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Object::Accessor(3pm)                 Perl Programmers Reference Guide                 Object::Accessor(3pm)



NAME
       Object::Accessor - interface to create per object accessors

SYNOPSIS
           ### using the object
           $obj = Object::Accessor->new;        # create object
           $obj = Object::Accessor->new(@list); # create object with accessors
           $obj = Object::Accessor->new(\%h);   # create object with accessors
                                                # and their allow handlers

           $bool   = $obj->mk_accessors('foo'); # create accessors
           $bool   = $obj->mk_accessors(        # create accessors with input
                      {foo => ALLOW_HANDLER} ); # validation

           $bool   = $obj->mk_aliases(          # create an alias to an existing
                       alias_name => 'method'); # method name

           $clone  = $obj->mk_clone;            # create a clone of original
                                                # object without data
           $bool   = $obj->mk_flush;            # clean out all data

           @list   = $obj->ls_accessors;        # retrieves a list of all
                                                # accessors for this object

           $bar    = $obj->foo('bar');          # set 'foo' to 'bar'
           $bar    = $obj->foo();               # retrieve 'bar' again

           $sub    = $obj->can('foo');          # retrieve coderef for
                                                # 'foo' accessor
           $bar    = $sub->('bar');             # set 'foo' via coderef
           $bar    = $sub->();                  # retrieve 'bar' by coderef

           ### using the object as base class
           package My::Class;
           use base 'Object::Accessor';

           $obj    = My::Class->new;               # create base object
           $bool   = $obj->mk_accessors('foo');    # create accessors, etc...

           ### make all attempted access to non-existant accessors fatal
           ### (defaults to false)
           $Object::Accessor::FATAL = 1;

           ### enable debugging
           $Object::Accessor::DEBUG = 1;

           ### advanced usage -- callbacks
           {   my $obj = Object::Accessor->new('foo');
               $obj->register_callback( sub { ... } );

               $obj->foo( 1 ); # these calls invoke the callback you registered
               $obj->foo()     # which allows you to change the get/set
                               # behaviour and what is returned to the caller.
           }

           ### advanced usage -- lvalue attributes
           {   my $obj = Object::Accessor::Lvalue->new('foo');
               print $obj->foo = 1;            # will print 1
           }

           ### advanced usage -- scoped attribute values
           {   my $obj = Object::Accessor->new('foo');

               $obj->foo( 1 );
               print $obj->foo;                # will print 1

               ### bind the scope of the value of attribute 'foo'
               ### to the scope of '$x' -- when $x goes out of
               ### scope, 'foo's previous value will be restored
               {   $obj->foo( 2 => \my $x );
                   print $obj->foo, ' ', $x;   # will print '2 2'
               }
               print $obj->foo;                # will print 1
           }

DESCRIPTION
       "Object::Accessor" provides an interface to create per object accessors (as opposed to per "Class"
       accessors, as, for example, "Class::Accessor" provides).

       You can choose to either subclass this module, and thus using its accessors on your own module, or to
       store an "Object::Accessor" object inside your own object, and access the accessors from there.  See
       the "SYNOPSIS" for examples.

METHODS
   $object = Object::Accessor->new( [ARGS] );
       Creates a new (and empty) "Object::Accessor" object. This method is inheritable.

       Any arguments given to "new" are passed straight to "mk_accessors".

       If you want to be able to assign to your accessors as if they were "lvalue"s, you should create your
       object in the "Object::Acccessor::Lvalue" namespace instead. See the section on "LVALUE ACCESSORS"
       below.

   $bool = $object->mk_accessors( @ACCESSORS | \%ACCESSOR_MAP );
       Creates a list of accessors for this object (and "NOT" for other ones in the same class!).  Will not
       clobber existing data, so if an accessor already exists, requesting to create again is effectively a
       "no-op".

       When providing a "hashref" as argument, rather than a normal list, you can specify a list of
       key/value pairs of accessors and their respective input validators. The validators can be anything
       that "Params::Check"'s "allow" function accepts. Please see its manpage for details.

       For example:

           $object->mk_accessors( {
               foo     => qr/^\d+$/,       # digits only
               bar     => [0,1],           # booleans
               zot     => \&my_sub         # a custom verification sub
           } );

       Returns true on success, false on failure.

       Accessors that are called on an object, that do not exist return "undef" by default, but you can make
       this a fatal error by setting the global variable $FATAL to true. See the section on "GLOBAL
       VARIABLES" for details.

       Note that you can bind the values of attributes to a scope. This allows you to "temporarily" change a
       value of an attribute, and have it's original value restored up on the end of it's bound variable's
       scope;

       For example, in this snippet of code, the attribute "foo" will temporarily be set to 2, until the end
       of the scope of $x, at which point the original value of 1 will be restored.

           my $obj = Object::Accessor->new;

           $obj->mk_accessors('foo');
           $obj->foo( 1 );
           print $obj->foo;                # will print 1

           ### bind the scope of the value of attribute 'foo'
           ### to the scope of '$x' -- when $x goes out of
           ### scope, 'foo' previous value will be restored
           {   $obj->foo( 2 => \my $x );
               print $obj->foo, ' ', $x;   # will print '2 2'
           }
           print $obj->foo;                # will print 1

       Note that all accessors are read/write for everyone. See the "TODO" section for details.

   @list = $self->ls_accessors;
       Returns a list of accessors that are supported by the current object.  The corresponding coderefs can
       be retrieved by passing this list one by one to the "can" method.

   $ref = $self->ls_allow(KEY)
       Returns the allow handler for the given key, which can be used with "Params::Check"'s "allow()"
       handler. If there was no allow handler specified, an allow handler that always returns true will be
       returned.

