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diff --git a/static/talks/extending_moose_yapc_na_2010/slides.vroom b/static/talks/extending_moose_yapc_na_2010/slides.vroom new file mode 100644 index 0000000..7f27df3 --- /dev/null +++ b/static/talks/extending_moose_yapc_na_2010/slides.vroom @@ -0,0 +1,399 @@ +---- config +title: Extending Moose +indent: 8 +height: 18 +width: 69 +skip: 0 + +---- center +Extending Moose + +by Jesse Luehrs (doy at tozt dot net) + +---- +== motivation +---- +moose + ++great class builder + ++lots of beginner info available +---- +using only the basic features doesn't gain you much +---- perl,i4 +package Foo; +use base qw(Class::Accessor); +__PACKAGE__->mk_accessors('bar'); +---- perl,i4 +package Foo; +use Moose; +has bar => (is => 'ro'); +---- perl,i4 +but... + ++package Foo; +use Class::Accessor 'antlers'; +has bar => (is => 'ro'); +---- +moose gives you more than this + ++* builders ++* delegation ++* roles ++* etc... +---- +but the real power of moose is in extensibility +---- +typical object systems are defined in terms of, well, object systems + ++has input_file => ( + is => 'ro', + isa => File, + coerce => 1, + required => 1, +); + ++wouldn't it be nice to be able to say what we mean? + ++has_file 'input_file'; +---- +code should be written with the intent of communicating with *humans* + ++computers are great at figuring out the details on their own + ++write code in the language of the domain rather than the language of the computer +---- +this has different levels: +---- +perl: + +a user is a hash table with a key storing the username and a key storing the password, associated with a set of functions for manipulating those hash keys while validating them and ensuring they remain consistent +---- +moose (by default): + +a user has a readonly string attribute storing the username, and a read/write Authen::Passphrase object storing the password, which password checking is delegated to +---- +but what we'd really like is: + +a user has a name, and you can ask if its password is correct +---- +moose can give us this too +---- +== the mop + ++== (meta object protocol) +---- +models classes as objects +---- +every class is represented by a metaclass + ++a normal perl object of the class Moose::Meta::Class + ++contains attributes and methods as members (objects of Moose::Meta::Attribute and Moose::Meta::Method) + ++(other stuff too, but we'll ignore that for now) +---- +== Moose::Meta::Class +---- +access these objects through Class->meta (a class method installed by "use Moose") +---- +class information is stored and manipulated through these objects + ++* "@ISA = ('Foo')" -> "$meta->superclasses('Foo')" ++* "*foo = sub { ... }" -> "$meta->add_method(foo => sub { ... })" ++* "our $foo = 'bar'" -> "$meta->add_package_symbol('$foo' => 'bar')" +---- +also provides informational methods + ++* $meta->class_precedence_list ++* $meta->has_method('foo') ++* $meta->does_role('Role') +---- +and provides other functionality specific to the mop + ++* $meta->make_immutable ++* $meta->new_object ++* Moose::Meta::Class->create_anon_class +---- +== Moose::Meta::Attribute +---- +accessed through $meta->get_attribute, etc + ++stores data associated with an object + ++also handles installing methods associated with accessing that data +---- +informational methods: + ++* $meta_attr->get_read_method ++* $meta_attr->type_constraint +---- +accessing data handled by the attribute + ++$meta_attr->get_value($obj) +---- +== Moose::Meta::Method +---- +accessed through $meta->get_method, etc + ++represents a method associated with a class + ++these are typically introspected from the symbol table, not created explicitly + ++they can be created explicitly if necessary; this is how method modifiers work +---- +so how does this all work? +---- +== metacircularity +---- +metaclasses are instances of the class Moose::Meta::Class + ++but Moose::Meta::Class is itself a class + ++so it must have a metaclass +---- +this is accomplished by two tricks +---- +compiler bootstrapping + ++write a basic version first, replace it with the actual version once the structure is in place +---- +Moose::Meta::Class has a metaclass, but it's also a Moose::Meta::Class + ++so Class->meta->meta == Class->meta +---- +but this is mostly irrelevant +---- +the idea to take away is that moose is built on top of moose + ++and so it can be extended just like any other moose object +---- +so we have this foundation, but how can we make this easy to use? +---- +== Moose::Exporter +---- +we have __PACKAGE__->meta->add_attribute(foo => (is => 'ro')) + ++but we'd like "has foo => (is => 'ro')" +---- +Moose::Exporter is a wrapper around Sub::Exporter providing moose-specific functionality + ++can curry