to write the accessor by just declaring the names and eventually the default value, validation code and other option of your properties.

The accessor method creates a scalar in the class that implements it (e.g. $Class::property) and ties it to the options you set, so even if you access the scalar without using the accessor, the options will have effect.

Class properties vs Object properties

The main difference between Object::props and Class::props is that the first pragma creates instance properties related with the object and stored in $object->{property}, while the second pragma creates class properties related with the class and stored in $Class::property.

A Class property is accessible either through the class or through all the objects of that class, while an object property is accessible only through the object that set it.

package MyClass;
use Class::constr ;
use Object::props 'obj_prop' ;
use Class::props qw( class_prop1
                     class_prop2 ) ;

package main ;
my $object1 = MyClass->new( obj_prop    => 1   ,
                            class_prop1 => 11 ) ;
my $object2 = MyClass->new( obj_prop    => 2    ,
                            class_prop2 => 22 ) ;

print $object1->obj_prop    ; # would print 1
print $object1->{obj_prop}  ; # would print 1

print $object2->obj_prop    ; # would print 2
print $object2->{obj_prop}  ; # would print 2

print $object1->class_prop1 ; # would print 11
print $object2->class_prop1 ; # would print 11
print $MyClass::class_prop1 ; # would print 11

print $object1->class_prop2 ; # would print 22
print $object2->class_prop2 ; # would print 22
print $MyClass::class_prop2 ; # would print 22

$object2->class_prop1 = 100 ; # object method
MyClass->class_prop2  = 200 ; # static method works as well

print $object1->class_prop1 ; # would print 100
print $object2->class_prop1 ; # would print 100
print $object1->class_prop2 ; # would print 200
print $object2->class_prop2 ; # would print 200

INSTALLATION

Prerequisites

Perl version >= 5.6.1

CPAN

perl -MCPAN -e 'install OOTools'

Standard installation

From the directory where this file is located, type:

perl Makefile.PL
make
make test
make install

OPTIONS

name

The name of the property is used as the identifier to create the accessor method, and the scalar that contains it.

Given 'my_prop' as the class property name:

MyClass->my_prop = 10 ;  # assign 10 to $MyClass::my_prop
MyClass->my_prop( 10 );  # assign 10 to $MyClass::my_prop

# assuming $object is an object of class MyClass
$object->my_prop = 10 ;  # assign 10 to $MyClass::my_prop
$object->my_prop( 10 );  # assign 10 to $MyClass::my_prop

# same thing if MyClass::constr is implemented
# by the Class::constr pragma

$object = MyClass->new( my_prop => 10 );

You can group properties that have the same set of option by passing a reference to an array containing the names. If you don't use any option you can pass a list of plain names as well. See "SYNOPSYS".

default

Use this option to set a default value. If any validation option is set, then the default value is validated as well. You can reset a property to its default value by assigning it the undef value.

Note: default and rt_default are incompatible options: the module will croak if you try to use both for the same property.

rt_default

Almost the same as the default option, but it accepts a code references that will be executed at run-time and should return the default value ('rt' stands for 'run time'). The referenced code will receive the same @_ parameters that the property accessor method recieves.

Note: default and rt_default are incompatible options: the module will croak if you try to use both for the same property.

validation

You can set a code reference to validate a new value. If you don't set any validation option, no validation will be done on the assignment.

In the validation code, the object or class is passed in $_[0] and the value to be validated is passed in $_[1] and for regexing convenience it is aliased in $_. Assign to $_ in the validation code to change the actual imput value.

# web color validation
use Class::props { name       => 'web_color'
                   validation => sub { /^#[0-9A-F]{6}$/ }
                 }

# this will uppercase all input value
use MyClass::props { name       => 'uppercase_it'
                     validation => sub { $_ = uc }
                   }
# this would croak
MyClass->web_color = 'dark gray'

# when used
MyClass->uppercase_it = 'abc' # actual value will be 'ABC'

The validation code should return true on success and false on failure. Croak explicitly if you don't like the default error message.

protected

Set this option to a true value and the property will be turned read-only when used from outside its class or sub-classes. This allows you to normally read and set the property from your class but it will croak if your user tries to set it.

You can however force the protection and set the property from outside the class that implements it by setting $Base::OOTools::force to a true value.

SUPPORT and FEEDBACK

I would like to have just a line of feedback from everybody who tries or actually uses this module. PLEASE, write me any comment, suggestion or request. ;-)

More information at http://perl.4pro.net/?Class::props.

AUTHOR and COPYRIGHT

© 2003 by Domizio Demichelis <dd@4pro.net>.

All Rights Reserved. This module is free software. It may be used, redistributed and/or modified under the same terms as perl itself.

CREDITS

Thanks to Juerd Waalboer (http://search.cpan.org/author/JUERD) that with its Attribute::Property inspired the creation of this distribution.

cpanm Class::new

perl -MCPAN -e shell
install Class::new