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use strict; use warnings; package Class::Method::Modifiers; # git description: v2.13-4-g6e49964 # ABSTRACT: Provides Moose-like method modifiers # KEYWORDS: method wrap modification patch # vim: set ts=8 sts=4 sw=4 tw=115 et : our $VERSION = '2.14'; use base 'Exporter'; our @EXPORT = qw(before after around); our @EXPORT_OK = (@EXPORT, qw(fresh install_modifier)); our %EXPORT_TAGS = ( moose => [qw(before after around)], all => \@EXPORT_OK, ); BEGIN { *_HAS_READONLY = $] >= 5.008 ? sub(){1} : sub(){0}; } our %MODIFIER_CACHE; # for backward compatibility sub _install_modifier; # -w *_install_modifier = \&install_modifier; sub install_modifier { my $into = shift; my $type = shift; my $code = pop; my @names = @_; @names = @{ $names[0] } if ref($names[0]) eq 'ARRAY'; return _fresh($into, $code, @names) if $type eq 'fresh'; for my $name (@names) { my $hit = $into->can($name) or do { require Carp; Carp::confess("The method '$name' is not found in the inheritance hierarchy for class $into"); }; my $qualified = $into.'::'.$name; my $cache = $MODIFIER_CACHE{$into}{$name} ||= { before => [], after => [], around => [], }; # this must be the first modifier we're installing if (!exists($cache->{"orig"})) { no strict 'refs'; # grab the original method (or undef if the method is inherited) $cache->{"orig"} = *{$qualified}{CODE}; # the "innermost" method, the one that "around" will ultimately wrap $cache->{"wrapped"} = $cache->{"orig"} || $hit; #sub { # # we can't cache this, because new methods or modifiers may be # # added between now and when this method is called # for my $package (@{ mro::get_linear_isa($into) }) { # next if $package eq $into; # my $code = *{$package.'::'.$name}{CODE}; # goto $code if $code; # } # require Carp; # Carp::confess("$qualified\::$name disappeared?"); #}; } # keep these lists in the order the modifiers are called if ($type eq 'after') { push @{ $cache->{$type} }, $code; } else { unshift @{ $cache->{$type} }, $code; } # wrap the method with another layer of around. much simpler than # the Moose equivalent. :) if ($type eq 'around') { my $method = $cache->{wrapped}; my $attrs = _sub_attrs($code); # a bare "sub :lvalue {...}" will be parsed as a label and an # indirect method call. force it to be treated as an expression # using + $cache->{wrapped} = eval "package $into; +sub $attrs { \$code->(\$method, \@_); };"; } # install our new method which dispatches the modifiers, but only # if a new type was added if (@{ $cache->{$type} } == 1) { # avoid these hash lookups every method invocation my $before = $cache->{"before"}; my $after = $cache->{"after"}; # this is a coderef that changes every new "around". so we need # to take a reference to it. better a deref than a hash lookup my $wrapped = \$cache->{"wrapped"}; my $attrs = _sub_attrs($cache->{wrapped}); my $generated = "package $into;\n"; $generated .= "sub $name $attrs {"; # before is easy, it doesn't affect the return value(s) if (@$before) { $generated .= ' for my $method (@$before) { $method->(@_); } '; } if (@$after) { $generated .= ' my $ret; if (wantarray) { $ret = [$$wrapped->(@_)]; '.(_HAS_READONLY ? 'Internals::SvREADONLY(@$ret, 1);' : '').' } elsif (defined wantarray) { $ret = \($$wrapped->(@_)); } else { $$wrapped->(@_); } for my $method (@$after) { $method->(@_); } wantarray ? @$ret : $ret ? $$ret : (); ' } else { $generated .= '$$wrapped->(@_);'; } $generated .= '}'; no strict 'refs'; no warnings 'redefine'; no warnings 'closure'; eval $generated; }; } } sub before { _install_modifier(scalar(caller), 'before', @_); } sub after { _install_modifier(scalar(caller), 'after', @_); } sub around { _install_modifier(scalar(caller), 'around', @_); } sub fresh { my $code = pop; my @names = @_; @names = @{ $names[0] } if ref($names[0]) eq 'ARRAY'; _fresh(scalar(caller), $code, @names); } sub _fresh { my ($into, $code, @names) = @_; for my $name (@names) { if ($name !