Provided by: libbadger-perl_0.16-3_all 
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 identifier 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 parameters.
# 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 because 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
Copyright (C) 1996-2009 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.
perl v5.36.0 2023-08-28 Badger::Class(3pm)