Object Reorientation

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

Talk for DrupalCamp Ghent, November 2014

Transcript

1. Object
   Reorientation
   @mathiasverraes
   

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2. Mathias
   Verraes
   Independent Consultant
   @mathiasverraes
   verraes.net
   

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3. Systems are all about
   behaviour
   

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4. State as a side effect
   

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5. Functions
   f(x, y) -> z
   

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6. What does
   it do?
   f(x, y) -> z
   

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7. Types
   f(x, y) -> z
   where
   x : "A dog named Charles"
   y : [[1, 4], [76, "D5004375571"]]
   z : WAT?!
   

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8. Types
   f(x, y) -> z
   where
   x : int
   y : int
   z : 1 | 0 | -1
   

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9. Types
   function compare($left, $right)
   {
   if($left > $right) return 1;
   elseif($left == $right) return 0;
   else return -1;
   }
   

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10. Hacklang
    function compare(int $left, int $right) : int
    {
    if($left > $right) return 1;
    elseif($left == $right) return 0;
    else return -1;
    }
    

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11. Types are
    logical
    propositions
    about your code
    

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12. Types make it
    easier for programs to
    reason
    about programs
    

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13. Tools for typing in PHP:
    Classes
    interfaces
    type hints
    

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14. Types prevent type bugs
    function send(
    $articleId, $subscriberId
    )
    send($subscriberId, $articleId) // bug
    function send(
    ArticleId $articleId, SubscriberId $subscriberId
    )
    

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15. Recurring
    pattern
    f(d : T, a, b) -> d' : T
    

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16. Recurring pattern
    function doOperation($onData, $withArg, $andArg)
    {
    // ...
    return $newData;
    }
    function otherOp($onData, $withArg)
    {
    // ...
    return $newData;
    }
    

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17. Encapsulation
    

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18. $article = [
    'title' => "Object Reorientation",
    'body' => "Encapsulate all the things",
    'author' => "@mathiasverraes",
    'published' => "no",
    ];
    $article['published'] = "yes";
    

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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,
    ];
    

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20. That's not what arrays are for
    

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21. Arrays are
    collections
    of values of the
    same type
    

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22. NOT OK
    $article = [
    'title' => "Object Reorientation",
    'body' => "Encapsulate all the things",
    'author' => "@mathiasverraes",
    'published' => false,
    ];
    

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23. OK
    $fib = [1, 1, 2, 3, 5, 8, 13];
    $articles = [
    $objectReorientation,
    $understandingFibonacci,
    ];
    $indexedArticles = [
    34 => $objectReorientation,
    951 => $understandingFibonacci,
    ];
    

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24. Encapsulation
    doOperation($onData, $withArg, $andArg)
    ->
    $object->doOperation($withArg, $andArg)
    $article->publish()
    

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25. Design objects from the
    outside
    $article = new Article($title, $body, $author);
    $article->publish();
    $this->setExpectedException(
    CantChangePublishedArticle::class
    );
    $this->rename($newTitle); // throws!
    

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26. Objects guard their own
    consistency
    $article = new Article(); // $article->setTitle($title); // $article->setBody($body); // $article->setAuthor($author); //

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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;
    }
    }
    

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28. Objects are contracts
    final class StoryUpdates
    {
    public function notify(Article $source, Subscriber $subscriber)
    {
    // ...
    }
    }
    

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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;
    }
    }
    

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30. Objects decompose
    final class TimeSlot
    {
    public function __construct(
    Time $startTime, Time $endTime
    )
    { // ... }
    }
    

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31. Object patterns
    

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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;
    }
    }
    

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33. No, you will not have too many objects.
    

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34. Trust me on that.
    

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35. Value Object
    final class Money
    {
    private $amount;
    private $currency;
    public function __construct($amount, Currency $currency)
    {
    // guards ...
    $this->amount = $amount;
    $this->currency = $currency;
    }
    }
    

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36. attracts behaviour
    final class Money
    {
    /** @return Money **/
    public function add(Money $other)
    /** @return Money[] **/
    public function allocate([6, 3, 1])
    }
    

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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!
    

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38. values objects are
    immutable
    $new_price = $jim_price->subtract($coupon);
    

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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
    );
    }
    

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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;
    }
    }
    

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41. lifecycle
    changes over
    time
    stable identity
    

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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)
    }
    

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43. Procedural
    ->
    abstractions
    into objects
    

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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, ...);
    }
    }
    

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45. $customer['id']
    vs
    $customer->getId();
    

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46. Specification
    final class CustomerHas5Orders
    {
    private $db;
    public function __construct(DB $db)
    {
    $this->db = $db;
    }
    /** @return bool */
    public function isSatisfiedBy(Customer $customer)
    {
    // ...
    }
    }
    

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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;
    }
    }
    

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48. Polymorphism
    final class TenantAStrategy implements MailingTemplateStrategy
    { /* ... */}
    final class TenantBStrategy implements MailingTemplateStrategy
    { /* ... */}
    

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49. Give up control
    $campaign = new PromotionCampagin(
    new TenantAStrategy()
    );
    tell a story
    $campaign->sendNewsletterTo(
    $customers->registeredBefore($date)
    );
    

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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, ...);
    }
    }
    

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51. looks like business
    $campaign->sendNewsletterTo(
    $customers->registeredBefore($date)
    );
    

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52. great programming is great
    Storytelling
    

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53. verraes.net
    @mathiasverraes
    

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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
    

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55. inheritance is (mostly) evil
    

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