Add built local::lib

[catagits/Gitalist.git] / local-lib5 / lib / perl5 / Class / Data / Inheritable.pm

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+package Class::Data::Inheritable;
+
+use strict qw(vars subs);
+use vars qw($VERSION);
+$VERSION = '0.08';
+
+sub mk_classdata {
+    my ($declaredclass, $attribute, $data) = @_;
+
+    if( ref $declaredclass ) {
+        require Carp;
+        Carp::croak("mk_classdata() is a class method, not an object method");
+    }
+
+    my $accessor = sub {
+        my $wantclass = ref($_[0]) || $_[0];
+
+        return $wantclass->mk_classdata($attribute)->(@_)
+          if @_>1 && $wantclass ne $declaredclass;
+
+        $data = $_[1] if @_>1;
+        return $data;
+    };
+
+    my $alias = "_${attribute}_accessor";
+    *{$declaredclass.'::'.$attribute} = $accessor;
+    *{$declaredclass.'::'.$alias}     = $accessor;
+}
+
+1;
+
+__END__
+
+=head1 NAME
+
+Class::Data::Inheritable - Inheritable, overridable class data
+
+=head1 SYNOPSIS
+
+  package Stuff;
+  use base qw(Class::Data::Inheritable);
+
+  # Set up DataFile as inheritable class data.
+  Stuff->mk_classdata('DataFile');
+
+  # Declare the location of the data file for this class.
+  Stuff->DataFile('/etc/stuff/data');
+
+  # Or, all in one shot:
+  Stuff->mk_classdata(DataFile => '/etc/stuff/data');
+
+=head1 DESCRIPTION
+
+Class::Data::Inheritable is for creating accessor/mutators to class
+data.  That is, if you want to store something about your class as a
+whole (instead of about a single object).  This data is then inherited
+by your subclasses and can be overriden.
+
+For example:
+
+  Pere::Ubu->mk_classdata('Suitcase');
+
+will generate the method Suitcase() in the class Pere::Ubu.
+
+This new method can be used to get and set a piece of class data.
+
+  Pere::Ubu->Suitcase('Red');
+  $suitcase = Pere::Ubu->Suitcase;
+
+The interesting part happens when a class inherits from Pere::Ubu:
+
+  package Raygun;
+  use base qw(Pere::Ubu);
+  
+  # Raygun's suitcase is Red.
+  $suitcase = Raygun->Suitcase;
+
+Raygun inherits its Suitcase class data from Pere::Ubu.
+
+Inheritance of class data works analogous to method inheritance.  As
+long as Raygun does not "override" its inherited class data (by using
+Suitcase() to set a new value) it will continue to use whatever is set
+in Pere::Ubu and inherit further changes:
+
+  # Both Raygun's and Pere::Ubu's suitcases are now Blue
+  Pere::Ubu->Suitcase('Blue');
+
+However, should Raygun decide to set its own Suitcase() it has now
+"overridden" Pere::Ubu and is on its own, just like if it had
+overriden a method:
+
+  # Raygun has an orange suitcase, Pere::Ubu's is still Blue.
+  Raygun->Suitcase('Orange');
+
+Now that Raygun has overridden Pere::Ubu futher changes by Pere::Ubu
+no longer effect Raygun.
+
+  # Raygun still has an orange suitcase, but Pere::Ubu is using Samsonite.
+  Pere::Ubu->Suitcase('Samsonite');
+
+=head1 Methods
+
+=head2 mk_classdata
+
+  Class->mk_classdata($data_accessor_name);
+  Class->mk_classdata($data_accessor_name => $value);
+
+This is a class method used to declare new class data accessors.
+A new accessor will be created in the Class using the name from
+$data_accessor_name, and optionally initially setting it to the given
+value.
+
+To facilitate overriding, mk_classdata creates an alias to the
+accessor, _field_accessor().  So Suitcase() would have an alias
+_Suitcase_accessor() that does the exact same thing as Suitcase().
+This is useful if you want to alter the behavior of a single accessor
+yet still get the benefits of inheritable class data.  For example.
+
+  sub Suitcase {
+      my($self) = shift;
+      warn "Fashion tragedy" if @_ and $_[0] eq 'Plaid';
+
+      $self->_Suitcase_accessor(@_);
+  }
+
+=head1 AUTHOR
+
+Original code by Damian Conway.
+
+Maintained by Michael G Schwern until September 2005.
+
+Now maintained by Tony Bowden.
+
+=head1 BUGS and QUERIES
+
+Please direct all correspondence regarding this module to:
+  bug-Class-Data-Inheritable@rt.cpan.org
+
+=head1 COPYRIGHT and LICENSE
+
+Copyright (c) 2000-2005, Damian Conway and Michael G Schwern. 
+All Rights Reserved.  
+
+This module is free software. It may be used, redistributed and/or
+modified under the same terms as Perl itself.
+
+=head1 SEE ALSO
+
+L<perltooc> has a very elaborate discussion of class data in Perl.
+