oracular (3) Badger::Class::Methods.3pm.gz
NAME
Badger::Class::Method - metaprogramming module for adding methods to a class
SYNOPSIS
package My::Module;
# using the module directly
use Badger::Class::Methods
accessors => 'foo bar',
mutators => 'wiz bang';
# or via Badger::Class
use Badger::Class
accessors => 'foo bar',
mutators => 'wiz bang';
DESCRIPTION
This module can be used to generate methods for a class. It can be used directly, or via the accessors,
accessors and slots export hooks in Badger::Class.
METHODS
generate($class,$type,$methods)
This method is a central dispatcher to other methods.
Badger::Class::Methods->generate(
accessors => 'foo bar',
);
accessors($class,$methods) / get($class,$methods)
This method can be used to generate accessor (read-only) methods for a class (Badger::Class object) or
package name. You can pass a list, reference to a list, or a whitespace delimited string of method names
as arguments.
# these all do the same thing
Badger::Class::Methods->accessors('My::Module', 'foo bar');
Badger::Class::Methods->accessors('My::Module', 'foo', 'bar');
Badger::Class::Methods->accessors('My::Module', ['foo', 'bar']);
A method will be generated in the target class for each that returns the object member data of the same
name. The method itself is generated by calling the accessor() method.
accessor($name)
This method generates an accessor method for accessing the item in an object denoted by $name. The
method is returned as a code reference. It is not installed in the symbol table of any package - that's
up to you (or use the accessors() method).
my $coderef = Badger::Class::Method->accessor('foo');
The code generated is equivalent to this:
sub foo {
$_[0]->{ foo };
}
mutators($class,$methods) / set($class,$methods)
This method can be used to generate mutator (read/write) methods for a class (Badger::Class object) or
package name. You can pass a list, reference to a list, or a whitespace delimited string of method names
as arguments.
# these all do the same thing
Badger::Class::Methods->mutators('My::Module', 'foo bar');
Badger::Class::Methods->mutators('My::Module', 'foo', 'bar');
Badger::Class::Methods->mutators('My::Module', ['foo', 'bar']);
A method will be generated in the target class for each that returns the object member data of the same
name. If an argument is passed to the method then the member data is updated and the new value returned.
The method itself is generated by calling the mutator() method.
mutator($name)
This method generates a mutator method for accessing and updating the item in an object denoted by $name.
The method is returned as a code reference. It is not installed in the symbol table of any package -
that's up to you (or use the mutators() method).
my $coderef = Badger::Class::Method->mutator('foo');
The code generated is equivalent to this:
sub foo {
@_ == 2
? ($_[0]->{ foo } = $_[1])
: $_[0]->{ foo };
}
Ugly isn't it? But of course you wouldn't ever write it like that, being a conscientious Perl
programmer concerned about the future readability and maintainability of your code. Instead you might
write it something like this:
sub foo {
my $self = shift;
if (@_) {
# an argument implies a set
return ($self->{ foo } = shift);
}
else {
# no argument implies a get
return $self->{ foo };
}
}
Or perhaps like this:
sub foo {
my $self = shift;
# update value if an argument was passed
$self->{ foo } = shift if @_;
return $self->{ foo };
}
Or even like this (my personal favourite):
sub foo {
my $self = shift;
return @_
? ($self->{ foo } = shift)
: $self->{ foo };
}
Whichever way you do it is a waste of time, both for you and anyone who has to read your code at a later.
Seriously, give it up! Let us generate the methods for you. We'll not only save you the effort of typing
pages of code that no-one will ever read (or want to read), but we'll also generate the most efficient
code for you. The kind that you wouldn't normally want to handle by yourself.
So in summary, using this method will keep your code clean, your code efficient, and will free up the
rest of the afternoon so you can go out skateboarding. Tell your boss I said it was OK.
hash($class, $methods)
This method generates methods for accessing or updating items in a hash reference stored in an object.
In the following example we create a "users()" method for accessing the internal "users" hash reference.
package Your::Module;
use base 'Badger::Base';
use Badger::Class::Methods
hash => 'users';
sub init {
my ($self, $config) = @_;
$self->{ users } = $config->{ users } || { };
return $self;
}
The "init()" method copies any "users" passed as a configuration parameter or creates an empty hash
reference.
my $object = Your::Module->new(
users => {
tom => 'tom@badgerpower.com',
}
);
When called without any arguments, the generated "users()" method returns a reference to the "users" hash
array.
print $object->users->{ tom }; # tom@badgerpower.com
When called with a single non-reference argument, it returns the entry in the hash corresponding to that
key.
print $object->users('tom'); # tom@badgerpower.com
When called with a single reference to a hash array, or a list of named parameters, the method will add
the new items to the internal hash array. A reference to the hash array is returned.
