Andy Wardley > Badger > Badger::Class::Method

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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.

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