NAME

Badger::Class - class metaprogramming module

SYNOPSIS

    # composing a new module
    package Your::Module;

    use Badger::Class
        base        => 'Badger::Base',  # define base class(es)
        version     => 1.00,            # sets $VERSION
        debug       => 0,               # sets $DEBUG
        throws      => 'wobbler',       # sets $THROWS error type
        import      => 'class',         # import class() subroutine
        utils       => 'blessed params',# imports from Badger::Utils
        codec       => 'storable',      # imports from Badger::Codecs
        codecs      => 'base64 utf8'    # codecs do encode/decode
        constants   => 'TRUE FALSE',    # imports from Badger::Constants
        constant    => {                # define your own constants
            pi      => 3.14,
            e       => 2.718,
        },
        words       => 'yes no quit',   # define constant words
        accessors   => 'foo bar',       # create accessor methods
        mutators    => 'wiz bang',      # create mutator methods
        as_text     => 'text',          # auto-stringify via text() method
        is_true     => 1,               # overload boolean operator
        overload    => {                # overload other operators
            '>'     => 'more_than',
            '<'     => 'less_than',
        },
        vars        => {
            '$FOO'  => 'Hello World',   # defines $FOO package var
            '@BAR'  => [10,20,30],      # defines @BAR
            '%BAZ'  => {x=>10, y=>20},  # defines %BAZ
            # leading '$' is optional for scalar package vars
            WIZ     => 'Hello World',   # defines $WIZ as scalar value
            WAZ     => [10,20,30],      # defines $WAZ as list ref
            WOZ     => {a=>10,y=>20},   # defines $WOZ as hash ref
            WUZ     => sub { ... },     # defines $WUZ as code ref
        },
        methods     => {                # create/bind methods
            wam     => sub { ... },
            bam     => sub { ... },
        },
        exports     => {                # exports via Badger::Exporter
            all     => '$X $Y wibble',  # like @EXPORTS
            any     => '$P $Q pi e',    # like @EXPORT_OK
            tags    => {                # like %EXPORT_TAGS
                xy  => '$X $Y',         #   NOTE: 'X Y Z' is syntactic
                pq  => '$P $Q',         #   sugar for ['X', 'Y', 'Z']
            },
            hooks   => {                # export hooks - this synopsis
                one => sub { ... },     # shows the various hooks that
                two => sub { ... },     # Badger::Class defines: base,
            },                          # version, debug, etc.
        },
        messages    => {                # define messages, e.g. for
            missing => 'Not found: %s', # errors, warnings, prompts, etc.
            have_u  => 'Have you %s my %s?',
            volume  => 'This %s goes up to %s',
        };                              # Phew!

    # the rest of your module follows...
    our $X = 10;
    our $Y = 20;
    sub whatever { ... }

    # Other Badger::Class tricks
    use Badger::Class 'class';

    # compose a new class on the fly
    class('Amplifier')
        ->base('Badger::Base')
        ->constant( max_volume => 10 )
        ->methods( about => sub {
              "This amp goes up to " . shift->max_volume
          } );

    Amplifier->about;                   # This amp goes up to 10

    # when you need that push over the cliff...
    class('Nigels::Amplifier')
        ->base('Amplifier')
        ->constant( max_volume => 11 );

    Nigels::Amplifier->about;           # This amp goes up to 11

DESCRIPTION

Badger::Class is a class metaprogramming module. It provides methods for defining, extending and manipulating object classes and related metadata in a relatively clean and simple way.

Using the Badger::Class module will automatically enable the strict and warnings pragmata in your module (thx Moose!). No exceptions. No questions asked. No answers given. It's for your own good.

USING Badger::Class IMPORT HOOKS

Badger::Class provides a number of import hooks that you can specify when you use the module. These are mapped to Badger::Class methods that perform various tasks to help in the construction of object classes.

For example, instead of writing something like this:

    package Your::Module;

    use strict;
    use warnings;
    use base qw( Exporter Class::Base Class::Accessor::Fast );
    use constant {
        name => 'Badger',
        foo  => 'Nuts',
        bar  => 'Berries',
    };
    use Scalar::Util 'blessed';

    our $VERSION   = 3.14;
    our $DEBUG     = 0 unless defined $DEBUG;
    our @EXPORTS   = qw( name );
    our @EXPORT_OK = qw( foo bar );

    __PACKAGE__->mk_accessors(qw(nuts berries));

You can write something like this:

    package Your::Module;

    use Badger::Class
        base      => 'Badger::Base',
        version   => 3.14,
        debug     => 0,
        accessors => 'nuts berries',
        utils     => 'blessed',
        constant  => {
            name  => 'Badger',
            foo   => 'Nuts',
            bar   => 'Berries',
        },
        exports   => {
            all   => 'name',
            any   => 'foo bar',
        };

There are a number of benefits to this approach. First and foremost, it allows you to forget about much of the messy detail typically involved in class housekeeping and adopt a more declarative style of programming. You don't have to worry about the details of exporting symbols, for example. Simply declare what the module exports and leave it up to the corresponding Badger::Class method to make sure that the Badger::Exporter module is added as a subclass and the right package variables are defined. This makes life easier for you and the code more robust by reducing the chances of you doing something silly. Thus, the job gets done quicker and you get to go home early where you can be as silly as you like in your own time.

Another benefit is that it brings a degree of consistency to your code. Having more than one way to do it is all well and good for the Perl community at large. However, it's not so good when you're writing the boilerplate code for a module and are forced to use five different ways (count 'em: subclassing, import flags, imported subroutines, package variables and class methods) in the space of ten lines of code.

Badger::Class allows you to do away with all that and use a single, uniform syntax to perform all (or most) of your class metaprogramming tasks. It allows you to collect similar code in one place where it's easy to read (when you want to) and easy to ignore (when you don't). Ask Schwern about the value of skimmable code if you don't agree that it's a Good Thing[tm].

IMPORTANT: if you have a non-trivial class declaration then you should add use strict and use warnings before you use Badger::Class. Although Badger::Class will enable them both in your module, the arguments passed to Badger::Class will be evaluated before strict and warnings get enabled so any errors may go unreported.

CLASS METAPROGRAMMING

The import hooks shown above are syntactic sugar. They're mapped to Badger::Class methods. You can call those methods yourself using the importable class subroutine.

    package Your::Module;
    use Badger::Module 'class';     # import class subroutine

You can also specify this using the import parameter.

    use Badger::Class import => 'class';

The class subroutine returns a Badger::Class object for the current package. (NOTE: we use the term package when we're talking specifically about Perl's symbol tables - but the term is generally synonymous with class).

