Object Reorientation

http://verraes.net/2014/11/object-reorientation/

Talk for DrupalCamp Ghent, November 2014

Transcript

1. Object Reorientation @mathiasverraes
2. Mathias Verraes Independent Consultant @mathiasverraes verraes.net
3. Systems are all about behaviour
4. State as a side effect
5. Functions f(x, y) -> z
6. What does it do? f(x, y) -> z
7. Types f(x, y) -> z where x : "A dog named Charles" y : [[1, 4], [76, "D5004375571"]] z : WAT?!
8. Types f(x, y) -> z where x : int y : int z : 1 | 0 | -1
9. Types function compare($left, $right) { if($left > $right) return 1; elseif($left == $right) return 0; else return -1; }
10. Hacklang function compare(int $left, int $right) : int { if($left > $right) return 1; elseif($left == $right) return 0; else return -1; }
11. Types are logical propositions about your code
12. Types make it easier for programs to reason about programs
13. Tools for typing in PHP: Classes interfaces type hints
14. Types prevent type bugs function send( $articleId, $subscriberId ) send($subscriberId, $articleId) // bug function send( ArticleId $articleId, SubscriberId $subscriberId )
15. Recurring pattern f(d : T, a, b) -> d' : T
16. Recurring pattern function doOperation($onData, $withArg, $andArg) { // ... return $newData; } function otherOp($onData, $withArg) { // ... return $newData; }
17. Encapsulation
18. $article = [ 'title' => "Object Reorientation", 'body' => "Encapsulate all the things", 'author' => "@mathiasverraes", 'published' => "no", ]; $article['published'] = "yes";
19. without encapsulation, changes propagate $article = [ 'title' => "Object Reorientation", 'body' => "Encapsulate all the things", 'author' => "@mathiasverraes", 'published' => false, ]; $publishedArticle = publish($article, 10); $publishedArticle = [ 'title' => "Object Reorientation", 'body' => "Encapsulate all the things", 'author' => "@mathiasverraes", 'published' => false, ];
20. That's not what arrays are for
21. Arrays are collections of values of the same type
22. NOT OK $article = [ 'title' => "Object Reorientation", 'body' => "Encapsulate all the things", 'author' => "@mathiasverraes", 'published' => false, ];
23. OK $fib = [1, 1, 2, 3, 5, 8, 13]; $articles = [ $objectReorientation, $understandingFibonacci, ]; $indexedArticles = [ 34 => $objectReorientation, 951 => $understandingFibonacci, ];
24. Encapsulation doOperation($onData, $withArg, $andArg) -> $object->doOperation($withArg, $andArg) $article->publish()
25. Design objects from the outside $article = new Article($title, $body, $author); $article->publish(); $this->setExpectedException( CantChangePublishedArticle::class ); $this->rename($newTitle); // throws!
26. Objects guard their own consistency $article = new Article(); // <-inconsistent $article->setTitle($title); // <-inconsistent $article->setBody($body); // <-inconsistent $article->setAuthor($author); // <-consistent
27. Objects guard their own consistency final class Article { private $title, $body, $author; public function __construct($title, $body, $author) { if(empty($title) || !is_string($title)) { throw new InvalidArgumentException; } // etc... $this->body = $body; $this->author = $author; $this->title = $title; } }
28. Objects are contracts final class StoryUpdates { public function notify(Article $source, Subscriber $subscriber) { // ... } }
29. Objects compose final class Article { private $title; private $body; private $author; public function __construct( Title $title, Body $body, Author $author ) { $this->body = $body; $this->author = $author; $this->title = $title; } }
30. Objects decompose final class TimeSlot { public function __construct( Time $startTime, Time $endTime ) { // ... } }
31. Object patterns
32. Value Object final class TwitterHandle { private $name; public function __construct($name) { if (!preg_match('/^[A-Za-z0-9_]{1,15}$/', $name)) { throw new InvalidArgumentException; } $this->name = $name; } public function __toString() { return $this->name; } }
