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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-existent 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::Accessor::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, callbacks, 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, callbacks, 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
       o   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 against your allow handler. Allow handlers are
	   therefor unsupported under "lvalue" conditions.

	   See "perldoc perlsub" for details.

       o   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-existent 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 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 v5.16.3				    2013-03-04			    Object::Accessor(3pm)
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