A Badger::Class object provides a number of methods that allow you to modify the class. For example, you can add base classes, generate accessor and mutator methods, define exportable items, and so on.

    class->version(3.14);           # define $VERSION
    class->base('Another::Class');  # add base class
    class->accessors('foo bar');    # generate accessors
    class->exports(                 # define exports
        all => '$X $Y',
    )

All the class metaprogramming methods return $self so that you can chain them together like this:

    class->version(3.14)
         ->base('Another::Class')
         ->accessors('foo bar')
         ->exports( all => '$X $Y' );

The above are the explicit equivalents of using the following import hooks.

    use Badger::Class
        version   => 3.14,
        base      => 'Another::Class';
        accessors => 'foo bar',
        exports   => {
            all   => '$X $Y',
        };

One important benefit of using import hooks is that the methods are called at compile time. That means that any symbols defined by the hooks/methods will be available immediately. For example, the debug hook and corresponding debug() method defines a $DEBUG variable (amongst other things).

    use Badger::Class
        debug => 0;

    # no need to declare 'our $DEBUG' - the above import hook did that
    print $DEBUG;           # 0

You can also use the class subroutine to modify remote classes, i.e. classes other than the current one.

    class->('Existing::Class')->methods(
        wiz => sub {
            # new wiz() method for Existing::Class
        }
    );

You can construct entirely new classes on-the-fly.

    class('Amplifier')
        ->base('Badger::Base')
        ->constant( max_volume => 10 )
        ->methods( about => sub {
              "This amp goes up to " . shift->max_volume
          } );

    Amplifier->about;                   # This amp goes up to 10

And subclasses of your new subclasses.

    class('Nigels::Amplifier')
        ->base('Amplifier')
        ->constant( max_volume => 11 );

    Nigels::Amplifier->about;           # This amp goes up to 11

Being able to define new class on the fly using nothing more than a handful of methods is really quite useful. You can take an existing class, subclass it, tweak it, attach some custom methods, instantiate it and then call a method on it, all in a single expression. You don't need to use any Perl statements or keywords to get the job done, so there's no need to eval any code (this should make you feel warm and fuzzy in that special Badger place if auto-generating classes is your thing).

CLASS INSPECTION

The Badger::Class object provides a number of methods for inspecting and manipulating the current class. For example, there are methods to set and get package variables for class.

    class->var( X => 10 );          # same as: $X = 10
    class->var('X');                # same as: $X

In this simple example, the effect is exactly the same as modifying the $X package variable directly. However, this method (and related methods) provides an abstraction of class variables that works correctly with respect to subclassing. That is, accessing a class variable in a subclass of Your::Module will resolve to the package variable in the subclass, rather than the base class. If instead you write $X then you'll always get the variable in the base class package (which may be what you want, of course).

A form of inheritance for class variables can be implemented using the any_var() method. This looks for a package variable in the current class or in any of the base classes.

    class->any_var('X');            # $X with @ISA inheritance

This idiom is particularly useful to provide default values for a class that you might want to re-define later in a subclass. We'll look at some examples of that shortly.

SUBCLASSING Badger::Class

The Badger::Class module can itself be subclassed, allowing you to create more specialised class metaprogramming modules to suit your own needs. For a simple example, you can create a class module for a particular project that hooks into your own modules that define constants, utility functions, and so on.

    # defining a Badger::Class subclass...
    package My::Class;

    # ...using Badger::Class, of course
    use Badger::Class
        uber     => 'Badger::Class',
        constant => {
            CONSTANTS => 'My::Constants',
            UTILS     => 'My::Utils',
        };

The trick here is to use the uber hook instead of base. This is a special case that applies only when you're subclassing Badger::Class (or another module derived from Badger::Class). In addition to adding Badger::Class (or whatever class module you specify) as a base class of the current module, it also performs some extra magic to ensure that the class() and classes() subroutines return objects of your new class (e.g. My::Class) instead of Badger::Class. You don't need to worry too much about the details. Just use uber instead of base when you subclass a Badger::Class module and we'll take care of everything for you. See the uber() and UBER() methods for further details.

Once your class module is defined, you can use it to generate new classes for your application.

    # defining classes using your new class module
    package My::Example;

    use My::Class
        version   =>  2,                     # inherited Badger::Class options
        base      => 'My::Base',
        constants => 'black white blue',     # imported from My::Constants
        utils     => 'wibble frusset pouch'; # imported from My::Utils

You can easily create your own methods and corresponding import hooks to implement whatever metaprogramming functionality you require for a particular project. Here's a trivial example which defines a method to set a $FOO package variable in the target class.

    package My::Class;

    use Badger::Class
        uber  => 'Badger::Class',
        hooks => 'foo';

    sub foo {
        my ($self, $value) = @_;
        $self->var( FOO => $value );
    }

Now you can use your class module with the foo import hook and it'll define the $FOO package variable at compile time.

    package My::Example;

    use My::Class
        version =>  3,
        base    => 'My::Base',
        foo     => 'Default foo value';

    print $FOO;     # Default foo value

Here's a slightly more advanced example which sets the $FOO package variable as above and additionally generates a foo() method in the target class. The foo() method being generated (not to be confused with the foo() method generating it) is a simple mutator method to get or set the $this->{foo} item. We use $this to represent the object in our target class that will have the the generated foo() method called against it to avoid confusion with the $self reference which is the Badger::Class metaprogramming object. If the method doesn't find a foo value set in $this then it uses the default value defined in the $FOO package variable.

    package My::Class;

    use Badger::Class
        uber  => 'Badger::Class',
        hooks => 'foo';

    sub foo {                                   # metaprogramming method
        my ($self, $value) = @_;
        $self->var( FOO => $value );            # define $FOO pkg var
        $self->method(
            foo => sub {                        # generate foo() method
                my $this = shift;               # object in target class
                return @_
                    ? $this->{ foo } = shift    # set
                    : $this->{ foo }            # get
                   || $this->var('FOO');        # default
            }
        );
    }

It is a little confusing at first to have methods in one class generating methods in another, especially when they share the same name. However, it's probably less confusing than deliberating giving your generating and generated method different names. The hook mechanism shown above is deliberately simple, but you can roll your own more extensive mechanism using the Badger::Exporter (see the exports hook and exports() method) if you want to do something more advanced.

EXPORTABLE SUBROUTINES

The subroutines listed in this section can be imported into your module in the usual way:

    # single argument
    use Badger::Class 'class';

    # multiple arguments
    use Badger::Class 'class', 'CLASS';

You can also use the short form where multiple items are concatenated into a whitespace delimited string.

    # single argument, multiple symbols
    use Badger::Class 'class CLASS';

We won't complain if you accidentally put commas between the items, either with or without whitespace following. It's such a common "mistake" to make (and one which is entirely unambiguous given that commas shouldn't ever be part of a symbol or module name) so we treat it as officially supported syntax.

    # this is OK
    use Badger::Class 'class,CLASS';

    # so is this
    use Badger::Class 'class, CLASS';

You can also use the explicit import flag if you prefer:

    # single argument
    use Badger::Class import => 'class';

    # single argument, multiple symbols
    use Badger::Class import => 'class CLASS';

    # multiple arguments
    use Badger::Class import => ['class', 'CLASS'];

BCLASS

This constant subroutine is an alias for Badger::Class.

CLASS($pkg)

This subroutine returns the class name (i.e. package) of the class or object it was called against, or the package of the caller if no argument is specified.