the metaclass into helper functions + ++can pass arguments to Moose::Util::MetaRole to customize the metaclasses +---- +Moose itself uses Moose::Exporter + ++'has' is a thin wrapper around __PACKAGE__->meta->add_attribute + ++read the source to Moose.pm, it's pretty simple +---- +so the key here is that all of these metaclasses can be customized, and Moose::Exporter can wrap those customizations to make them pretty +---- +basic extensions don't even need to alter the metaclass +---- perl,i4 +package FileAttributes; +use Moose::Exporter; +use MooseX::Types::Path::Class qw(File); + +Moose::Exporter->setup_import_methods( + with_meta => ['has_file'], +); + +sub has_file { + my ($meta, $name, %options) = @_; + $meta->add_attribute( + $name, + is => 'ro', + isa => File, + coerce => 1, + %options, + ); +} +---- perl,i4 +package Foo; +use Moose; +use FileAttributes; + +has_file 'foo'; +has_file 'bar' => (required => 1); +---- +but altering metaclasses can provide more powerful abstractions +---- perl,i4 +package AtomicMethod::Role::Method; +use Moose::Role; + +around wrap => sub { + my ($orig, $self, $body, @args) = @_; + my $new_body = sub { + warn "locking...\n"; # or something more useful + my @ret = $body->(@_); # TODO: handle context properly + warn "unlocking...\n"; # or something more useful + return @ret; + }; + $self->$orig($new_body, @args); +}; +---- perl,i4 +and make it pretty + ++package AtomicMethod; +use Moose::Exporter; + +Moose::Exporter->setup_import_methods( + with_meta => [qw(atomic_method)], +); + +sub _atomic_method_meta { + my ($meta) = @_; + Moose::Meta::Class->create_anon_class( + superclasses => [$meta->method_metaclass], + roles => ['AtomicMethod::Role::Method'], + cache => 1, + )->name; +} + +sub atomic_method { + my ($meta, $name, $code) = @_; + $meta->add_method( + $name => _atomic_method_meta($meta)->wrap( + $code, + name => $name, + package_name => $meta->name, + associated_metaclass => $meta + ), + ); +} +---- perl,i4 +package Foo; +use Moose; +use AtomicMethod; + +atomic_method foo => sub { + warn "in foo\n"; +}; +---- +combining metaclass alterations can be even more powerful +---- perl,i4 +package Command::Role::Method; +use Moose::Role; +---- perl,i4 +package Command::Role::Class; +use Moose::Role; + +sub get_all_commands { + my ($self) = @_; + grep { Moose::Util::does_role($_, 'Command::Role::Method') } + $self->get_all_methods; +} + +sub has_command { + my ($self, $name) = @_; + my $method = $self->find_method_by_name($name); + return unless $method; + return Moose::Util::does_role($method, 'Command::Role::Method'); +} + +sub get_command { + my ($self, $name) = @_; + my $method = $self->find_method_by_name($name); + return unless $method; + return Moose::Util::does_role($method, 'Command::Role::Method') + ? $method + : (); +} +---- perl,i4 +package Command; +use Moose::Exporter; + +Moose::Exporter->setup_import_methods( + with_meta => ['command'], + class_metaroles => { + class => ['Command::Role::Class'], + }, +); + +sub _command_method_meta { + my ($meta) = @_; + Moose::Meta::Class->create_anon_class( + superclasses => [$meta->method_metaclass], + roles => ['Command::Role::Method'], + cache => 1, + )->name; +} + +sub command { + my ($meta, $name, $code) = @_; + $meta->add_method( + $name => _command_method_meta($meta)->wrap( + $code, + name => $name, + package_name => $meta->name, + associated_metaclass => $meta + ), + ); +} +---- perl,i4 +package Foo; +use Moose; +use Command; + +command bar => sub { ... }; +---- perl,i4 +package My::App; +use Moose; +use Foo; + +sub run { + my ($self, $cmd) = @_; + if (Foo->meta->has_command($cmd)) { + Foo->new->$cmd; + } + elsif ($cmd eq 'cmdlist') { + print join ', ', map { $_->name } Foo->meta->get_all_commands; + } +} +---- +for larger projects, providing a custom exporter can simplify things greatly +---- perl,i4 +package Mooose; +use Moose::Exporter; +use MooseX::NonMoose (); +use MooseX::Aliases (); + +my ($import, $unimport, $init_meta) = Moose::Exporter->build_import_methods( + also => ['MooseX::NonMoose', 'MooseX::Aliases'], + class_metaroles => { + class => ['My::App::Meta::Class'], + }, +); + +sub import { + strict->import; + warnings->import; + autodie->import; + feature->import(':5.10'); + MooseX::Aliases->import; + goto $import; +} + +sub unimport { + # .... (s/import/unimport/ on the above) + goto $unimport; +} + +sub init_meta { + my ($package, %options) = @_; + die unless $options{for_class}->isa('My::Base::Class'); + goto $init_meta; +} +---- +the positive side +---- +these things are easily packaged up into standalone modules + ++* MooseX::FileAttributes ++* MooseX::TransactionalMethods ++* IM::Engine::Plugin::Commands ++* Blawd::OO, TAEB::OO, etc... +---- center +any questions? |