Introduction to SOLID - PHPOxford

Talk presented at PHPOxford, January 2017

Transcript

1. S O L I D
   Introduction to SOLID - @garethellis
   INTRODUCTION TO SOLID
   PHP OXFORD, JANUARY 2017
   Gareth Ellis / @garethellis
   

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2. S O L I D
   Introduction to SOLID - @garethellis
   FIVE LITTLE LETTERS
   

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3. S O L I D
   Introduction to SOLID - @garethellis
   WHAT IS SOLID?
   

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4. S O L I D
   Introduction to SOLID - @garethellis
   SOLID IS NOT SPECIFIC TO PHP
   

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5. S O L I D
   Introduction to SOLID - @garethellis
   

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6. S O L I D
   Introduction to SOLID - @garethellis
   READING VS WRITING
   

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7. S O L I D
   Introduction to SOLID - @garethellis
   SINGLE RESPONSIBILITY PRINCIPLE (SRP)
   "A class should have only one reason to
   change."
   

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8. S O L I D
   Introduction to SOLID - @garethellis
   

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9. S O L I D
   Introduction to SOLID - @garethellis
   class UserRegistrationController
   {
   public function register(Request $request, Response $response)
   {
   //create a user entity from the request data
   $user = $this­>createUserFromRequest($request);
   //save in database
   $this­>userRepository­>save($user);
   //send notification to user
   $this­>email
   ­>to($user­>email())
   ­>subject("Welcome!")
   ­>send();
   return $this­>successfulResponse($response);
   }
   }
   

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10. S O L I D
    Introduction to SOLID - @garethellis
    class UserRegistration
    {
    public function __construct(
    UserRepository $userRepository,
    Email $email
    )
    {
    $this­>userRepository = $userRepository;
    $this­>email = $email;
    }
    public function register(User $user)
    {
    //save in database
    $this­>userRepository­>save($user);
    //send notification to user
    $this­>email
    ­>to($user­>email())
    ­>subject("Welcome!")
    ­>send();
    }
    }
    }
    

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11. S O L I D
    Introduction to SOLID - @garethellis
    class UserRegistration
    {
    public function __construct(
    UserRegistrationStorage $storage,
    UserRegistrationWelcomeEmail $welcomeEmail
    )
    {
    $this­>storage = $storage;
    $this­>welcomeEmail = $welcomeEmail;
    }
    public function register(User $user)
    {
    //save in database
    $this­>storage­>save($user);
    //send notification to user
    $this­>welcomeEmail­>email($user);
    }
    }
    

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12. S O L I D
    Introduction to SOLID - @garethellis
    OPEN/CLOSED PRINCIPLE (OCP)
    “So ware entities … should be open for
    extension, but closed for modification.”
    

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13. S O L I D
    Introduction to SOLID - @garethellis
    

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14. S O L I D
    Introduction to SOLID - @garethellis
    "CLOSED FOR MODIFICATION"
    

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15. S O L I D
    Introduction to SOLID - @garethellis
    YAGNI
    

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16. S O L I D
    Introduction to SOLID - @garethellis
    "OPEN FOR EXTENSION"
    

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17. S O L I D
    Introduction to SOLID - @garethellis
    IT'S NOT (NECESSARILY) ABOUT INHERITANCE
    

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18. S O L I D
    Introduction to SOLID - @garethellis
    FAVOUR COMPOSITION OVER INHERITANCE
    

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19. S O L I D
    Introduction to SOLID - @garethellis
    abstract class Duck {
    public function swim() { /** swim like a duck! */ }
    public function quack() { /** quack like a duck! */ }
    public function fly() { /** fly like a duck! */ }
    }
    class Mallard extends Duck {}
    class Eider extends Duck {}
    class Mandarin extends Duck {}
    

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20. S O L I D
    Introduction to SOLID - @garethellis
    class RubberDuck extends Duck {
    public function swim() { /** float */ }
    public function quack() { /** squeak */ }
    public function fly() { /** do nothing */ }
    public function debug($code) { /** debug the code! */ }
    }
    

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21. S O L I D
    Introduction to SOLID - @garethellis
    class WoodenToyDuck extends Duck {
    public function swim() { /** float */ }
    public function quack() { /** do nothing */ }
    public function fly() { /** do nothing */ }
    }
    

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22. S O L I D
    Introduction to SOLID - @garethellis
    interface Swimming { public function swim(); }
    interface Quacking { public function quack(); }
    interface Flying { public function fly(); }
    