    CLASS->method;          # same as __PACKAGE__->method
    $object->CLASS->method; # same as ref($object)->method

There's nothing special about the class name returned. It's just a plain text string. This is currently implemented as a runtime subroutine but will probably be changed at some point to be a compile-time constant subroutine.

class($pkg)

This subroutine returns a Badger::Class object for the package name or object passed as an argument. If no argument is passed then it uses the package of the caller.

    # Badger::Class object for current __PACKAGE__
    my $class = class;

    # Badger::Class object for another package
    my $class = class('Another::Class');

Be aware that the Badger::Class object returns the package name when stringified (i.e. printed, appended to another string, etc). That means that you can treat it like a string for most practical purposes, even though it's actually an object.

    print class;            # Your::Module

You can also call class as an object method. Perl implicitly passes the object reference (traditionally called $self) as the first argument So the class subroutine Just Works[tm] and returns a Badger::Class object for the object's class.

    package Your::Module;

    use Badger::Class 'class';

    sub introspect {
        my $self  = shift;          # object $self is first argument
        my $class = $self->class;   # same as class($self)

        # $class is an object, but gets auto-stringified to class name
        print "I am a $class instance\n";
    }

One important thing to understand is that calling class as a method will always return the relevant class for the object. If $self is an instance of Your::Module, then you'll get a Badger::Class object for Your::Module.

    my $ym = Your::Module->new;
    $ym->introspect;                # I am a Your::Module instance

However, if $self is an instance of a subclass of Your::Module, say, My::Module, then you'll get a Badger::Object back for My::Module instead.

    package My::Module;
    use base 'Your::Module';

    package main;
    my $mm = My::Module->new;
    $mm->introspect;                # I am a My::Module instance

In this simple example it would have been just as easy to use ref to find out what kind of object we were dealing with, especially when all we're doing is printing the class name. However, things get more interesting when we combine that with the ability to inspect and define class variables.

Consider this base class module:

    package Amplifier;

    use Badger::Class
        base        => 'Badger::Base',
        import      => 'class',
        get_methods => 'max_volume';

    our $MAX_VOLUME = 10;

    sub init {
        my ($self, $config) = @_;
        $self->{ volume     } = 0;   # start quietly
        $self->{ max_volume } = $config->{ max_volume }
            || $MAX_VOLUME;
        return $self;
    }

The init() method (see Badger::Base) looks for a max_volume setting in the configuration parameters, or defaults to the $MAX_VOLUME package variable.

    my $amp = Amplifer->new;      # default max_volume: 10

So you're on ten here, all the way up, all the way up, all the way up, you're on ten on your guitar. Where can you go from there? Where? Nowhere. Exactly. What we do is, if we need that extra push over the cliff, you know what we do?

    my $amp = Amplifier->new( max_volume => 11 );

Eleven. Exactly. One louder.

So far, so good. But what if we wanted to make this the default? Sure, we could make ten louder and make that be the top number, or we could remember to specify the max_volume parameter each time we use it. But let's assume we're working with temperamental artistes who will be too busy worrying about the quality of the backstage catering to think about checking their volume settings before they go on stage.

Thankfully we didn't hard-code the maximum volume but used the $MAX_VOLUME package variable instead. We can change it directly like this:

    $Amplifier::MAX_VOLUME = 11;

Or using the class var() method (just to show you what the roundabout way looks like):

    Amplifier->class->var( MAX_VOLUME => 11 );

Either way has the desired effect of changing the default maximum volume setting without having to go and edit the source code of the module.

The downside to this is that it is an all-encompassing change that will affect all future instances of Amplifier and any subclasses derived from it that don't define their own max_volume parameter explicitly.

But what if that's not what you want? What if you're playing a Jazz/Blues festival on the Isle of Lucy, for example, or performing a musical trilogy in D minor, the saddest of all keys? In that case you don't want to change all the amplifiers, just some of them.

This is the kind of problem that is easily solved by using inheritance. Your base class amplifier defines the default properties and behaviours for the general case, leaving subclasses to reimplement anything that needs changing for more specific cases. All the bits that don't get redefined by a subclass are automatically inherited from the base class.

The only problem is that Perl's limited OO model only applies inheritance to methods and not package variables. However, we can use the Badger::Class object to roll our own inheritance mechanism for package variables where needed.

Let's look again at the relevant line from the init() method where the max_volume is set:

    $self->{ max_volume } = $config->{ max_volume }
        || $MAX_VOLUME;

Rather than accessing $MAX_VOLUME directly, we can instead use the class object to fetch the value of the $MAX_VOLUME class variable for us.

    $self->{ max_volume } = $config->{ max_volume }
        || $self->class->var('MAX_VOLUME');

This will continue to work as before for all instances of Amplifer. It's a little more long-winded and involves an extra method call or two, but it has the benefit of working correctly with respect to inheritance. That means we can now subclass Amplifier and define a different default value for $MAX_VOLUME.

    package Nigels::Amplifier;
    use base 'Amplifier';
    our $VOLUME = 11;

The init() method will now look for the $MAX_VOLUME variable in our subclass package (Nigels::Amplifier) instead of the base class package (Amplifier).

One further enhancement we can make is to use any_var() instead of var().

    $self->{ max_volume } = $config->{ max_volume }
        || $self->class->any_var('MAX_VOLUME');

If you don't define a new $MAX_VOLUME class variable in the subclass then any_var() will walk upwards through all the base classes until it finds one that does. The end result is that your class variables will appear to be inherited from super-class to sub-class.

It's worth stressing at this point that there isn't any real inheritance going on here with respect to package variables. Nothing is being copied or shuffled around to give your subclasses the package variables that they inherit from their base classes (except perhaps for the odd bit of internal caching for the sake of efficiency). Instead it's the Badger::Class object that is smart enough to go looking for package variables in all the right places, but only if you ask it to do so.

Accessing package variables via a method is obviously going to be slower than referencing them direct. The benefit comes from flexibility and ease of use (and it's generally better to optimise for programmer convenience unless you have good reason to do otherwise). In most real-world applications, performance is unlikely to be affected to any significant degree unless you're doing it often in a speed critical section of code. If this is an issue, then you can perform the more expensive variable lookup once when the object is initialised and cache the value(s) internally for other methods to use, as shown in the earlier examples with $self->{ max_volume }.

bclass($pkg)

This is an alias for class() for those times where you've already got a method or subroutine called class defined in your module.

classes($pkg)

This subroutine returns a list (in list context) or a reference to a list (in scalar context) of Badger::Class objects. As per class(), a package name or object reference should be passed as the first argument, either explicitly or implicitly by calling it as an object method.

The first Badger::Class object in the list returned represents the current class object, as would be returned by class(). Any further items in the list are Badger::Class objects representing all the base classes of the object. The order of base classes is determined by the heritage() method which implements a simplified variant of the C3 method resolution algorithm.

EXPORT HOOKS

NOTE: The terms export hook and import hook refer to the same thing and can be used interchangeably. We typically use export hook from the perspective of the exporting module, and import hook from the perspective of the importing module.

base

Allows you to define a base class or classes for the module. Multiple values can be specified by reference to an array or as a single whitespace delimited string.

