/ 
Kavorka-0.039
River stage two • 15 direct dependents • 31 total dependents
/ Kavorka::Manual::Methods

NAME

Kavorka::Manual::Methods - method/classmethod/objectmethod keywords

DESCRIPTION

Kavorka provides the method, classmethod and objectmethod keywords for the purpose of defining methods.

The anatomy of a method:

  1. The keyword introducing the method.

  2. The method name (optional).

  3. The signature (optional).

  4. Traits (optional).

  5. The prototype (optional).

  6. The attribute list (optional).

  7. The method body.

Example:

#  (1)    (2)    (3)    (4)     (5)  (6)     (7)
   method foobar ($foo) is cool :($) :cached { return $foo + $self->bar }

#          (1)    (6)
   my $m = method { return $_[0] + $self->bar };

The Keyword

By default, only the method keyword is exported. The others can be exported by request:

use Kavorka qw( method classmethod objectmethod );

The Method Name

If present, it specifies the name of the method being defined. If no name is present, the declaration is an expression that evaluates to a reference to the method in question.

Although methods are compiled at compile-time (and variables are closed over then), methods are installed into the class at run-time. So this works:

if ($ENV{DEBUG}) {
   method foobar { ... }
}
else {
   method foobar { ... }
}

It is possible to add the method to the class at compile time using the begin trait:

method foobar but begin { ... }

This may be useful for role composition, if roles are composed before methods are defined, but the roles require certain methods to exist in your class.

It is possible to define lexical (i.e. truly private) methods using a lexical variable for a method name:

objectmethod get_name () {
   return $self->{name};
}
objectmethod my $set_name (Str $new) {
   $self->{name} = $new;
}

$obj->$set_name("Bob");
$obj->get_name;            # Bob

See also: Lexical::Accessor.

The Signature

See Kavorka::Manual::Signatures.

The method keyword has a default invocant called $self, but it does not have a type constraint, so can equally be used for class or object methods. The objectmethod keyword works the same, but does define a type constraint for $self, requiring it to be a blessed object. The classmethod keyword defines an invocant called $class which has a type constraint requiring it to be a string.

In any case, it is perfectly possible to define your own name and type constraint for the invocant:

method foo ( ClassName $me: Int $foo ) { ... }

Traits

See Kavorka::Manual::ExtendingKavorka.

Two traits for methods are bundled with Kavorka: override and fresh.

The fresh trait will throw an exception if the method you are defining already exists in the inheritance hierarchy for this class. The idea of this trait is to increase safety when subclassing.

Suppose a future release of your parent class adds a new method with the same name as one of yours, but differing functionality; your method would normally override the one in the parent class. With the fresh trait, an exception would be thrown, giving you opportunity to resolve the conflict.

The override trait does the opposite; it will throw an exception if the method being defined does not already exist.

The Prototype

See Kavorka::Manual::PrototypeAndAttributes.

Note however that prototypes are fairly useless for methods.

The Attributes

Attributes may alternatively be provided before the signature.

See Kavorka::Manual::PrototypeAndAttributes.

The method, objectmethod and classmethod keywords automatically add the :method attribute to methods.

The Method Body

This is more or less what you'd expect from the method body you'd write with sub, however the lexical variables for parameters are pre-declared and pre-populated, and invocants have been shifted off @_.

BUGS

Please report any bugs to http://rt.cpan.org/Dist/Display.html?Queue=Kavorka.

SEE ALSO

Kavorka::Manual, Kavorka::Manual::Signatures, Kavorka::Manual::PrototypeAndAttributes, Kavorka::Manual::MultiSubs, Kavorka::Manual::MethodModifiers.

AUTHOR

Toby Inkster <tobyink@cpan.org>.

COPYRIGHT AND LICENCE

This software is copyright (c) 2013-2014, 2017 by Toby Inkster.

This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.

DISCLAIMER OF WARRANTIES

THIS PACKAGE IS PROVIDED "AS IS" AND WITHOUT ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.