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23. S O L I D
    Introduction to SOLID - @garethellis
    interface Quacking { public function quack(); }
    class QuackingDuck implements Quacking {
    public function quack() { /** quack like a real duck */ }
    }
    class MuteDuck implements Quacking {
    public function quack() { /** do nothing */ }
    }
    class SqueakingDuck implements Quacking {
    public function quack() { /** squeak like a rubber duck */ }
    }
    

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24. S O L I D
    Introduction to SOLID - @garethellis
    class Eider {
    function __construct(
    Swimming $swimming,
    Quacking $quacking,
    Flying $flying
    ) {
    $this­>swimming = $swimming;
    $this­>quacking = $quacking;
    $this­>flying = $flying;
    }
    public function swim() {
    $this­>swimming­>swim();
    }
    public function quack() {
    $this­>quacking­>quack();
    }
    public function fly() {
    $this­>flying­>fly();
    }
    }
    

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25. S O L I D
    Introduction to SOLID - @garethellis
    class Ooooooh implements Quacking {
    public function quack() {
    /** make an awesome ooooh noise like an eider duck */
    }
    }
    new Eider(new SwimmingDuck, new Ooooooh, new FlyingDuck);
    

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26. S O L I D
    Introduction to SOLID - @garethellis
    THAT'S THE STRATEGY PATTERN
    

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27. S O L I D
    Introduction to SOLID - @garethellis
    INTRODUCING THE DECORATOR PATTERN
    

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28. S O L I D
    Introduction to SOLID - @garethellis
    class ExampleMiddleware
    {
    public function __invoke($request, $response, $next)
    {
    $response­>getBody()­>write('BEFORE');
    $response = $next($request, $response);
    $response­>getBody()­>write('AFTER');
    return $response;
    }
    }
    From the SlimPHP documentation
    

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29. S O L I D
    Introduction to SOLID - @garethellis
    

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30. S O L I D
    Introduction to SOLID - @garethellis
    SANDWICHES
    

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31. S O L I D
    Introduction to SOLID - @garethellis
    DECORATOR EXAMPLE
    Integrate an application with an API
    API uses OAuth2 for auth
    Have to send a valid OAuth2 token with each API call
    Tokens are valid for 48 hours
    

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32. S O L I D
    Introduction to SOLID - @garethellis
    interface AccessTokenRepository {
    get(): AccessToken
    }
    class ApiRepository implements AccessTokenRepository {
    function __construct(Provider $provider) {
    $this­>provider = $provider;
    }
    public function get(): AccessToken {
    return $this­>provider­>getAccessToken();
    }
    }
    

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33. S O L I D
    Introduction to SOLID - @garethellis
    class StorageRepository implements AccessTokenRepository {
    function __construct(
    TokenStorage $storage,
    AccessTokenRepository $repository
    ) {
    $this­>storage = $provider;
    $this­>repository = $repository;
    }
    public function get(): AccessToken {
    $token = $this­>storage­>get();
    if ($token­>isValid()) {
    return $token;
    }
    $token = $this­>repository­>get();
    $this­>storage­>save($token);
    return $token;
    }
    }
    

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34. S O L I D
    Introduction to SOLID - @garethellis
    $tokenStorage = new SomeStorageImplementation;
    $apiRepository = new ApiRepository(new Provider);
    $storageRepository = new StorageRepository($tokenStorage, $apiRepository);
    $token = $storageRepository­>get();
    

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35. S O L I D
    Introduction to SOLID - @garethellis
    INTRODUCING THE OBSERVER PATTERN
    

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36. S O L I D
    Introduction to SOLID - @garethellis
    class UserRegistration
    {
    public function __construct(
    UserRegistrationStorage $storage,
    UserRegistrationWelcomeEmail $welcomeEmail
    )
    {
    $this­>storage = $storage;
    $this­>welcomeEmail = $welcomeEmail;
    }
    public function register(User $user)
    {
    //save in database
    $this­>storage­>save($user);
    //send notification to user
    $this­>welcomeEmail­>email($user);
    }
    }
    

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37. S O L I D
    Introduction to SOLID - @garethellis
    interface UserRegistrationListener { public function handleNew(User $user)
    class UserRegistration
    {
    public function __construct(array $listeners)
    {
    $this­>listeners = $listeners;
    }
    public function register(User $user)
    {
    foreach ($this­>listeners as $listener) {
    $listener­>handleNew($user);
    }
    }
    }
    $service = new UserRegistrationService([
    new UserRegistrationStorage,
    new UserRegistrationWelcomeEmail,
    new UserRegistrationWelcomeSMS
    ]);
    $service­>register($user);
    

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38. S O L I D
    Introduction to SOLID - @garethellis
    LISKOV SUBSTITUTION PRINCIPLE (LSP)
    “Objects in a program should be
    replaceable with instances of their
    subtypes without altering the correctness
    of that program.”
    

