NAME

ex::monkeypatched - Experimental API for safe monkey-patching

SYNOPSIS

use ex::monkeypatched 'Third::Party::Class' => (
    clunk => sub { ... },
    eth   => sub { ... },
);

use Foo::TopLevel; # provides Foo::Bar, which isn't a module
use ex::monkeypatched -norequire => 'Foo::Bar' => (
    thwapp => sub { ... },
    urkk   => sub { ... },
);

BACKGROUND

The term "monkey patching" describes injecting additional methods into a class whose implementation you don't control. If done without care, this is dangerous; the problematic case arises when:

• You add a method to a class;

• A newer version of the monkey-patched class adds another method of the same name

• And uses that new method in some other part of its own implementation.

ex::monkeypatched lets you do this sort of monkey-patching safely: before it injects a method into the target class, it checks whether the class already has a method of the same name. If it finds such a method, it throws an exception (at compile-time with respect to the code that does the injection).

See http://aaroncrane.co.uk/talks/monkey_patching_subclassing/ for more details.

DESCRIPTION

ex::monkeypatched injects methods when you use it. There are two ways to invoke it with use: one is easy but inflexible, and the other is more flexible but also more awkward.

In the easy form, your use call should supply the name of a class to patch, and a listified hash from method names to code references implementing those methods:

use ex::monkeypatched 'Some::Class' => (
    m1 => sub { ... },  # $x->m1 on Some::Class will now run this
    m2 => sub { ... },  # $x->m2 on Some::Class will now run this
);

In the flexible form, your use call supplies a single hashref saying what methods to create. That last example can be done exactly like this:

use ex::monkeypatched { class => 'Some::Class', methods => {
    m1 => sub { ... },  # $x->m1 on Some::Class will now run this
    m2 => sub { ... },  # $x->m2 on Some::Class will now run this
} };

However, this flexible form also lets you add a method of a single name to several classes at once:

use ex::monkeypatched { method => 'm3', implementations => {
    'Some::BaseClass'     => sub { ... },
    'Some::Subclass::One' => sub { ... }
    'Some::Subclass::Two' => sub { ... },
} };

This is helpful when you want to provide a method for several related classes, with a different implementation in each of them.

The classes to be patched will normally be loaded automatically before any patching is done (thus ensuring that all their base classes are also loaded).

That doesn't work when you're trying to modify a class which can't be loaded directly; for example, the XML::LibXML CPAN distribution provides a class named XML::LibXML::Node, but trying to use XML::LibXML::Node fails. In that situation, you can tell ex::monkeypatched not to load the original class:

use ex::monkeypatched -norequire => 'XML::LibXML::Node' => (
    clunk => sub { ... },
    eth   => sub { ... },
);

# Equivalently:
use ex::monkeypatched -norequire => {
    class   => 'XML::LibXML::Node',
    methods => {
        clunk => sub { ... },
        eth   => sub { ... },
    },
};

Alternatively, you can inject methods after a class has already been loaded, using the inject method:

use ex::monkeypatched;

ex::monkeypatched->inject('XML::LibXML::Node' => (
    clunk => sub { ... },
    eth   => sub { ... },
);

# Equivalently:
ex::monkeypatched->inject({ class => 'XML::LibXML::Node', methods => {
    clunk => sub { ... },
    eth   => sub { ... },
}});

Neither of these approaches (-norequire and inject) loads the class in question, so when you use them, ex::monkeypatched is unable to guarantee that all the target class's methods have been loaded at the point the new methods are injected.

The ex:: prefix on the name of this module indicates that its API is still considered experimental. However, the underlying code has been in use in production for an extended period, and seems to be reliable.

CAVEATS

If the class you're monkeying around in uses AUTOLOAD to implement some of its methods, and doesn't also implement its own can method to accurately report which method names are autoloaded, ex::monkeypatched will incorrectly assume that an autoloaded method does not exist. The solution is to fix the broken class; implementing AUTOLOAD but not can is always an error.

AUTHOR

Aaron Crane <arc@cpan.org>

LICENCE

This library is free software; you can redistribute it and/or modify it under the terms of either the GNU General Public License version 2 or, at your option, the Artistic License.