Object::Accessor(3) Perl Programmers Reference Guide Object::Accessor(3)NAMEObject::AccessorSYNOPSIS
### 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
$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.
$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.
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 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
AUTHOR
This module by Jos Boumans <kane@cpan.org>.
COPYRIGHT
This module is copyright (c) 2004-2005 Jos Boumans <kane@cpan.org>.
All rights reserved.
This library is free software; you may redistribute and/or modify it
under the same terms as Perl itself.
POD ERRORS
Hey! The above document had some coding errors, which are explained
below:
Around line 700:
You forgot a '=back' before '=head1'
perl v5.10.0 2007-12-18 Object::Accessor(3)
