/ 
Monkey-Patch-Action-0.061
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/ Monkey::Patch::Action

NAME

Monkey::Patch::Action - Wrap/add/replace/delete subs from other package (with restore)

VERSION

This document describes version 0.061 of Monkey::Patch::Action (from Perl distribution Monkey-Patch-Action), released on 2018-04-02.

SYNOPSIS

Patching package or class:

use Monkey::Patch::Action qw(patch_package);

package Foo;
sub sub1  { say "Foo's sub1" }
sub sub2  { say "Foo's sub2, args=", join(",", @_) }
sub meth1 { my $self = shift; say "Foo's meth1" }

package Bar;
our @ISA = qw(Foo);

package main;
my $h; # handle object
my $foo = Foo->new;
my $bar = Bar->new;

# replacing a subroutine
$h = patch_package('Foo', 'sub1', 'replace', sub { "qux" });
Foo::sub1(); # says "qux"
undef $h;
Foo::sub1(); # says "Foo's sub1"

# adding a subroutine
$h = patch_package('Foo', 'sub3', 'add', sub { "qux" });
Foo::sub3(); # says "qux"
undef $h;
Foo::sub3(); # dies

# deleting a subroutine
$h = patch_package('Foo', 'sub2', 'delete');
Foo::sub2(); # dies
undef $h;
Foo::sub2(); # says "Foo's sub2, args="

# wrapping a subroutine
$h = patch_package('Foo', 'sub2', 'wrap',
    sub {
        my $ctx = shift;
        say "wrapping $ctx->{package}::$ctx->{subname}";
        $ctx->{orig}->(@_);
    }
);
Foo::sub2(1,2,3); # says "wrapping Foo::sub2" then "Foo's sub2, args=1,2,3"
undef $h;
Foo::sub2(1,2,3); # says "Foo's sub2, args=1,2,3"

# stacking patches (note: can actually be unapplied in random order)
my ($h2, $h3);
$h  = patch_package('Foo', 'sub1', 'replace', sub { "qux" });
Foo::sub1(); # says "qux"
$h2 = patch_package('Foo', 'sub1', 'delete');
Foo::sub1(); # dies
$h3 = patch_package('Foo', 'sub1', 'replace', sub { "quux" });
Foo::sub1(); # says "quux"
undef $h3;
Foo::sub1(); # dies
undef $h2;
Foo::sub1(); # says "qux"
undef $h;
Foo::sub1(); # says "Foo's sub1"

Patching object:

use Monkey::Patch::Action qw(patch_package);

package Foo;
sub meth1 { say "Foo's meth1" }

package Bar;
our @ISA = qw(Foo);
sub meth2 { say "Bar's meth2" }

package main;
my $h; # handle object
my $foo1 = Foo->new;
my $foo2 = Foo->new;
my $bar1 = Bar->new;
my $bar2 = Bar->new;

# replacing a method
$h = patch_object($foo1, 'meth1', 'replace', sub { say "Foo's modified meth1" });
$foo1->meth1; # says "Foo's modified meth1"
$foo2->meth1; # says "Foo's meth1"
undef $h;
$foo1->meth1; # says "Foo's meth1"

$h = patch_object($bar1, 'meth3', 'add', sub { "Bar's meth3" });
$bar1->meth3; # says "Bar's meth3"
$bar2->meth3; # dies
undef $h;
$bar1->meth3; # dies

# deleting a method
$h = patch_object($foo1, 'meth1', 'delete');
$foo1->meth1; # dies
$foo2->meth1; # says "Foo's meth1"
undef $h;
$foo1->meth1; # says "Foo's meth1"

# wrapping a method
$h = patch_object($foo1, 'meth1', 'wrap',
    sub {
        my $ctx = shift;
        say "Wrapping $ctx->{package}::$ctx->{subname}";
        $ctx->{orig}->(@_);
    }
);
$foo1->meth1; # says "Wrapping Foo::meth1" then "Foo's meth1"
$foo2->meth1; # says "Foo's meth1"
undef $h;
$foo1->meth1; # says "Foo's meth1"

DESCRIPTION

Monkey-patching is the act of modifying a package at runtime: adding a subroutine/method, replacing/deleting/wrapping another, etc. Perl makes it easy to do that, for example:

# add a subroutine
*{"Target::sub1"} = sub { ... };

# another way, can be done from any file
package Target;
sub sub2 { ... }

# delete a subroutine
undef *{"Target::sub3"};

This module makes things even easier by helping you apply a stack of patches and unapply them later in flexible order.

