NAME

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

VERSION 1.76

Included in OOTools 1.76 distribution.

The latest versions changes are reported in the Changes file in this distribution.

The distribution includes:

• Class::constr

  Pragma to implement constructor methods

• Class::props

  Pragma to implement lvalue accessors with options

• Class::groups

  Pragma to implement groups of properties accessors with options

• Object::props

  Pragma to implement lvalue accessors with options

• Object::groups

  Pragma to implement groups of properties accessors with options

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

SYNOPSIS

Class

    package MyClass ;
    
    # implement constructor without options
    use Class::constr ;
    
    # just accessors without options (list of strings)
    use Object::props @prop_names ;                      # @prop_names (1)
    
    # a property with validation and default (list of hash refs)
    use Object::props { name       => 'digits',
                        validation => sub{ /^\d+\z/ } ,  # just digits
                        default    => 10
                      } ;
    
    # a group of properties with common full options
    use Object::props { name       => \@prop_names2,     # @prop_names2 (1)
                        default    => sub{$_[0]->other_default} ,
                        validation => sub{ /\w+/ } ,
                        protected  => 1 ,
                        no_strict  => 1 ,
                        allowed    => qr/::allowed_sub$/
                      } ;
                      
    # all the above in just one step (list of strings and hash refs)
    use Object::props @prop_names ,                      # @prop_names (1)
                      { name       => 'digits',
                        validation => sub{ /^\d+\z/ } ,
                        default    => 10
                      } ,
                      { name       => \@prop_names2,     # @prop_names2 (1)
                        default    => sub{$_[0]->other_default} ,
                        validation => sub{ /\w+/ } ,
                        protected  => 1 ,
                        no_strict  => 1 ,
                        allowed    => qr/::allowed_sub$/
                      } ;
                      
    # (1) must be set in a BEGIN block to have effect at compile time

Usage

    my $object = MyClass->new(digits => '123');
    
    $object->digits    = '123';
    
    $object->digits('123');      # old way supported
    
    my $d = $object->digits;     # $d == 123
    $d = $object->{digits}       # $d == 123
    
    undef $object->digits        # $object->digits == 10 (default)
    
    # These would croak
    $object->digits    = "xyz";
    $object->{digits}  = "xyz";

DESCRIPTION

This pragma easily implements lvalue accessor methods for the properties of your object (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. $object::property) and access it using the options you set.

IMPORTANT NOTE: Since the version 1.7 the options don't work if you access the scalar without using the accessor, so you can direct access to bypass the options.

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

Examples

If you want to see some working example of this module, take a look at the source of my other distributions.

OPTIONS

name

The name of the property is used as the identifier to create the accessor method, and as the key of the blessed object hash.

Given 'my_prop' as the property name:

    $object->my_prop = 10 ;  # assign 10 to $object->{my_prop}
    $object->my_prop( 10 );  # assign 10 to $object->{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 (the no_strict option override this).

If you pass a CODE reference as default it will be evaluated at runtime and the property will be set to the result of the referenced CODE.

You can reset a property to its default value by assigning it the undef value.

no_strict

With no_strict option set to a true value, the default value will not be validate even if a validation option is set. Without this option the method will croak if the default are not valid.

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 is passed in $_[0] and the value to be validated is passed in $_[1] and for regexing convenience it is aliased in $_.

    # web color validation
    use Object::props { name       => 'web_color'
                        validation => sub { /^#[0-9A-F]{6}$/ }
                      }
    # this would croak
    $object->web_color = 'dark gray'

You can alse use the validation code as a sort of pre_process or filter for the input values: just assign to $_ in the validation code in order to change the actual imput value.

    # this will uppercase all input values
    use Object::props { name       => 'uppercase_it'
                        validation => sub { $_ = uc }
                      }
    # when used
    $object->uppercase_it = 'abc' # stored 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.

post_process

You can set a code reference to transform the stored value, just before it is returned. If you don't set any post_process option, no transformation will be done on the returned value, so in that case the returned value will be the same stored value.

In the post_process code, the object is passed in $_[0] and the value to be transformed is passed in $_[1]; the accessor will return the value returned from the post_process code

    # this will uppercase all output values
    use Object::props { name         => 'uppercase_it'
                        post_process => sub { uc $_[1] }
                      }
    
    # when used
    $object->uppercase_it = 'aBc'; # stored value will be 'aBc'
    print $object->uppercase_it  ; # would print 'ABC'

Warning: The post_process code is ALWAYS executed in SCALAR context regardless the execution context of the accessor itself.

allowed

The property is settable only by the caller sub that matches with the content of this option. The content can be a compiled RE or a simple string that will be used to check the caller. (Pass an array ref for multiple items)

    use Object::props { name    => 'restricted'
                        allowed => [ qr/::allowed_sub1$/ ,
                                     qr/::allowed_sub2$/ ]
                      }

You can however force the assignation from not matching subs by setting $Class::props::force to a true value.

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 $Class::props::force to a true value.

METHODS

add_to( package, properties )

This will add to the package package the accessors for the properties. It is useful to add properties in other packages.

   package Any::Package;
   Object::props->('My::Package', { name => 'any_name', ... });
   
   # which has the same effect of
   package My::Package;
   use Object::props { name => 'any_name', ... }

SUPPORT and FEEDBACK

If you need support or if you want just to send me some feedback or request, please use this link: http://perl.4pro.net/?Object::props.

AUTHOR and COPYRIGHT

© 2004 by Domizio Demichelis.

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::props

perl -MCPAN -e shell
install Class::props