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39. S O L I D
    Introduction to SOLID - @garethellis
    LISKOV SUBSTITUTION PRINCIPLE (LSP)
    "If S is a subtype of T, then objects of type T
    in a program may be replaced with objects
    of type S without altering any of the
    desirable properties of that program"
    

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40. S O L I D
    Introduction to SOLID - @garethellis
    

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41. S O L I D
    Introduction to SOLID - @garethellis
    BEHAVIOUR, BEHAVIOUR, BEHAVIOUR
    

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42. S O L I D
    Introduction to SOLID - @garethellis
    class Rectangle {
    private $height;
    private $width;
    function __construct(int $height, int $width) {
    $this­>height = $height;
    $this­>width = $width;
    }
    public function setHeight(int $height) {
    $this­>height = $height;
    }
    public function setWidth(int $width) {
    $this­>width = $width;
    }
    public function getHeight() { return $this­>height; }
    public function getWidth() { return $this­>width; }
    }
    

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43. S O L I D
    Introduction to SOLID - @garethellis
    function someFunction(Rectangle $rectangle) {
    $rectangle­>setHeight(10);
    }
    $rectangle = new Rectangle(30,20);
    someFunction($rectangle);
    var_dump($rectangle­>getHeight()); // now 10
    var_dump($rectangle­>getWidth()); // still 20
    

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44. S O L I D
    Introduction to SOLID - @garethellis
    class Square extends Rectangle {
    private $heightAndWidth;
    function __construct(int $heightAndWidth) {
    $this­>heightAndWidth = $heightAndWidth;
    }
    public function setHeight(int $height) {
    $this­>heightAndWidth = $height;
    }
    public function setWidth(int $width) {
    $this­>heightAndWidth = $width;
    }
    public function getHeight() { return $this­>heightAndWidth; }
    public function getWidth() { return $this­>heightAndWidth; }
    }
    

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45. S O L I D
    Introduction to SOLID - @garethellis
    function someFunction(Rectangle $rectangle) {
    $rectangle­>setHeight(10);
    }
    $square = new Square(20);
    someFunction($square);
    var_dump($square­>getHeight()); // 10
    var_dump($square­>getWidth()); // also 10
    

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46. S O L I D
    Introduction to SOLID - @garethellis
    DESIGN BY CONTRACT
    

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47. S O L I D
    Introduction to SOLID - @garethellis
    POST-CONDITIONS OF Rectangle::setHeight() METHOD
    The height of the rectangle has changed. The width of the
    rectangle remains unchanged.
    PRE-CONDITIONS OF Rectangle::setHeight() METHOD
    There is a rectangle with a given height and width
    

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48. S O L I D
    Introduction to SOLID - @garethellis
    FAVOUR COMPOSITION OVER INHERITANCE
    

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49. S O L I D
    Introduction to SOLID - @garethellis
    INTERFACE SEGREGATION PRINCIPLE (ISP)
    “Many client-specific interfaces are better
    than one general-purpose interface.”
    

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50. S O L I D
    Introduction to SOLID - @garethellis
    

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51. S O L I D
    Introduction to SOLID - @garethellis
    SEARCH FILTERS EXAMPLE
    App contains pages with lists of "things"
    We had to include various search options on each list
    Option types included dropdowns, free text, date ranges,
    etc
    

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52. S O L I D
    Introduction to SOLID - @garethellis
    interface Filter
    {
    /**
    * @param \Cake\Network\Request $request
    * @param \Cake\ORM\Query $query
    */
    public function buildQueryFrom(Request $request, Query $query): Query
    }
    

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53. S O L I D
    Introduction to SOLID - @garethellis
    class FilterCollection implements Filter
    {
    /**
    * @var Filter[]
    */
    private $filters;
    public function add(Filter $filter) {
    $this­>filters[] = $filter;
    }
    public function buildQueryFrom(Request $request, Query $query): Query
    foreach ($this­>filters as $filter) {
    $query = $filter­>buildQueryFrom($request, $query);
    }
    return $query;
    }
    }
    

