Kavorka::Manual::Methods(3pm)

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.