~ /\A [a-zA-Z_] [a-zA-Z0-9_]* \z/xms) { require Carp; Carp::confess("Invalid method name '$name'"); } if ($into->can($name)) { require Carp; Carp::confess("Class $into already has a method named '$name'"); } # We need to make sure that the installed method has its CvNAME in # the appropriate package; otherwise, it would be subject to # deletion if callers use namespace::autoclean. If $code was # compiled in the target package, we can just install it directly; # otherwise, we'll need a different approach. Using Sub::Name would # be fine in all cases, at the cost of introducing a dependency on # an XS-using, non-core module. So instead we'll use string-eval to # create a new subroutine that wraps $code. if (_is_in_package($code, $into)) { no strict 'refs'; *{"$into\::$name"} = $code; } else { no warnings 'closure'; # for 5.8.x my $attrs = _sub_attrs($code); eval "package $into; sub $name $attrs { \$code->(\@_) }"; } } } sub _sub_attrs { my ($coderef) = @_; local *_sub = $coderef; local $@; # this assignment will fail to compile if it isn't an lvalue sub. we # never want to actually call the sub though, so we return early. (eval 'return 1; &_sub = 1') ? ':lvalue' : ''; } sub _is_in_package { my ($coderef, $package) = @_; require B; my $cv = B::svref_2object($coderef); return $cv->GV->STASH->NAME eq $package; } 1; __END__ =pod =encoding UTF-8 =head1 NAME Class::Method::Modifiers - Provides Moose-like method modifiers =head1 VERSION version 2.14 =head1 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"; }; =head1 DESCRIPTION =for stopwords CLOS 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 C<< $self->SUPER::foo(@_) >>. I for one have trouble remembering that exact invocation, so my classes seldom re-dispatch to their base classes. Very bad! C<Class::Method::Modifiers> provides three modifiers: C<before>, C<around>, and C<after>. C<before> and C<after> are run just before and after the method they modify, but can not really affect that original method. C<around> is run in place of the original method, with a hook to easily call that original method. See the L</MODIFIERS> section for more details on how the particular modifiers work. One clear benefit of using C<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 C<Class::Method::Modifiers>. This means you should be able to modify methods in I<any> subclass. See L<Term::VT102::ZeroBased> for an example of subclassing with C<Class::Method::Modifiers>. In short, C<Class::Method::Modifiers> solves the problem of making sure you call C<< $self->SUPER::foo(@_) >>, and provides a cleaner interface for it. As of version 1.00, C<Class::Method::Modifiers> is faster in some cases than L<Moose>. See F<benchmark/method_modifiers.pl> in the L<Moose> distribution. C<Class::Method::Modifiers> also provides an additional "modifier" type, C<fresh>; see below. =head1 MODIFIERS All modifiers let you modify one or multiple methods at a time. The names of multiple methods can be provided as a list or as an array-reference. Examples: before 'method' => sub { ... }; before 'method1', 'method2' => sub { ... }; before [ 'method1', 'method2' ] => sub { ... }; =head2 before method(s) => sub { ... }; C<before> is called before the method it is modifying. Its return value is totally ignored. It receives the same C<@_> as the method it is modifying would have received. You can modify the C<@_> the original method will receive by changing C<$_[0]> and friends (or by changing anything inside a reference). This is a feature! =head2 after method(s) => sub { ... }; C<after> is called after the method it is modifying. Its return value is totally ignored. It receives the same C<@_> as the method it is modifying received, mostly. The original method can modify C<@_> (such as by changing C<$_[0]> or references) and C<after> will see the modified version. If you don't like this behavior, specify both a C<before> and C<after>, and copy the C<@_> during C<before> for C<after> to use. =head2 around method(s) => sub { ... }; C<around> is called instead of the method it is modifying. The method you're overriding is passed in as the first argument (called C<$orig> by convention). Watch out for contextual return values