Ubuntu Manpage: Class::Method::Modifiers - Provides Moose-like method modifiers

Provided by: libclass-method-modifiers-perl_2.15-1_all

NAME

       Class::Method::Modifiers - Provides Moose-like method modifiers

VERSION

       version 2.15

SYNOPSIS

           package Child;
           use parent 'MyParent';
           use Class::Method::Modifiers;

           sub new_method { }

           before 'old_method' => sub {
               carp "old_method is deprecated, use new_method";
           };

           around 'other_method' => sub {
               my $orig = shift;
               my $ret = $orig->(@_);
               return $ret =~ /\d/ ? $ret : lc $ret;
           };

           after 'private', 'protected' => sub {
               debug "finished calling a dangerous method";
           };

           use Class::Method::Modifiers qw(fresh);

           fresh 'not_in_hierarchy' => sub {
               warn "freshly added method\n";
           };

DESCRIPTION

Method modifiers are a convenient feature from the CLOS (Common Lisp Object System) world.

In its most basic form, a method modifier is just a method that calls "$self->SUPER::foo(@_)". I for one
have trouble remembering that exact invocation, so my classes seldom re-dispatch to their base classes.
Very bad!

"Class::Method::Modifiers" provides three modifiers: "before", "around", and "after". "before" and
"after" are run just before and after the method they modify, but can not really affect that original
method. "around" is run in place of the original method, with a hook to easily call that original method.
See the "MODIFIERS" section for more details on how the particular modifiers work.

One clear benefit of using "Class::Method::Modifiers" is that you can define multiple modifiers in a
single namespace. These separate modifiers don't need to know about each other. This makes top-down
design easy. Have a base class that provides the skeleton methods of each operation, and have plugins
modify those methods to flesh out the specifics.

Parent classes need not know about "Class::Method::Modifiers". This means you should be able to modify
methods in any subclass. See Term::VT102::ZeroBased for an example of subclassing with
"Class::Method::Modifiers".

In short, "Class::Method::Modifiers" solves the problem of making sure you call "$self->SUPER::foo(@_)",
and provides a cleaner interface for it.

As of version 1.00, "Class::Method::Modifiers" is faster in some cases than Moose. See
benchmark/method_modifiers.pl in the Moose distribution.

"Class::Method::Modifiers" also provides an additional "modifier" type, "fresh"; see below.

MODIFIERS

       All modifiers let you modify one or multiple methods at a time. The names of multiple methods can be
       provided as a list or as an array-reference. Examples:

        before 'method' => sub { ... };
        before 'method1', 'method2' => sub { ... };
        before [ 'method1', 'method2' ] => sub { ... };

   before method(s) => sub { ... };
       "before" is called before the method it is modifying. Its return value is totally ignored. It receives
       the same @_ as the method it is modifying would have received. You can modify the @_ the original method
       will receive by changing $_[0] and friends (or by changing anything inside a reference).  This is a
       feature!

   after method(s) => sub { ... };
       "after" is called after the method it is modifying. Its return value is totally ignored. It receives the
       same @_ as the method it is modifying received, mostly. The original method can modify @_ (such as by
       changing $_[0] or references) and "after" will see the modified version. If you don't like this behavior,
       specify both a "before" and "after", and copy the @_ during "before" for "after" to use.

   around method(s) => sub { ... };
       "around" is called instead of the method it is modifying. The method you're overriding is passed in as
       the first argument (called $orig by convention).  Watch out for contextual return values of $orig.

       You can use "around" to:

       Pass $orig a different @_
               around 'method' => sub {
                   my $orig = shift;
                   my $self = shift;
                   $orig->($self, reverse @_);
               };

       Munge the return value of $orig
               around 'method' => sub {
                   my $orig = shift;
                   ucfirst $orig->(@_);
               };

       Avoid calling $orig -- conditionally
               around 'method' => sub {
                   my $orig = shift;
                   return $orig->(@_) if time() % 2;
                   return "no dice, captain";
               };

   fresh method(s) => sub { ... };
       (Available since version 2.00)

       Unlike the other modifiers, this does not modify an existing method.  Ordinarily, "fresh" merely installs
       the coderef as a method in the appropriate class; but if the class hierarchy already contains a method of
       the same name, an exception is thrown.  The idea of this "modifier" is to increase safety when
       subclassing.  Suppose you're writing a subclass of a class Some::Base, and adding a new method:

           package My::Subclass;
           use base 'Some::Base';

           sub foo { ... }

       If a later version of Some::Base also adds a new method named "foo", your method will shadow that method.
       Alternatively, you can use "fresh" to install the additional method into your subclass:

           package My::Subclass;
           use base 'Some::Base';

           use Class::Method::Modifiers 'fresh';

           fresh 'foo' => sub { ... };

       Now upgrading Some::Base to a version with a conflicting "foo" method will cause an exception to be
       thrown; seeing that error will give you the opportunity to fix the problem (perhaps by picking a
       different method name in your subclass, or similar).