    # single base class
    use Badger::Class
        base => 'Your::Base';

    # multiple base classes as list reference
    use Badger::Class
        base => ['My::Base', 'Your::Base'];

    # multiple base classes as single string
    use Badger::Class
        base => 'My::Base Your::Base';

If you accidentally put commas between the names in the string then we'll silently ignore them instead of chastising you for it. We know what you mean.

    # commas are allowed, with or without whitespace afterwards
    use Badger::Class
        base => 'My::Base,Your::Base, Another::Base';

See the base() method for further details.

mixin

This can be used to mixin subroutines, methods and/or data from another module. It works in a similar way to the regular import/export mechanism.

    package Your::Module;

    use Badger::Class
        mixin => 'Your::Mixin::Module';

You can specify multiple class using either a list reference or whitespace delimiter string, as per base.

    package Your::Module;

    use Badger::Class
        mixin => 'My::Mixin::Module Your::Mixin::Module';

The modules that you're mixing in should declare the methods that they make available for mixing using the mixins hook or mixins() method.

See the mixin() method and Badger::Mixin for further details.

mixins

This is used to declare the symbols that can be mixed into another module.

    package Your::Mixin::Module;

    use Badger::Class
        mixins => '$NAME nuts berries';

    our $NAME = 'Badger';
    sub nuts    { return 'I like nuts' }
    sub berries { return 'I like berries' }

The $NAME package variable, and nuts and berries subroutines will be exported to any module that loads Your::Mixin::Module as a mixin.

    package Your::Module;

    use Badger::Class
        mixin => 'Your::Mixin::Module';

    print $NAME;            # Badger
    print nuts();           # I like nuts
    print berries();        # I like berries

See the mixins() method and Badger::Mixin for further details.

version

This can be used to declare a version number for your module. It defines the $VERSION package variable for you along with a VERSION constant subroutine that returns the same value.

    package Your::Module;

    use Badger::Class
        version => 3.14;

    print $VERSION;                 # 3.14
    print  VERSION;                 # 3.14

    package main;

    print $Your::Module::VERSION;   # 3.14
    print  Your::Module->VERSION;   # 3.14

See the version() method for further details.

debug

This can be used to define a $DEBUG package variable and debugging() subroutine that you can use to get or set its value. It is typically used in conjunction with the Badger::Base debug() method like so:

    package Your::Module;

    use Badger::Class
        base  => 'Badger::Base',
        debug => 0;

    sub some_method {
        my $self = shift;
        $self->debug("Doing some_method()\n") if $DEBUG;
    }

See the debug() method and Badger::Debug for further details.

dumps

This is a short-cut to the dumps export hook in Badger::Debug.

constant

This can be used to define constants in your module.

    package Your::Module;

    use Badger::Class
        constant => {
            name => 'Badger',
            food => 'Nuts and Berries',
        };

    print name;     # Badger
    print food;     # Nuts and Berries

In works just like the constant module in defining constant subroutines that return the specified value. Perl resolves these at compile time so they're very efficient.

Thanks to the wonders of Perl's loosely defined object system, you can call these subroutines as object methods. In this case they're not resolved at compile time so they're no more efficient than regular method calls. However they do provide a useful mechanism for defining constants that can be redefined by subclasses.

    package Your::Amplifier;

    use Badger::Class
        constant => {
            max_volume => 10,
        };

    sub how_loud {
        my $self = shift;
        print "This amp goes up to ", $self->max_volume, "\n";
    }

    package main;

    Your::Amplifier->how_loud;  # This amp goes up to 10

This module can now be subclassed with a new max_volume defined, like so:

    package My::Amplifier;

    use Badger::Class
        base     => 'Your::Amplifier',
        constant => {
            max_volume => 11,
        };

    package main;

    My::Amplifier->how_loud;  # This amp goes up to 11

This provides an alternative to using package variables to define default configuration values for a module. The only limitation is that you can't change them once they're defined (although you can subclass the module and define a new constant). This limitation may be a Good Thing in some cases.

See the constant() method for further details.

constants

This can be used to import one or more symbols from the Badger::Constants module (or a constants module of your choosing if you subclass Badger::Class as described above in "SUBCLASSING Badger::Class").

    use Badger::Class
        constants => 'ARRAY TRUE FALSE';

    sub is_this_an_array_ref {
        my $thingy = shift;
        return ref $thingy eq ARRAY ? TRUE : FALSE;
    }

See the constants() method and Badger::Constants for further details.

words

This is a short-cut for defining a number of single-word constants.

    use Badger::Class
        words => 'yes no';

    print yes;          # yes
    print no;           # no

Defining constants for frequently used words is a good thing because it eliminates the chance of misspelling. If you misspell the name of a constant then Perl will raise an error giving you immediate notification of the problem. On the other hand, if you misspell a word in a string, then the chances are you won't find out until you next run your extensive test suite. You do have an extensive test suite don't you?

    use Badger::Class
        words => 'inclusive exclusive';

    sub do_something_goodly {
        my ($self, $params) = @_;

        # PASS: Perl throws an error about 'incluvise' bareword
        if ($params->{ mode } eq incluvise) {
            ...
        }
    }

    sub do_something_badly {
        my ($self, $params) = @_;

        # FAIL: Perl does what you tell it and has no way of
        # spotting your typo
        if ($params->{ mode } eq 'incluvise') {
            ...
        }
    }

vars

This allows you to pre-define one or more package variables. It works rather like the vars module.

    use Badger::Class
        vars => '$FOO @BAR %BAZ';

It also allows you to provide values for variables, like so:

    use Badger::Class
        vars => {
            '$FOO' => 'Hello World',
            '@BAR' => [1.618,2.718,3.142],
            '%BAZ' => { x=>10, y=>20 },
        };

See the vars() method for further information.

exports

This allows you to declare the symbols that your module can export.

    use Badger::Class
        exports => {
            all => 'foo bar',
            any => 'baz bam',
        };

See the exports() method and Badger::Exporter for further details.

throws

This can be used to set the $THROWS package variable, as used by the error handling mechanism in Badger::Base.

    package Your::Module;

    use Badger::Class
        base   => 'Badger::Base',
        throws => 'oh.noes';

    package main;

    eval {
        Your::Module->error('something has gone wrong');
    };
    print $@;       # oh.noes error - something has gone wrong

See the throws() method and Badger::Base for further information.

messages

This can be used to define a $MESSAGES package variable which references a hash array of message formats for use with the message() and related methods in Badger::Base

    package Your::Module;

    use Badger::Class
        base     => 'Badger::Base',
        messages => {
            request => 'can i haz %s?',
            denied  => 'FAIL: NO %s 4U!!!',
        };

    package main;

    print Your::Module->message( request => 'cheezburger' );
                    # can i haz cheezburger?

    Your::Module->warn_msg( denied => 'cheezburger' );
                    # FAIL: NO cheezburger 4U!!!