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54. S O L I D
    Introduction to SOLID - @garethellis
    class FreeText implements Filter
    {
    function __construct(string $tableAlias, string $fieldName) {
    $this­>tableAlias = $tableAlias;
    $this­>fieldName = $fieldName;
    }
    public function buildQueryFrom(Request $request, Query $query): Query
    {
    if ($request­>query($this­>fieldName)) {
    return $query­>where([
    "{$this­>tableAlias}.{$this­>fieldName} LIKE"
    => "%". $request­>query($this­>fieldName) . "%"
    ]);
    }
    return $query;
    }
    }
    

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55. S O L I D
    Introduction to SOLID - @garethellis
    $filterCollection­>add(
    new FreeText("BlogPosts", "title")
    );
    

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56. S O L I D
    Introduction to SOLID - @garethellis
    WHAT IF THE USER SEARCHES FOR "0"?
    if ($request­>query($this­>fieldName))
    

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57. S O L I D
    Introduction to SOLID - @garethellis
    WHAT IF THE USER SEARCHES FOR "0"?
    if (
    $request­>query($this­>fieldName) !== null
    && $request­>query($this­>fieldName) !== ""
    )
    

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58. S O L I D
    Introduction to SOLID - @garethellis
    interface Filter {
    /**
    * @param \App\Filter\SearchParameters $searchParameters
    * @param \Cake\ORM\Query $query
    */
    public function buildQueryFrom(
    SearchParameters $searchParameters,
    Query $query
    ): Query;
    }
    interface SearchParameters {
    public function has($parameterName): bool;
    public function value($parameterName);
    }
    

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59. S O L I D
    Introduction to SOLID - @garethellis
    class QueryStringSearchParameters implements SearchParameters
    {
    private $request;
    public function __construct(Request $request)
    {
    $this­>request = $request;
    }
    public function has(string $parameterName): bool
    {
    return $this­>request­>query($parameterName) !== null
    && $this­>request­>query($parameterName) !== "";
    }
    public function value(string $parameterName)
    {
    if (!$this­>has($parameterName)) {
    throw new SearchParameterNotFound("No such search parameter"
    }
    return $this­>request­>query($parameterName);
    }
    }
    

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60. S O L I D
    Introduction to SOLID - @garethellis
    WHAT IF THE USER SEARCHES FOR "0"?
    if ($searchParams­>has($this­>fieldName))
    

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61. S O L I D
    Introduction to SOLID - @garethellis
    WHAT DOES "INTERFACE" MEAN ANYWAY?
    interface SearchParameters {
    public function has($parameterName): bool;
    public function value($parameterName);
    }
    

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62. S O L I D
    Introduction to SOLID - @garethellis
    class Eider {
    function __construct(
    Swimming $swimming,
    Quacking $quacking,
    Flying $flying
    ) {
    $this­>swimming = $swimming;
    $this­>quacking = $quacking;
    $this­>flying = $flying;
    }
    public function swim() {
    $this­>swimming­>swim();
    }
    public function quack() {
    $this­>quacking­>quack();
    }
    public function fly() {
    $this­>flying­>fly();
    }
    }
    

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63. S O L I D
    Introduction to SOLID - @garethellis
    CLASSES HAVE IMPLICIT INTERFACES
    interface Of_Class_Eider {
    public function swim();
    public function quack();
    public function fly();
    }
    

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64. S O L I D
    Introduction to SOLID - @garethellis
    “MANY CLIENT-SPECIFIC INTERFACES TYPES ARE BETTER
    THAN ONE GENERAL-PURPOSE INTERFACE TYPE.”
    - Dan Ackroyd, PHP NW 2016
    

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65. S O L I D
    Introduction to SOLID - @garethellis
    TYPES 101
    ...a type is a classification of data which
    tells the compiler how the programmer
    intends to use the data...
    - Wikipedia
    

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66. S O L I D
    Introduction to SOLID - @garethellis
    PHP TYPES - OBJECTS
    Abstract types interface Filter
    abstract class Duck
    Concrete types
    (classes)
    class FreeText implements
    Filter
    class Mallard extends Duck
    class Eider
    

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67. S O L I D
    Introduction to SOLID - @garethellis
    PHP TYPES - SCALARS
    Integers
    Floats
    1
    3.14
    Strings "ducks are awesome"
    Booleans true
    false
    Arrays [1, 3.14, "ducks are awesome"]
    

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68. S O L I D
    Introduction to SOLID - @garethellis
    class FormHelper {
    public function datePicker(string $fieldName, array $options = [])
    {
    if (isset($options["isRequiredField"])
    && $options["isRequiredField"] === true) {
    //do something
    }
    //do something to render a datepicker field
    }
    }
    $formHelper­>datePicker("birthday", [
    "isReqieredFeild" => true, //oops I mis­spelled it!
    ]);
    