of C<$orig>. You can use C<around> to: =over 4 =item Pass C<$orig> a different C<@_> around 'method' => sub { my $orig = shift; my $self = shift; $orig->($self, reverse @_); }; =item Munge the return value of C<$orig> around 'method' => sub { my $orig = shift; ucfirst $orig->(@_); }; =item Avoid calling C<$orig> -- conditionally around 'method' => sub { my $orig = shift; return $orig->(@_) if time() % 2; return "no dice, captain"; }; =back =head2 fresh method(s) => sub { ... }; (Available since version 2.00) Unlike the other modifiers, this does not modify an existing method. Ordinarily, C<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 C<foo>, your method will shadow that method. Alternatively, you can use C<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 C<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 C<install_modifier> (see below) provides a way to get similar safety benefits when adding local monkeypatches to existing classes; see L<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 C<:all>. =head2 install_modifier $package, $type, @names, sub { ... } C<install_modifier> is like C<before>, C<after>, C<around>, and C<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 C<:all>. =head1 NOTES All three normal modifiers; C<before>, C<after>, and C<around>; are exported into your namespace by default. You may C<use Class::Method::Modifiers ()> to avoid modifying your namespace. I may steal more features from L<Moose>, namely C<super>, C<override>, C<inner>, C<augment>, and whatever the L<Moose> folks come up with next. Note that the syntax and semantics for these modifiers is directly borrowed from L<Moose> (the implementations, however, are not). L<Class::Trigger> shares a few similarities with C<Class::Method::Modifiers>, and they even have some overlap in purpose -- both can be used to implement highly pluggable applications. The difference is that L<Class::Trigger> provides a mechanism for easily letting parent classes to invoke hooks defined by other code. C<Class::Method::Modifiers> provides a way of overriding/augmenting methods safely, and the parent class need not know about it. =head2 :lvalue METHODS When adding C<before> or C<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 C<around> modifiers, it is the modifier sub that determines if the wrapper method is an lvalue method. =head1 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 C<caller>. There are some C<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 C<after> modifier applied will result in an error. Array lvalue methods are not well supported by perl in general, and should be avoided. =head1 MAJOR VERSION CHANGES =for stopwords reimplementation 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. :) =head1 SEE ALSO =over 4 =item * L<Class::Method::Modifiers::Fast> =item * L<Moose> =item * L<Class::Trigger> =item * L<Class::MOP::Method::Wrapped> =item * L<MRO::Compat> =item * L<CLOS|https://en.wikipedia.org/wiki/Common_Lisp_Object_System> =back =head1 ACKNOWLEDGEMENTS =for stopwords Stevan Thanks to Stevan Little for L<Moose>, I would never have known about method modifiers otherwise. Thanks to Matt Trout and Stevan Little for their advice. =head1 SUPPORT Bugs may be submitted through L<the RT bug tracker|https://rt.cpan.org/Public/Dist/Display.html?Name=Class-Method-Modifiers> (or L<bug-Class-Method-Modifiers@rt.cpan.org|mailto:bug-Class-Method-Modifiers@rt.cpan.org>). =head1 AUTHOR Shawn M Moore <sartak@gmail.com> =head1 CONTRIBUTORS =for stopwords Karen Etheridge Shawn M Moore Graham Knop Aaron Crane Peter Rabbitson David Steinbrunner gfx Justin Hunter mannih =over 4 =item * Karen Etheridge <ether@cpan.org> =item * Shawn M Moore <code@sartak.org> =item * Graham Knop <haarg@haarg.org> =item * Aaron Crane <arc@cpan.org> =item * Peter Rabbitson <ribasushi@cpan.org> =item * David Steinbrunner <dsteinbrunner@pobox.com> =item * gfx <gfuji@cpan.org> =item * Justin Hunter <justin.d.hunter@gmail.com> =item * mannih <github@lxxi.org> =back =head1 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. =cut