See the messages() method and Badger::Base for further details.

utils

This can be used to import symbols from the Badger::Utils module. This defines a number of its own utility functions, as well as providing access to a number of functions from Scalar::Util. (NOTE: only a limited number of functions from Scalar::Util at present but I plan to make Badger::Utils delegate to any symbols in any of the *::Util modules).

    use Badger::Class
        utils => 'blessed xprintf';

    sub welcome {
        my ($self, $name) = @_;

        $name = $name->get_name
            if blessed $name && $name->can('get_name');

        xprintf('Hello %s!', $name);
    }

See the utils() method and Badger::Utils for further details.

config

This can be used to define configuration options for your module. It delegates to the Badger::Class::Config module.

    package Your::Module;

    use Badger::Class
        base      => 'Badger::Base',
        accessors => 'foo bar baz wig woot toot zoot zang',
        config    => [
            'foo',                      # optional item
            'bar!',                     # mandatory item
            'baz=42',                   # item with default
            'wig|wam|bam',              # item with aliases
            'woot|pkg:WOOT',            # fallback to $WOOT pkg var
            'toot|class:WOOT',          # fallback to $WOOT class var
            'zoot|method:ZOOT',         # fallback to ZOOT() method/constant
            'zing|zang|pkg:ZING=99',    # combination of above
        ];

    sub init {
        my ($self, $config) = @_;

        # call the configure() method provided by the above
        $self->configure($config);

        return $self;
    }

The configure() method is exported into your module as a configuration method for initialising object instances. A $CONFIG package variable is also exported containing a reduced (i.e. optimised for performance) version of the configuration scheme which the configure() method uses.

codec

This can be used to import a single codec from Badger::Codecs.

    use Badger::Class
        codec => 'base64';

    my $encoded = encode('Some text');
    my $decoded = decode($encoded);

See the codec() method and Badger::Codecs for further details.

codecs

This can be used to import multiple codecs from Badger::Codecs.

    use Badger::Class
        codecs => 'base64 storable';

    my $encoded = encode_base64( encode_storable( $some_data ) );
    my $decoded = decode_storable( decode_base64( $encoded ) );

Codecs can be composed as a pipeline of other codecs. In the following example, we define a session codec which encodes data by first passing it through the storable codec (which uses the Storable freeze() subroutine) and then onto the base64 codec (which uses the MIME::Base64 encode_base64 subroutine).

    use Badger::Class
        codecs => {
            session => 'base64+storable',
        };

    my $encoded = encode_session( $some_data );
    my $decoded = decode_session( $encoded );

In case you were wondering about the significance of this particular codec combination, the Storable module can generate NULL characters in the output stream which will make some databases (e.g. Postgres) choke. Adding a second level of Base 64 encoding solves the problem.

See the codecs() method and Badger::Codecs for further details.

methods

This can be used to define methods for a class on-the-fly or patch existing subroutines or methods into a class.

    use Badger::Class
        methods => {
            foo => sub { print "This is the foo method" },
            bar => \&Some::Other::Method,
        };

alias

This can be used to define aliases to existing methods.

    use Badger::Class
        alias => {
            foo => \&bar,
            baz => 'bam',
        };

See the alias() method for further details.

slots

This can be used to define methods for list-based objects.

    use Badger::Class
        slots => 'size colour object';

See the slots() method for further details.

accessors / get_methods

This can be used to define simple read-only accessor methods for a class.

    use Badger::Class
        accessors => 'foo bar';

You can use get_methods as an alias for accessors if you prefer.

    use Badger::Class
        get_methods => 'foo bar';

See the accessors() method for further details.

mutators / set_methods

This can be used to define simple read/write mutator methods for a class.

    use Badger::Class
        mutators => 'foo bar';

You can use set_methods as an alias for mutators if you prefer.

    use Badger::Class
        set_methods => 'foo bar';

See the mutators() method for further details.

hash_methods

This can be used to define methods for accessing hash arrays inside an object

    use Badger::Class
        hash_methods => 'users addresses';

See the hash_methods() method and the hash() method in Badger::Class::Methods for further information.

init_method

This can be used to define an init() method for initialising an object. The constructed init() method stores the configuration data internally and calls each of the methods named.

    use Badger::Class
        base        => 'Badger::Base',
        init_method => 'init_foo init_bar';

    sub init_foo {
        my ($self, $config) = @_;
        ...
    }

    sub init_bar {
        my ($self, $config) = @_;
        ...
    }

It is typically used in conjunction with the config hook which defines a configure() method.

    use Badger::Class
        base        => 'Badger::Base',
        config      => 'x y',
        init_method => 'configure';

It can also be used to call initialisation methods inherited from base classes or imported from mixins.

    use Badger::Class
        base        => 'My::Base1 My::Base2',
        init_method => 'init_base1 init_base2';

See the init_method() method and the initialiser() method in Badger::Class::Methods for further information.

auto_can

This can be used to define a method that automatically generates other methods on demand.

    use Badger::Class
        auto_can => 'auto_can';

    sub auto_can {
        my ($self, $name) = @_;

        return sub {
            my $self = shift;
            print "This is the auto-generated $name method";
        }
    }

Now when you call an undefined method it will be generated on demand:

    $object->foo;       # This is the auto-generated foo method

Your method doesn't have to be called auto_can(). You can call it anything you like.

    use Badger::Class
        auto_can => 'method_maker';

    sub method_maker {
        my ($self, $name) = @_;

        #...etc...
    }

See the auto_can() method in Badger::Class::Methods for further information.

overload

This can be used as a shortcut to the overload module to overload operators for your class.

    use Badger::Class
        overload => {
            '""'     => \&text,
            bool     => sub { 1 },
            fallback => 1,
        };

as_text

This is a shortcut to the overload module. It can be used to define an auto-stringification method that generates a text representation of your object. The method can be specified by name or as a code reference.

    use Badger::Class
        as_text => 'your_text_method';

    sub your_text_method {
        my $self = shift;
        # your code
    }

is_true

This is a shortcut to the overload module. It can be used to define an method that is used for boolean truth comparisons. This can be useful in conjunction with the as_text hook to ensure that an object reference always evaluates true, even if the auto-stringification method returns a string that Perl considers false (e.g. an empty string or 0).

    use Badger::Class
        as_text => 'your_text_method',
        is_true => sub { 1 };           # always true

The method can be specified as a method name or code reference. For simple false/true values you can also specify 0 or 1 and leave it up to Badger::Class to alias it to an appropriate subroutine.

    use Badger::Class
        as_text => 'your_text_method',
        is_true => 1;                   # always true

filesystem

This can be used to load and import symbols from the Badger::Filesystem module.

    use Badger::Class
        filesystem => 'Dir File';

    my $dir = Dir('/path/to/dir');

See the filesystem() method for further details.

uber

This is a special case of the base hook which should be used when subclassing a Badger::Class class.

    package Your::Class;

    use Badger::Class
        uber => 'Badger::Class';

See the uber() method for further details.

hooks

This can be used by Badger::Class subclasses to define their own import hooks.

    package Your::Class;

    use Badger::Class
        uber  => 'Badger::Class',
        hooks => 'foo bar';

See the hooks() method for further details.

