API Design Shawn M Moore Best Practical Solutions

http://sartak.org

Thursday, September 10, 2009 Presented YAPC::Asia, 2009-09-10. Tokyo Institute of Technology, Tokyo, Japan. GoogleのテックトークでもAPI設計の話が出てました

Thursday, September 10, 2009 There is a good Google Tech Talk on "how to design an API and why it matters". There isn't a whole lot of overlap between this talk and that one. Watch that one.

http://www.youtube.com/watch?v=aAb7hSCtvGw CC-BY-SA Yuval Kogman, 2006

Thursday, September 10, 2009 At YAPC::NA 2009, this guy, Hans Dieter Pearcey aka confound aka hdp, presented a talk about Dist::Zilla.

http://www.ﬂickr.com/photos/nufn/179250512/ CC-BY-SA Yuval Kogman, 2006

Thursday, September 10, 2009 Dist::Zilla was written by this other guy, Ricardo Signes, aka rjbs.

http://www.ﬂickr.com/photos/nufn/179250812/ CC-BY-SA Hans Dieter Pearcey, 2009

Thursday, September 10, 2009 Dieter presented this slide about Dist::Zilla's pluggable design. I loved it and I wanted to devote an entire talk to its glory.

http://weftsoar.net/~hdp/dzil/ Moose Path::Dispatcher HTTP::Engine Dist::Zilla IM::Engine

今日はこれらのプロジェクトが持つクールな APIの話をします Thursday, September 10, 2009 I'm here to highlight really cool API designs that these projects have. In particular, they design for extensibility and pluggability. Extensibility is really important to the current and future success of these projects. CC-BY-SA-NC Will Spaetzel, 2005

Thursday, September 10, 2009 If you haven't noticed yet, this talk is going to be very Moose-heavy. All those modules have the Moose nature.

http://www.ﬂickr.com/photos/redune/6562798/ THE SECRET

秘訣、といってもみなさんご存じだと思いますが

Thursday, September 10, 2009 There is a poorly kept secret for designing great APIs. I hope that all of you already do this, but you probably do not do it enough. THE SECRET WRITE

大事なのはテストを書く、ということTESTS

Thursday, September 10, 2009 Write tests. WRITE TESTS WRITEWRITE TESTS TESTS WRITEWRITE TESTS TESTS 血管切れるまでテストを書いてください

Thursday, September 10, 2009 Write so many tests your ears bleed. I am not joking!

DO THIS

WRITE WRITE

WRITE WRITE WRITE WRITE WRITE WRITEWRITE WRITE WRITE WRITE WRITE WRITE

なにはなくとも、とにかくテスト

Thursday, September 10, 2009 If you remember nothing else, remember to write tests! Test!

use base 'Class::Accessor::Fast'; __PACKAGE__->mk_ro_accessors('birthday');

use Moose; has birthday => (is => 'ro');

テストを書けば使いやすいAPIかどうかがわかります

Thursday, September 10, 2009 Write tests so you can tell if your API is painful to use. Which of these would you rather be stuck with?

Make it painless for your users. Some of them might be using your module a lot. If it's tedious to use your module... Test!

使いづらいモジュールは使ってもらえませんから

Thursday, September 10, 2009 ... then you'll piss your users of. They'll leave and use some other module, or worse, ﬁnd out where you live. Test!

Thursday, September 10, 2009 This is Jesse Vincent, the nicest guy in the world :) Test!

Thursday, September 10, 2009 Test!

Thursday, September 10, 2009 Moose

package Point; use Moose;

has x => ( is => 'ro', isa => 'Num', );

この先はMooseベースの話なので少し解説

Thursday, September 10, 2009 Moose serves as the foundation for the rest of the talk, so I want to explain what it "got right" in terms of its API. These next few slides are difcult but it will get clearer and less heady, so wake up soon if you space out. Metaobject Protocol

Class::MOP

MooseはClass::MOPのラッパです

Thursday, September 10, 2009 Moose is built on top of a metaobject protocol. This is Class::MOP.

See my "Extending Moose for Applications" talk for a proper introduction to the metaobject protocol http://sartak.org/talks/yapc-na-2009/extending-moose/ Metaobject Protocol

has cache => ( is => 'ro', );

要するにクラスの各パーツはすべてオブジェクトです

Thursday, September 10, 2009 The MOP is vital to Moose's operation. Basically, it means that every part of your class is represented by an object. Metaobject Protocol

has cache => ( is => 'ro', );

Moose::Meta::Attribute

hasはMoose::Meta::Attributeのインスタンスを作ります

Thursday, September 10, 2009 When you say "has" it creates an instance of the Moose::Meta::Attribute class, which holds information like the attribute's name, its type constraint, default value, etc. Metaobject Protocol

has cache => ( is => 'ro', );