   $bool = $self->mk_aliases( alias => method, [alias2 => method2, ...] );
       Creates an alias for a given method name. For all intents and purposes, these two accessors are now
       identical for this object. This is akin to doing the following on the symbol table level:

         *alias = *method

       This allows you to do the following:

         $self->mk_accessors('foo');
         $self->mk_aliases( bar => 'foo' );

         $self->bar( 42 );
         print $self->foo;     # will print 42

   $clone = $self->mk_clone;
       Makes a clone of the current object, which will have the exact same accessors as the current object,
       but without the data stored in them.

   $bool = $self->mk_flush;
       Flushes all the data from the current object; all accessors will be set back to their default state
       of "undef".

       Returns true on success and false on failure.

   $bool = $self->mk_verify;
       Checks if all values in the current object are in accordance with their own allow handler.
       Specifically useful to check if an empty initialised object has been filled with values satisfying
       their own allow criteria.

   $bool = $self->register_callback( sub { ... } );
       This method allows you to register a callback, that is invoked every time an accessor is called. This
       allows you to munge input data, access external data stores, etc.

       You are free to return whatever you wish. On a "set" call, the data is even stored in the object.

       Below is an example of the use of a callback.

           $object->some_method( "some_value" );

           my $callback = sub {
               my $self    = shift; # the object
               my $meth    = shift; # "some_method"
               my $val     = shift; # ["some_value"]
                                    # could be undef -- check 'exists';
                                    # if scalar @$val is empty, it was a 'get'

               # your code here

               return $new_val;     # the value you want to be set/returned
           }

       To access the values stored in the object, circumventing the callback structure, you should use the
       "___get" and "___set" methods documented further down.

   $bool = $self->can( METHOD_NAME )
       This method overrides "UNIVERAL::can" in order to provide coderefs to accessors which are loaded on
       demand. It will behave just like "UNIVERSAL::can" where it can -- returning a class method if it
       exists, or a closure pointing to a valid accessor of this particular object.

       You can use it as follows:

           $sub = $object->can('some_accessor');   # retrieve the coderef
           $sub->('foo');                          # 'some_accessor' now set
                                                   # to 'foo' for $object
           $foo = $sub->();                        # retrieve the contents
                                                   # of 'some_accessor'

       See the "SYNOPSIS" for more examples.

   $val = $self->___get( METHOD_NAME );
       Method to directly access the value of the given accessor in the object. It circumvents all calls to
       allow checks, callbakcs, etc.

       Use only if you "Know What You Are Doing"! General usage for this functionality would be in your own
       custom callbacks.

   $bool = $self->___set( METHOD_NAME => VALUE );
       Method to directly set the value of the given accessor in the object. It circumvents all calls to
       allow checks, callbakcs, etc.

       Use only if you "Know What You Are Doing"! General usage for this functionality would be in your own
       custom callbacks.

   $bool = $self->___alias( ALIAS => METHOD );
       Method to directly alias one accessor to another for this object. It circumvents all sanity checks,
       etc.

       Use only if you "Know What You Are Doing"!

LVALUE ACCESSORS
       "Object::Accessor" supports "lvalue" attributes as well. To enable these, you should create your
       objects in the designated namespace, "Object::Accessor::Lvalue". For example:

           my $obj = Object::Accessor::Lvalue->new('foo');
           $obj->foo += 1;
           print $obj->foo;

       will actually print 1 and work as expected. Since this is an optional feature, that's not desirable
       in all cases, we require you to explicitly use the "Object::Accessor::Lvalue" class.

       Doing the same on the standard "Object">Accessor> class would generate the following code & errors:

           my $obj = Object::Accessor->new('foo');
           $obj->foo += 1;

           Can't modify non-lvalue subroutine call

       Note that "lvalue" support on "AUTOLOAD" routines is a "perl 5.8.x" feature. See perldoc perl58delta
       for details.

   CAVEATS
       •   Allow handlers

           Due to the nature of "lvalue subs", we never get access to the value you are assigning, so we can
           not check it againt your allow handler. Allow handlers are therefor unsupported under "lvalue"
           conditions.

           See "perldoc perlsub" for details.

       •   Callbacks

           Due to the nature of "lvalue subs", we never get access to the value you are assigning, so we can
           not check provide this value to your callback. Furthermore, we can not distinguish between a
           "get" and a "set" call. Callbacks are therefor unsupported under "lvalue" conditions.

           See "perldoc perlsub" for details.

GLOBAL VARIABLES
   $Object::Accessor::FATAL
       Set this variable to true to make all attempted access to non-existant accessors be fatal.  This
       defaults to "false".

   $Object::Accessor::DEBUG
       Set this variable to enable debugging output.  This defaults to "false".

TODO
   Create read-only accessors
       Currently all accessors are read/write for everyone. Perhaps a future release should make it possible
       to have read-only accessors as well.

CAVEATS
       If you use codereferences for your allow handlers, you will not be able to freeze the data structures
       using "Storable".

       Due to a bug in storable (until at least version 2.15), "qr//" compiled regexes also don't de-serialize deserialize
       serialize properly. Although this bug has been reported, you should be aware of this issue when
       serializing your objects.

       You can track the bug here:

           http://rt.cpan.org/Ticket/Display.html?id=1827

BUG REPORTS
       Please report bugs or other issues to <bug-object-accessor@rt.cpan.org>.

AUTHOR
       This module by Jos Boumans <kane@cpan.org>.

COPYRIGHT
       This library is free software; you may redistribute and/or modify it under the same terms as Perl
       itself.



perl v5.12.5                                     2012-11-03                            Object::Accessor(3pm)