METHODS

new($package)

Constructor method for a Badger::Class object. You shouldn't ever need to call this method directly. Use the class() subroutine instead.

name() / pkg()

Returns the class (i.e. package) name.

    print class->name;          # Your::Module

This method is called automatically whenever a Badger::Class object is stringified.

    print class;                # Your::Module

The pkg() method is an alias for name() for those occasions when it reads better (for an entirely subjective definition of "better").

    print class->pkg;           # Your::Module
    class->pkg->new;            # Your::Module->new

parents()

Returns the package names of the immediate parents (base classes) of an object class.

heritage()

The heritage() method returns a list of Badger::Class objects representing each class in the inheritance chain, starting with the current class and continuing up through its superclasses.

It uses a simplified version of the C3 method resolution algorithm. See "IMPLEMENTATION NOTES" for further details if you're interested in that kind of thing.

id()

This method returns a short string used to identify the object class. This is typically used for error reporting purposes if the object doesn't explicitly define an error type (see the throws configuration option and $THROWS package variable in Badger::Base).

It generates a lower case dotted representation of the class name, with the common base part removed (Badger:: by default). For example a Badger::Example module would return example as an identifier, and Badger::Foo::Bar would return foo.bar.

base_id()

This method returns Badger by default. It is used by the id() method to determine the common base part of a module name to remove when generating an identifer for error reporting.

instance()

Method to create an instance of an object class. Delegates to the new() method for the class.

loaded()

Returns true or false to indicate if the module class is loaded or not.

load()

Loads the module class if not already loaded.

maybe_load()

A wrapper around load() which catches any errors raised by the module not being found. It returns the module name if it was loaded correctly, a false value (0) if not. If the module was found but contained syntax errors then these will be throw as errors as usual.

CLASS VARIABLE METHODS

These methods can be used to access and manipulate the symbol table for a class, to get and set regular package variables, and to work with inherited package variables (or class variables as we refer to them when used this way).

symbols()

Returns a reference to the package symbol table for the class.

    my $symbols = class->symbols;

symbol($name)

Returns a symbol table entry for a particular name.

    my $symbol = class->symbol('FOO');

import_symbol($name,$ref)

Adds a new value to the symbol table.

    # important a subroutine/method
    class->import_symbol(
        foo => sub { ... }
    );

    # importing a class variable
    class->import_symbol(
        BAR => \$bar,
    )

scalar_ref($name)

Returns a reference to the SCALAR value for a name in the symbol table.

    my $xref = class->scalar_ref('X');  # like: $xref = \$X;

array_ref()

Returns a reference to the ARRAY value for a name in the symbol table.

    my $xref = class->array_ref('X');   # like: $xref = \@X;

hash_ref()

Returns a reference to the HASH value for a name in the symbol table.

    my $xref = class->hash_ref('X');    # like: $xref = \%X;

code_ref()

Returns a reference to the CODE value for a name in the symbol table.

    my $xref = class->code_ref('X');    # like: $xref = \&X;

glob_ref()

Returns a reference to the GLOB value for a name in the symbol table.

    my $xref = class->glob_ref('X');    # like: $xref = \*X;

scalar()

Returns the SCALAR value for a name in the symbol table.

    my $xvar = class->scalar('X');      # like: $xvar = $X;

array()

Returns the ARRAY values for a name in the symbol table.

    my @xvar = class->array('X');       # like: @xvar = @X;

hash()

Returns the HASH values for a name in the symbol table.

    my %xvar = class->hash('X');        # like: %xvar = %X;

var($name,$value)

Method to get or set a scalar package variable. The leading $ sigil is not required.

    class->var( X => 10 );              # like: $X = 10
    class->var('X');                    # like: $X

var_default($name,$default)

Method to get a scalar package variable. An optional default value can be provided in case the package variable is undefined.

    class->var_default( X => 10 );      # like: $X || 10

any_var($name)

Get the value of a scalar package variable in the current class or those of any of the base classes.

    class->any_var('X');

any_var_in($names)

Looks in the current package and those of the base classes for any of the scalar variables listed in $names. The first defined value is returned, or undef if none are defined.

Multiple arguments can be specified as a list, a reference to a list or a single string of whitespace delimiter variable names (without the leading $ sigil).

    class->any_var_in('X Y Z');
    class->any_var_in('X', 'Y', 'Z');
    class->any_var_in(['X', 'Y', 'Z']);

all_vars($name)

Get all defined values of a package variable in the current package or any of the base classes. Returns a list of values in list context, or a reference to a list of values in scalar context.

    @values = class->all_vars('X');     # list context returns list
    $values = class->all_vars('X');     # scalar context returns list ref

list_vars($name)

This method return a reference to a list containing all the values defined in a particular class variable for the current class and all base classes. Package variables that reference a list will have their contents merged in.

    package A;
    our $THINGS = ['Foo', 'Bar'];

    package B;
    our $THINGS = ['Baz', 'Bam'];

    package C;
    our $THINGS = 'Wibble';

    package main;
    C->list_vars('THINGS');     # ['Wibble', 'Baz', 'Bam', 'Foo', 'Bar']

Additional arguments may be passed which are merged into the start of the list.

    B->list_vars('THINGS', 10, 20);
                                # [10, 20, 'Baz', 'Bam', 'Foo', 'Bar']

    B->list_vars('THINGS', [30, 40]);
                                # [30, 40, 'Baz', 'Bam', 'Foo', 'Bar']

This is typically used in object initialisation methods to merge any values specified as configuration parameters with those defined in package variables. These "local" configuration value are assumed to take precedence over package variables. Hence they appear at the start of the list rather than the end.

    sub init {
        my ($self, $config) = @_;

        $self->{ things } = $self->class->list_vars(
            THINGS => $config->{ things }
        );
    }

An additional list reference of things can now be passed to the constructor method.

    my $b = B->new( things => [10,20] );

hash_vars($name)

Works like list_vars() but merges references to hash arrays into a single hash array. A warning will be raised if any values are defined in the relevant package variables that don't reference hash arrays.

    package A;
    our $THINGS = {
        foo => 'Foo'
        bar => 'Bar',
    };

    package B;
    our $THINGS = {
        bar => 'New Bar',
        baz => 'Baz',
    };

    package main;
    B->hash_vars('THINGS');

The call to hash_vars('THINGS') in the example above will return a reference to a hash array containing the following items:

    {
        foo => 'Foo',
        bar => 'New Bar',
        baz => 'Baz',
    }

Note how the value for bar is taken from the B package rather than the A package because B is the more specialised class (i.e. closer in terms of the inheritance tree).