Moose::Meta::Method::Accessor これでcacheというアクセサメソッドが作られます

Thursday, September 10, 2009 The is => 'ro' option creates a "cache" method in your class. It also creates an object of class Moose::Meta::Method::Accessor to represent that "cache" method. Metaobject Protocol

class PersistentAttr extends Moose::Meta::Attribute { … }

has cache => ( metaclass => 'PersistentAttr', is => 'ro', ); Mooseのクラスを拡張すれば独自機能も追加できます

Thursday, September 10, 2009 This is important because we can subclass Moose's class to add our own special logic, such as making the cache persist across processes. Subclassing and adding logic is ordinary object- oriented programming! Metaobject Protocol

role PersistentAttr { … }

has cache => ( traits => ['PersistentAttr'], is => 'ro', ); アトリビュートオブジェクトにロールを組み込むこともできます Thursday, September 10, 2009 We can also specify roles to apply to cache's attribute object. This is slightly better because it means a single attribute can have many extensions. Just like how it's better to design with roles than subclasses in ordinary programming. MooseX

ほとんどのMooseXはMOPを利用しています

Thursday, September 10, 2009 The metaobject protocol powers most of the MooseX modules. In my opinion, the metaobject protocol is responsible for a very large part of Moose's popularity. The other reason for Moose's popularity is it enables concise class code. Sugar Layer

Mooseはシュガー層がきれいに分離しているのも特徴です Thursday, September 10, 2009 Moose also makes a very clean separation between its sugar layer and the rest of the system. Sugar Layer

my $class = get_class();

あるクラスを利用したいとします

Thursday, September 10, 2009 Say you wanted to get ahold of some class... Sugar Layer

my $class = get_class();

$class->has( birthday => ( is => 'ro', ) );

hasはメソッドではないのでこれではだめです

Thursday, September 10, 2009 Then add an attribute to it. This doesn't work because "has" is not a method. Its ﬁrst parameter is supposed to be the attribute name, not the class you're adding the attribute to. Sugar Layer

my $class = get_class();

no strict 'refs'; *{$class.'::has'}->( birthday => ( is => 'ro', ) );

だからといってhasを関数として呼ぶのはばかげています Thursday, September 10, 2009 So we have to call $class's "has" as a function. This kind of thing is ridiculous. Maybe the other class has used "no Moose" so that "has" is deleted. Or perhaps it renamed "has". Sugar Layer

my $class = get_class();

no strict 'refs'; *{$class.'::has'}->( birthday => ( is => 'ro', ) );

それに見づらいですよね

Thursday, September 10, 2009 Not to mention how ugly this mess is. Sugar Layer

Class::MOP::Class ->initialize($class) ->add_attribute( $name, %options);

hasは基本的にはadd_attributeのラッパです

Thursday, September 10, 2009 If we look at the source code of Moose, we can see "has" is basically a wrapper around the "add_attribute" method of the Class::MOP::Class instance. Sugar Layer

my $class = get_class();

$class->meta->add_attribute( birthday => ( is => 'ro', ) );

これでずいぶんマシになりました

Thursday, September 10, 2009 Much better. There's no messy syntax. This can be used outside of $class's namespace just ﬁne. This also works if class has cleaned up after Moose with "no Moose" or namespace::clean. Sugar Layer use MooseX::Declare;

class Point3D extends Point { has z => (…);

after clear { $self->z(0); } }

シュガー層が分離しているので修正も楽です

Thursday, September 10, 2009 Having a clean sugar layer means that other people can write better sugar. I like the idea of providing a separate Devel::Declare-powered sugar layer in a separate distribution. It forces you to cleanly separate the pieces. Path::Dispatcher

use Path::Dispatcher::Declarative -base;

on ['wield', qr/^\w+$/] => sub { wield_weapon($2); }

under display => sub { on inventory => sub { show_inventory }; on score => sub { show_score }; };

YourDispatcher->run('display score');

これはJifty::DispatcherをProphetで使うために書きました Thursday, September 10, 2009 Path::Dispatcher is a standalone-URI dispatcher. I wrote it because I wanted Jifty::Dispatcher for Prophet's command-line interface.

This is its sugar layer. Like Moose, it has a clean, extensible API if you want the freedom to do unusual things. Path::Dispatcher::Declarative

use Sub::Exporter -setup => { exports => [ on => \&build_on, under => \&build_under, …, ], };

もともとはSub::Exporterを使っていました

Thursday, September 10, 2009 It used to be that Path::Dispatcher::Declarative was implemented as an ordinary Sub::Exporter-using module. Path::Dispatcher::Declarative

use Sub::Exporter -setup => { exports => [ on => \&build_on, under => \&build_under, …, ], };

でもこれではまったく拡張性がありません

Thursday, September 10, 2009 This is not at all extensible. You can't change the meaning of "on" or "under" because these are hardcoded. Reusing this sugar would be painful as well. Path::Dispatcher::Builder Robert Krimen "grink"