33. No, you will not have too many objects.
34. Trust me on that.
35. Value Object final class Money { private $amount; private $currency; public function __construct($amount, Currency $currency) { // guards ... $this->amount = $amount; $this->currency = $currency; } }
36. attracts behaviour final class Money { /** @return Money **/ public function add(Money $other) /** @return Money[] **/ public function allocate([6, 3, 1]) }
37. values are immutable $jim_price = new Money(2500, new Currency('EUR')); $hannah_price = $jim_price; $coupon = new Money(500, new Currency('EUR')); $jim_price->subtract($coupon); $jim_price->equals($hannah_price); // true!
38. values objects are immutable $new_price = $jim_price->subtract($coupon);
39. values objects are immutable /** @return Money **/ public function add(Money $other) { if(!$this->hasSameCurrencyAs($other)){ throw new CantAddDifferentCurrencies; } return new Money( $this->amount + $other->amount, $this->currency ); }
40. Entity final class Article { private $id; private $title; private $published = false; public function __construct(ArticleId $id, Title $title) { $this->id = $id; $this->title = $title; } public function publish() { $this->published = true; } }
41. lifecycle changes over time stable identity
42. Repositories collect entities final class ArticleRepository { private $db; public function __construct(Database $db) /** @return Article */ public function find(ArticleId $articleId) /** @return Article[] */ public function findAll() /** @return Article[] */ public function findByAuthor(Author $author) }
43. Procedural -> abstractions into objects
44. $countOrders = DB::query( 'SELECT COUNT(*) FROM orders WHERE customerId = :customerId', [ 'customerId' => $customer['id']] ); if($countOrders > 5) { $template = 'gold.html'; sendMail($template, ...); } else { $totalAmountSpent = DB::query( 'SELECT ...', [ 'customerId' => $customer['id']] ); if($totalAmountSpent > 5000) { $template = 'silver.html'; sendMail($template, ...); } else { $template = 'bronze.html'; sendMail($template, ...); } }
45. $customer['id'] vs $customer->getId();
46. Specification final class CustomerHas5Orders { private $db; public function __construct(DB $db) { $this->db = $db; } /** @return bool */ public function isSatisfiedBy(Customer $customer) { // ... } }
47. Strategy final class MailingTemplateStrategy { //... private $strategy; public function __construct(Db $db, Mailer $mailer) { //... $this->strategy = [ 'gold.html' => new CustomerHas5Orders($db), 'silver.html' => new CustomerSpent5000EUR($db), 'bronze.html' => new CustomerBought1Product($db), ]; } public function getTemplateFor(Customer $customer) { // ... return $template; } }
48. Polymorphism final class TenantAStrategy implements MailingTemplateStrategy { /* ... */} final class TenantBStrategy implements MailingTemplateStrategy { /* ... */}
49. Give up control $campaign = new PromotionCampagin( new TenantAStrategy() ); tell a story $campaign->sendNewsletterTo( $customers->registeredBefore($date) );
50. looks like code $countOrders = DB::query( 'SELECT COUNT(*) FROM orders WHERE customerId = :customerId', [ 'customerId' => $customer['id']] ); if($countOrders > 5) { $template = 'gold.html'; sendMail($template, ...); } else { $totalAmountSpent = DB::query( 'SELECT ...', [ 'customerId' => $customer['id']] ); if($totalAmountSpent > 5000) { $template = 'silver.html'; sendMail($template, ...); } else { $template = 'bronze.html'; sendMail($template, ...); } }
51. looks like business $campaign->sendNewsletterTo( $customers->registeredBefore($date) );
52. great programming is great Storytelling
53. verraes.net @mathiasverraes
54. Links » Final Classes, Mathias Verraes » DRY is about Knowledge, Mathias Verraes » Value Objects, Tony Piper » Object Thinking, David West » Patterns of Enterprise Application Architecture, Martin Fowler » Domain-Driven Design, Eric Evans
55. inheritance is (mostly) evil