Additional arguments may be passed which are merged into the hash array. A common idiom is to use this in an object constructor or initialisation method to merge the values in package variables with any specified as configuration parameters. Values passed as argument will have precedence over those defined in package variables.

    sub init {
        my ($self, $config) = @_;

        $self->{ things } = $self->class->hash_vars(
            THINGS => $config->{ things }
        );
    }

An additional hash reference of things can now be passed to the constructor method.

    my $b = B->new( things => {
        foo => 'New Foo',
        bam => 'Bam',
    } );

The composite hash returned by hash_vars will contain:

    {
        foo => 'New Foo',
        bar => 'New Bar',
        baz => 'Baz',
        bam => 'Bam',
    }

hash_value($name,$key,$default)

Looks for a specific $key in a hash array referenced by the $name package variable in the current class or any base classes. Returns the first value found or the $default value (which can be undefined) if no relevant entries are found.

    package A;
    our $THINGS = {
        foo => 'Foo'
        bar => 'Bar',
    };

    package B;
    our $THINGS = {
        bar => 'New Bar',
        baz => 'Baz',
    };

    package main;
    print B->hash_value( THINGS => 'foo' );     # Foo
    print B->hash_value( THINGS => 'bar' );     # New Bar
    print B->hash_value( THINGS => 'baz' );     # Baz

CLASS CONFIGURATION METHODS

These methods can be used to perform various class metaprogramming tasks. They all return a $self reference allowing them to be chained together, e.g.

    $object->base($b)->version($v)->debug($d);

base(\@classes)

Method to define one or more base classes for a module. It effectively does the same thing as base.pm in adding the specified classes to the @ISA package variable;

    class->base('Your::Base::Module');

This method can be called via the base import hook.

    use Badger::Class
        base => 'Your::Base::Module';

version($n)

Method to define the version number for a class. This has the effect of setting $VERSION in the target class. It also defines a VERSION method which returns the version number.

    package Badger::Example;
    use Badger::Class 'class';
    class->version(3.14);

    package main;
    print $Badger::Example::VERSION;        # 3.14
    print  Badger::Example->VERSION;        # 3.14

This method can be called via the version import hook.

    use Badger::Class
        version => 3.14;

debug($flag)

This method can be used to enable debugging controls for a class. It defines a $DEBUG package variable set to the value of $flag and a debugging() method which can be used to enable or disable debugging.

The debugging() method generated simply calls back to the Badger::Class debugging() method.

The debug() method can be called via the debug import hook.

    use Badger::Class
        debug => 0;

The immediate benefit of using an import hook is that the definition of $DEBUG happens at compile time. That means you can safely reference $DEBUG from that point forwards without Perl warning that you're using an undefined variable.

    use Badger::Class
        debug => 0;

    sub do_something {
        my $self = shift;
        $self->debug("Doing something\n") if $DEBUG;
    }

debugging($flag)

The method can be used to get or set the value of the $DEBUG package variable for the class. Here's how you would typically use it.

    package Your::Module;

    use Badger::Class
        debug => 0;         # debugging off by default

    sub do_something {
        my $self = shift;
        $self->debug("Doing something\n") if $DEBUG;
    }

    package main;

    my $obj = Your::Module->new;
    $obj->debugging(1);     # sets $DEBUG to 1
    $obj->do_something;     # generates debugging message

constants($names)

This method can be used to import one or more symbols from the Badger::Constants module (or a constants module of your choosing if you subclass Badger::Class as described above in "SUBCLASSING Badger::Class").

    class->constants('ARRAY TRUE');

Although you can call it manually as a method from inside your code, you'll probably want to access it via the constants import hook so that the symbols are imported at compile time.

    use Badger::Class
        constants => 'ARRAY TRUE FALSE';

    sub is_this_an_array_ref {
        my $thingy = shift;
        return ref $thingy eq ARRAY ? TRUE : FALSE;
    }

See Badger::Constants for further details.

constant(\%constants)

A method to define constants, just like the constant.pm module. As with constants(), you probably want to call this via the constant import hook so that the constants are defined at compile time.

    package Your::Module;

    use Badger::Class
        constant => {
            name => 'Badger',
            food => 'Nuts and Berries',
        };

words($words)

This method is used to define a set of constant words. As with constants() and constant(), it generally only make sense to do this via the words import hook.

    use Badger::Class
        words => 'yes no';

    print yes;          # yes
    print no;           # no

vars($vars)

This allows you to pre-declare one or more package variables. This is usually called via the corresponding vars import hook.

    use Badger::Class
        vars => '$FOO @BAR %BAZ';

The method delegates to the Badger::Class::Vars module.

config($schema)

This method implements the functionality for the config export hook by delegating to the Badger::Class::Config module.

exports($symbols)

This method is used to declare what symbols the module can export. It delegates to the exports() method in Badger::Exporter.

You can provide a reference to a hash array or a list of named parameters. Each name should be one of any, all, tags, hooks or fail.

    # list of named parameters
    class->exports( any => '$FOO $BAR $BAZ' );

    # reference to hash of named parameters
    class->exports({
        any  => '$FOO $BAR $BAZ',
        all  => 'wiz bang',
        tags => {
            wam => '$ONE @TWO',
            bam => '$THREE %FOUR',
        },
        hooks => {
            ding => sub { ... },
            dong => sub { ... },
        },
    });

throws($type)

This methods sets the $THROWS package variable in the target class to the value passed as an argument. This is used by the Badger::Base error handling mechanism. See the throws() method for further details

messages(\%messages)

This method can be used to update the $MESSAGES package variable in the target class to include the messages passed as arguments, either as a list or reference to a hash array of named paramters.

    # define new class message
    class->messages( careful => 'Careful with that %s %s!' );

    # method which warns; Careful with that axe Eugene!
    sub some_method {
        my $self = shift;
        $self->warning_msg( careful => axe => 'Eugene' );
    }

The new messages will be merged into any existing $MESSAGES hash reference or a new one will be created.

utils($imports)

This method can be use to load symbols from Badger::Utils. As with other methods that load compile-time constants, it should generally be called via the utils import hook.

codecs($names)

This method can be use to load codecs from Badger::Codecs. As with other methods that load compile-time constants, it should generally be called via the codecs import hook.

See Badger::Codecs for further information.

codec($name)

A method to load a single codec from Badger::Codecs. As with codecs(), it should be called via the code import hook.

See Badger::Codecs for further information.

method($name,$code)

This method can be used to get or set a method in the target class. If a single argument is specified then it behaves just like the inbuilt can() method (which it calls). It returns a CODE reference for the method either from the class itself or one of its subclasses, or undef if the method is not implemented by the target class.

    my $method = class->method('foo');

The method can be called with two arguments to define a new method in the target class.

    class->method(
        foo => sub { ... },
    )

methods(\%methods)

This method can be used to define new methods in the target class.

    class->methods(
        foo => sub { ... },
        bar => sub { ... },
    )

alias(\%methods)

This method can be used to define aliases for existing methods in the target class. The alias can be defined as an anonymous subroutine in which case it behaves in exactly the same way as methods().

    class->alias(
        foo => sub { ... }
    );

However, it's more common to want to alias one method to another existing method:

    class->alias(
        foo => \&bar,
    );

    sub bar {
        ...
    }

You can also create aliases by name. In this case, the method will be resolved (using the method() method) to find the method in the current class or any of the base classes.

    class->alias(
        foo => 'bar',
    );

accessors($names) / get_methods($names)

This method can be used to generate accessor (read-only) methods for a class. It delegates to the accessors() method in Badger::Class::Methods.