Robert Krimenが拡張したがったので

Thursday, September 10, 2009 This was ﬁne for a few weeks, but then Robert Krimen started using Path::Dispatcher. And he wanted to extend it for a module he was writing called Getopt::Chain. Path::Dispatcher::Builder

return { on => sub { $builder->on(@_) }, under => sub { $builder->under(@_) }, …, };

サブクラス化してロジック変更できるようにしました

Thursday, September 10, 2009 Path::Dispatcher::Builder makes the sugar layer creation use OOP. This let Robert subclass Path::Dispatcher::Builder and use it for his own modules. He can reuse the regular dispatcher logic, tweak it by overriding methods, and add his own behavior. grink++

OOのシュガーは本当にいいですよ

Thursday, September 10, 2009 OO sugar is a really neat idea that I haven't seen anywhere else. HTTP::Engine HTTP::Engine->new( interface => { module => 'ServerSimple', args => { … }, request_handler => sub { … }, }, )->run;

HTTP::Engineを使うと好きなサーバを選べます

Thursday, September 10, 2009 HTTP::Engine abstracts away the various HTTP server interfaces that Perl has accumulated since HTTP was invented. The beneﬁt is in letting the user pick which server interface best ﬁts their particular needs. HTTP::Engine HTTP::Engine->new( interface => { module => 'ModPerl', args => { … }, request_handler => sub { … }, }, )->run;

マゾな人ならmod_perlを使えばいいですし

Thursday, September 10, 2009 For example, you can use mod_perl if you enjoy pain. HTTP::Engine HTTP::Engine->new( interface => { module => 'FCGI', args => { … }, request_handler => sub { … }, }, )->run;

クールな人はFastCGIを使います

Thursday, September 10, 2009 Or FastCGI if you're a cool dude. HTTP::Engine

request_handler => sub { my $request = shift; return $response; }

HTTP::Engineを使えばIOのリダイレクトなどは不要です

Thursday, September 10, 2009 HTTP::Engine works well because the code you write doesn't have to worry about redirecting I/O streams, making sense of %ENV, or any of the other crap you do when writing against a particular server module. HTTP::Engine

request_handler => sub { my $request = shift; return $response; }

HTTP::Engineなら最低限必要なことを書けばOK

Thursday, September 10, 2009 HTTP::Engine boils the web server cycle to the least common denominator. You take a request... HTTP::Engine

request_handler => sub { my $request = shift; return $response; }

リクエストを受け取ってレスポンスを返す

Thursday, September 10, 2009 … and return a response. HTTP::Engine++

新しいサーバが追加されても1行変えれば対応可能

Thursday, September 10, 2009 Can we please standardize on this? New server modules can implement an HTTP::Engine::Interface, then immediately every existing HTTP::Engine-based application can switch to it by changing only a single line of code. CC-BY-SA Hans Dieter Pearcey, 2009

Thursday, September 10, 2009 Now I want to explain why this is so awesome. Dist::Zilla

AllFiles ExtraTests InstallDirs License MakeMaker Manifest ManifestSkip MetaYAML PkgVersion PodTests PodVersion PruneCruft Readme UploadToCPAN これはよく使われるプラグインのリストです

Thursday, September 10, 2009 Here's a list of plugins used by a typical Dist::Zilla-based distribution. Dist::Zilla

Thursday, September 10, 2009 Dist::Zilla itself occasionally calls methods like this. The key bit is "plugins_with". Dist::Zilla

Thursday, September 10, 2009 plugins_with takes a role name... Dist::Zilla

Thursday, September 10, 2009 ...and selects the plugins that "do" the role. These plugins all do the "FileGatherer" role, which means the plugin adds ﬁles to a distribution. Dist::Zilla

AllFiles ExtraTests InstallDirs License $_->gather_files MakeMaker for Manifest $self->plugins_with( ManifestSkip -FileGatherer MetaYAML PkgVersion ); PodTests PodVersion PruneCruft Readme UploadToCPANgather_filesで各種プラグインが追加したファイルをまとめます Thursday, September 10, 2009 Then, dzil calls gather_files on each of these plugins so it can actually add files to the distribution. "License", "Readme", and "MetaYAML" add the respective files, "AllFiles" adds every file the author wrote. "PodTests" adds pod testing files to the distribution. Dist::Zilla

AllFiles ExtraTests InstallDirs License $_->munge_files MakeMaker for Manifest $self->plugins_with( ManifestSkip -FileMunger MetaYAML PkgVersion ); PodTests PodVersion PruneCruft Readme UploadToCPAN Dist::Zillaではこの手法をあちこちで利用しています

Thursday, September 10, 2009 Dist::Zilla uses this architecture for all of the interesting parts of building a CPAN distribution. This is "munging ﬁles", which lets plugins edit ﬁles to increase the version number, or move tests around. Request Tracker

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