FUNCTIONS

patch_package

Usage:

patch_package($package, $subname, $action, $code, @extra) => HANDLE

Patch $package's subroutine named $subname. $action is either:

  • wrap

    $subname must already exist. code is required.

    Your code receives a context hash as its first argument, followed by any arguments the subroutine would have normally gotten. Context hash contains: orig (the original subroutine that is being wrapped), subname, package, extra.

  • add

    subname must not already exist. code is required.

  • replace

    subname must already exist. code is required.

  • add_or_replace

    code is required.

  • delete

    code is not needed.

Die on error.

Function returns a handle object. As soon as you lose the value of the handle (by calling in void context, assigning over the variable, undeffing the variable, letting it go out of scope, etc), the patch is unapplied.

Patches can be unapplied in random order, but unapplying a patch where the next patch is a wrapper can lead to an error. Example: first patch (P1) adds a subroutine and second patch (P2) wraps it. If P1 is unapplied before P2, the subroutine is now no longer there, and P2 no longer works. Unapplying P1 after P2 works, of course.

patch_object

Usage:

patch_object($obj, $methname, $action, $code, @extra) => HANDLE

Basically just a wrapper for patch_package to patch "only specific object(s)". Basically it does something like this:

die "'$obj' is not an object" unless blessed($obj);
my $package = ref($obj);
patch_package($package, $methname, 'wrap',
    sub {
        my $ctx = shift;
        my $self = shift;

        my $o = $ctx->{extra}[0];
        no warnings 'numeric';
        if ($o == $self) {
            # do stuff
        } else {
            # not our target object
            $ctx->{orig}->(@_);
        }
    },
);

FAQ

Differences with Monkey::Patch?

This module is based on the wonderful Monkey::Patch by Paul Driver. The differences are:

  • This module adds the ability to add/replace/delete subroutines instead of just wrapping them.

  • Interface to patch_package() is slightly different (see previous item for the cause).

  • Using this module, the wrapper receives a context hash instead of just the original subroutine.

How to patch classes and objects?

Patching a class is basically the same as patching any other package, since Perl implements a class with a package. One thing to note is that to call a parent's method inside your wrapper code, instead of:

$self->SUPER::methname(...)

you need to do something like:

use SUPER;
SUPER::find_parent(ref($self), 'methname')->methname(...)

Patching an object is also basically patching a class/package, because Perl does not have per-object method like Ruby. But if you just want to provide a modified behavior for a certain object only, you can do something like:

patch_package($package, $methname, 'wrap',
sub {
    my $ctx = shift;
    my $self = shift;

    my $obj = $ctx->{extra}[0];
    no warnings 'numeric';
    if ($obj == $self) {
        # do stuff
    }
    $ctx->{orig}->(@_);
}, $obj);

This is basically what "patch_object" does.

HOMEPAGE

Please visit the project's homepage at https://metacpan.org/release/Monkey-Patch-Action.

SOURCE

Source repository is at https://github.com/perlancar/perl-Monkey-Patch-Action.

BUGS

Please report any bugs or feature requests on the bugtracker website https://rt.cpan.org/Public/Dist/Display.html?Name=Monkey-Patch-Action

When submitting a bug or request, please include a test-file or a patch to an existing test-file that illustrates the bug or desired feature.

SEE ALSO

Monkey::Patch

AUTHOR

perlancar <perlancar@cpan.org>

COPYRIGHT AND LICENSE

This software is copyright (c) 2018, 2017, 2012 by perlancar@cpan.org.

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