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
    class->accessors('foo bar');
    class->accessors('foo', 'bar');
    class->accessors(['foo', 'bar']);

A method will be generated in the target class for each that returns the object member data of the same name. The code generated for each method is equivalent to this:

    sub foo {
        $_[0]->{ foo };
    }

mutators($names) / set_methods($names)

This method can be used to generate mutator (read/write) methods for a class. It delegates to the mutators() method in Badger::Class::Methods.

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
    class->mutators('foo bar');
    class->mutators('foo', 'bar');
    class->mutators(['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 then the member data is updated and the new value returned.

The code generated is equivalent to this:

    sub foo {
        @_ == 2
            ? ($_[0]->{ foo } = $_[1])
            :  $_[0]->{ foo };
    }

See Badger::Class::Methods for further discussion.

hash_methods($names)

This method can be used to generate methods for a class that manipulate internal hash arrays. It accepts the same arguments as mutators() and delegates to the hash() method in Badger::Class::Methods.

init_method($names)

This method can be used to generate a custom init() method for a class. It delegates to the initialiser() method in Badger::Class::Methods.

slots($names)

This method can be used to define methods for list-based object classes. It delegates to the mutators() method in Badger::Class::Methods.

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.

    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');

overload(\%operators)

This method provides a simple shortcut to the overload core module to implement the overload import hook.

as_text($method)

This method provides a simple wrapper around the overload() method to implement the as_text import hook.

is_true($method)

This method provides a simple wrapper around the overload() method to implement the is_true import hook.

filesystem(@symbols)

This method can be used to load symbols from Badger::Filesystem. It should generally be used via the filesystem hook.

uber($class)

This method is used when creating a subclass of the Badger::Class module (or another subclass of it). It does the same thing as the base() module in adding the $class to the @ISA package variable. It then calls the internal UBER() method to generate the class() and classes() subroutines in the subclass.

hooks($names)

This can be used by Badger::Class subclasses to define their own import hooks. For example, an import hook to set a $FOO package variable could be implemented like this.

    package Your::Class;

    use Badger::Class
        uber  => 'Badger::Class',
        hooks => 'foo';

    sub foo {
        my ($self, $value) = @_;
        $self->var( FOO => $value );
    }

INTERNAL METHODS

UBER

This method generates the class() and classes() subroutines that return Badger::Class objects when called. You shouldn't ever need to call this method directly. It is automatically called once when the Badger::Class module is first loaded. It is also called by the uber() method to generate the class() and classes() methods in modules subclassed from Badger::Class (e.g. Your::Class). In this case, the generated subroutines will return object instances of the subclass (i.e. Your::Class) instead of Badger::Class.

INTERNAL CONSTANTS

The following constants are defined for internal use. You can redefine them in subclasses to hook in different delegate modules, as shown in "SUBCLASSING Badger::Class".

CODECS

The name of the codecs module, as used by the codecs() method: Badger::Codecs

CONFIG

The name of the configuration module, as used by the config() method: Badger::Class::Config

CONSTANTS

The name of the constants method, as used by the constants() method: Badger::Constants

DEBUG

A compile time constant defined from the value of the $DEBUG package variable. To enable debugging in Badger::Class set the $DEBUG package variable before you load Badger::Class. Also be aware that most other Badger modules use Badger::Class so you should set it before you load any of them.

    BEGIN { Badger::Class::DEBUG = 1 };
    use Badger::Debug;

DEBUGGER

The name of the debug module, as used by the debug export hook: Badger::Debug

EXPORTER

The name of the exporter module, as used by the exports() method: Badger::Exporter

FILESYSTEM

The name of the filesystem module, as used by the filesystem() method: Badger::Filesystem

METHODS

The name of the methods class mixin module, as used by the methods() method: Badger::Class::Methods

MIXIN

The name of the base class mixin module, as used by the mixin() method: Badger::Mixin

UTILS

The name of the utilities module, as used by the utils() method: Badger::Utils

VARS

The name of the variables module, as used by the vars() method: Badger::Class::Vars

REALLY INTERNAL CONSTANTS

These constants are really internal. You really don't need to know about them. In fact, even I don't need to know about them. I'm only documenting then to keep Pod::Coverage quiet.

VERSION

This constant defines the name of the variable that the version() method updates. Guess what? It's set to VERSION.

LOADED

This is the name of a variable that the Badger::Class method uses to assist in autoloading modules. The default value is BADGER_LOADED. Thus, Badger::Class will define a $BADGER_LOADED package variable in your module to indicate that it was loaded by Badger.

IMPLEMENTATION NOTES

C3 Method Resolution and the heritage() Method

To determine the correct resolution order for superclasses, the heritage() method implements a simplified version of the C3 method resolution algorithm. See:

http://www.python.org/2.3/mro.html for a good introduction to the subject.
Algorithm::C3 on CPAN for an implementation in Perl
http://www.webcom.com/haahr/dylan/linearization-oopsla96.html for the original Dylan paper.

This implementation differs from the original C3 algorithm by relaxing the constraint on maintaining local precedence order in the face of a more specialised precedence order that contradicts it. What that means in simple terms can be demonstrated by the following example.

Assume A and B are base classes, while AB is a subclass of (A, B), and BA is a subclass of (B, A). If we now create a subclass ABBA of (AB, BA) then the local precedence order of AB says that A should resolve before B, while the LPO of BA says that B should come before A. The C3 algorithm will intentionally fail at this point and throw an error warning about an inconsistent heterarchy. In contrast, this implementation will resolve A before B becase the more specialised ABBA subclass defines AB before BA. AB is the winner that takes it all and BA is the loser standing small.

This implementation was originally written for the Template Toolkit where this variation in the algorithm has no relevance because none of the TT modules use multiple inheritance in an ambiguous way. The same thing applies for all the core modules in the Badger bundle which generally restrict themselves to single inheritance. Furthermore, this only affects the resolution of class variables and has no bearing on the way in which Perl resolves methods (depth-first, left-to-right in Perl 5, C3 in Perl6).

Unless you're using MI in weird and wonderful ways, then the chances are that it won't affect you. But if you do use this method in your own code then be warned of the fact that it's not a strict implementation of the C3 algorithm. However it is better than Perl 5's default implementation (in the face of conflict resolution) and has the benefit of being a smaller, simpler and faster implementation than regular C3. It's also fully deterministic (i.e. it never fails) which removes the need for any error handling (which can be tricky if you're trying to call an error method on an object which can't resolve its own methods).

AUTHOR

Andy Wardley http://wardley.org/

COPYRIGHT

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

To install Badger, copy and paste the appropriate command in to your terminal.

cpanm

cpanm Badger

CPAN shell

perl -MCPAN -e shell
install Badger

For more information on module installation, please visit the detailed CPAN module installation guide.

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