       Creating fresh methods with "install_modifier" (see below) provides a way to get similar safety benefits
       when adding local monkeypatches to existing classes; see
       <http://aaroncrane.co.uk/talks/monkey_patching_subclassing/>.

       For API compatibility reasons, this function is exported only when you ask for it specifically, or for
       ":all".

   install_modifier $package, $type, @names, sub { ... }
       "install_modifier" is like "before", "after", "around", and "fresh" but it also lets you dynamically
       select the modifier type ('before', 'after', 'around', 'fresh') and package that the method modifiers are
       installed into. This expert-level function is exported only when you ask for it specifically, or for
       ":all".

NOTES

       All three normal modifiers; "before", "after", and "around"; are exported into your namespace by default.
       You may "use Class::Method::Modifiers ()" to avoid modifying your namespace. I may steal more features
       from Moose, namely "super", "override", "inner", "augment", and whatever the Moose folks come up with
       next.

       Note that the syntax and semantics for these modifiers is directly borrowed from Moose (the
       implementations, however, are not).

       Class::Trigger shares a few similarities with "Class::Method::Modifiers", and they even have some overlap
       in purpose -- both can be used to implement highly pluggable applications. The difference is that
       Class::Trigger provides a mechanism for easily letting parent classes to invoke hooks defined by other
       code. "Class::Method::Modifiers" provides a way of overriding/augmenting methods safely, and the parent
       class need not know about it.

   :lvalue METHODS
       When adding "before" or "after" modifiers, the wrapper method will be an lvalue method if the wrapped sub
       is, and assigning to the method will propagate to the wrapped method as expected.  For "around"
       modifiers, it is the modifier sub that determines if the wrapper method is an lvalue method.

CAVEATS

       It is erroneous to modify a method that doesn't exist in your class's inheritance hierarchy. If this
       occurs, an exception will be thrown when the modifier is defined.

       It doesn't yet play well with "caller". There are some "TODO" tests for this.  Don't get your hopes up
       though!

       Applying modifiers to array lvalue methods is not fully supported. Attempting to assign to an array
       lvalue method that has an "after" modifier applied will result in an error.  Array lvalue methods are not
       well supported by perl in general, and should be avoided.

MAJOR VERSION CHANGES

       This module was bumped to 1.00 following a complete reimplementation, to indicate breaking backwards
       compatibility. The "guard" modifier was removed, and the internals are completely different.

       The new version is a few times faster with half the code. It's now even faster than Moose.

       Any code that just used modifiers should not change in behavior, except to become more correct. And, of
       course, faster. :)

ACKNOWLEDGMENTS

       Thanks to Stevan Little for Moose, I would never have known about method modifiers otherwise.

       Thanks to Matt Trout and Stevan Little for their advice.

SUPPORT

       Bugs may be submitted through the RT bug tracker
       <https://rt.cpan.org/Public/Dist/Display.html?Name=Class-Method-Modifiers> (or
       bug-Class-Method-Modifiers@rt.cpan.org <mailto:bug-Class-Method-Modifiers@rt.cpan.org>).

AUTHOR

       Shawn M Moore <sartak@gmail.com>

CONTRIBUTORS

       •   Karen Etheridge <ether@cpan.org>

       •   Shawn M Moore <code@sartak.org>

       •   Graham Knop <haarg@haarg.org>

       •   Aaron Crane <arc@cpan.org>

       •   Peter Rabbitson <ribasushi@cpan.org>

       •   David Steinbrunner <dsteinbrunner@pobox.com>

       •   gfx <gfuji@cpan.org>

       •   Justin Hunter <justin.d.hunter@gmail.com>

       •   mannih <github@lxxi.org>

       •   Yves Orton <demerphq@gmail.com>

COPYRIGHT AND LICENSE

       This software is copyright (c) 2007 by Shawn M Moore.

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