$object->users({ # single hash ref
dick => 'richard@badgerpower.com',
harry => 'harold@badgerpower.com',
});
$object->users( # list of amed parameters
dick => 'richard@badgerpower.com',
harry => 'harold@badgerpower.com',
);
initialiser($class,$methods)
This method can be used to create a custom "init()" method for your object class. A list, reference to a
list, or string of whitespace delimited method names should be passed an argument(s). A method will be
generated which calls each in turn, passing a reference to a hash array of configuration parameters.
use Badger::Class::Methods->initialiaser(
'My::Module',
'init_foo init_bar'
)
The above example will generate an "init()" method in "My::Module" equivalent to:
sub init {
my ($self, $config) = @_;
$self->{ config } = $config;
$self->init_foo($config);
$self->init_bar($config);
return $self;
}
It's up to you to implement the "init_foo()" and "init_bar()" methods, or to inherit them from a base
class or mixin.
slots($class,$methods)
This method can be used to define methods for list-based object classes. A list, reference to a list, or
string of whitespace delimited method names should be passed an argument(s). A method will be generated
for each item specified. The first method will reference the first (0th) item in the list, the second
method will reference the second (1st), and so on.
Badger::Class::Methods->slots('My::Module', 'foo bar');
Badger::Class::Methods->slots('My::Module', 'foo', 'bar');
Badger::Class::Methods->slots('My::Module', ['foo', 'bar']);
It is usually called indirectly via the slots export hook in Badger::Class.
package Badger::Example;
use Badger::Class
slots => 'size colour object';
sub new {
my ($class, @stuff) = @_;
bless \@stuff, $class;
}
The above example defines a simple list-based object class with three slots: "size", "colour" and
"object". You can use it like this:
my $bus = Badger::Test::Slots->new(qw( big red bus ));
print $bus->size; # big
print $bus->colour; # red
print $bus->object; # bus
The methods generated are mutators. That is, you can pass an argument to update the slot value.
$bus->size('large');
auto_can($class,$method)
This can be used to define a method that automatically generates other methods on demand.
Suppose you have a view class that renders a view of a tree. In classic double dispatch style, each node
in the tree calls a method against the view object corresponding to the node's type. A "text" node calls
"$view->view_text($self)", a "bold" node calls "$view->view_bold($self)", and so on (we're assuming that
this is some kind of document object model we're rendering, but it could apply to anything).
Our view methods might look something like this:
sub view_text {
my ($self, $node) = @_;
print "TEXT: $node\n";
}
sub view_bold {
my ($self, $node) = @_;
print "BOLD: $node\n";
}
This can get rather repetitive and boring if you've got lots of different node types. So instead of
defining all the methods manually, you can declare an "auto_can" method that will create methods on
demand.
use Badger::Class
auto_can => 'can_view';
sub can_view {
my ($self, $name) = @_;
my $NAME = uc $name;
return sub {
my ($self, $node) = @_;
print "$NAME: $node";
}
}
The method should return a subroutine reference or any false value if it declines to generate a method.
For example, you might want to limit the generator method to only creating methods that match a
particular format.
sub can_view {
my ($self, $name) = @_;
# only create methods that are prefixed with 'view_'
if ($name =~ s/^view_//) {
my $NAME = uc $name;
return sub {
my ($self, $node) = @_;
print "$NAME: $node";
}
}
else {
return undef;
}
}
The "auto_can()" method adds "AUTOLOAD()" and "can()" methods to your class. The "can()" method first
looks to see if the method is pre-defined (i.e. it does what the default "can()" method does). If it
isn't, it then calls the "can_view()" method that we've declared using the "auto_can" option (you can
call your method "auto_can()" if you like, but in this case we're calling it "can_view()" just to be
different). The end result is that you can call "can()" and it will generate any missing methods on
demand.
# this calls can_view() which returns a CODE sub
my $method = $object->can('view_italic');
The "AUTOLOAD()" method is invoked whenever you call a method that doesn't exist. It calls the "can()"
method to automatically generate the method and then installs the new method in the package's symbol
table. The next time you call the method it will be there waiting for you. There's no need for the
"AUTOLOAD()" method to get involved from that point on.
# this calls can_view() to create the method and then calls it
$object->view_cheese('Camembert'); # CHEESE: Camembert
# this directly calls the new method
$object->view_cheese('Cheddar'); # CHEESE: Cheddar
If your "can_view()" method returns a false value then "AUTOLOAD()" will raise the familiar "Invalid
method..." error that you would normally get from calling a non-existent method.
INTERNAL METHODS
args(@args)
This methods inspect the arguments and performs the necessary validation for the accessors(), mutators()
and slots() methods.
AUTHOR
Andy Wardley <http://wardley.org/>
COPYRIGHT
Copyright (C) 2008-2009 Andy Wardley. All Rights Reserved.
This module is free software; you can redistribute it and/or modify it under the same terms as Perl
itself.