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69. S O L I D
    Introduction to SOLID - @garethellis
    class DatePickerOptions {
    private $isRequiredField = false;
    public function setRequiredField(bool $isRequired) {
    $this­>isRequiredField = $isRequired;
    }
    public function isRequiredField(): bool {
    return $this­>isRequiredField;
    }
    private $label = "My date picker":
    public function setLabel(string $label) {
    if (strlen($label) > 25) {
    throw new InvalidArgumentException("Label too long!");
    }
    $this­>label = $label;
    }
    public function label(): string {
    return $this­>label;
    }
    }
    

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70. S O L I D
    Introduction to SOLID - @garethellis
    class FormHelper {
    public function datePicker(
    string $fieldName,
    DatePickerOptions $options
    ) {
    if ($options­>isRequiredField()) {
    //do something
    }
    //do something to render a datepicker field
    }
    }
    $options = new DatePickerOptions;
    $options­>setIsRequiredField(true)
    $options­>setLabel("When is your birthday?");
    $formHelper­>datePicker("birthday", $options);
    

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71. S O L I D
    Introduction to SOLID - @garethellis
    function connect(
    string $hostname,
    int $port,
    bool $persist = false,
    bool $enableAwesomeness = true,
    bool $disableFluxCapacitor = false
    ): Connection {
    return new Connection(/** do something with arguments */);
    }
    $connection = connect("myawesomeserver.com", 123, true, false, true);
    

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72. S O L I D
    Introduction to SOLID - @garethellis
    class ConnectionFactory {
    private $persist = false;
    function __construct(string $host, int $port) {
    $this­>host = $host;
    $this­>port = $port;
    }
    public function enablePersist(): ConnectionFactory {
    $this­>persist = true;
    return $this;
    }
    public function disablePersist(): ConnectionFactory {
    $this­>persist = false;
    return $this;
    }
    public function getConnection(): Connection {
    return connect($this­>host, $this­>port,
    $this­>persist, $this­>awesomeness, $this­>fluxCapacitor);
    }
    }
    

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73. S O L I D
    Introduction to SOLID - @garethellis
    (new ConnectionFactory("myawesomehost.com", 123))
    ­>enablePersist()
    ­>enableAwesomeness()
    ­>disableFluxCapacitor()
    ­>getConnection();
    

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74. S O L I D
    Introduction to SOLID - @garethellis
    DEPENDENCY INVERSION (DI) PRINCIPLE
    “Depend upon abstractions, [not]
    concretions.”
    

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75. S O L I D
    Introduction to SOLID - @garethellis
    

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76. S O L I D
    Introduction to SOLID - @garethellis
    class Eider {
    function __construct() {
    $this­>swimming = new SwimmingDuck;
    $this­>quacking = new QuackingDuck;
    $this­>flying = new FlyingDuck;
    }
    public function swim() {
    $this­>swimming­>swim();
    }
    public function quack() {
    $this­>quacking­>quack();
    }
    public function fly() {
    $this­>flying­>fly();
    }
    }
    

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77. S O L I D
    Introduction to SOLID - @garethellis
    class Eider {
    function __construct(
    SwimmingDuck $swimming,
    QuackingDuck $quacking,
    FlyingDuck $flying
    ) {
    $this­>swimming = $swimming;
    $this­>quacking = $quacking;
    $this­>flying = $flying;
    }
    }
    

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78. S O L I D
    Introduction to SOLID - @garethellis
    DEPENDENCY INVERSION IS NOT
    (NECESSARILY) ABOUT INTERFACES
    

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79. S O L I D
    Introduction to SOLID - @garethellis
    DEPENDENCY INVERSION IS NOT
    (NECESSARILY) ABOUT OBJECTS
    

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80. S O L I D
    Introduction to SOLID - @garethellis
    class MysqlConnectionFactory()
    {
    function __construct() {
    $this­>username = "database_username";
    $this­>password = "my_password";
    }
    public function create(): PDO {
    return new PDO(
    "mysql:host=database.server",
    $this­>username,
    $this­>password
    );
    }
    }
    

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81. S O L I D
    Introduction to SOLID - @garethellis
    class MysqlConnectionFactory()
    {
    function __construct(string $username, string $password) {
    $this­>username = $username;
    $this­>password = $password;
    }
    public function create(): PDO {
    return new PDO(
    "mysql:host=database.server",
    $this­>username,
    $this­>password
    );
    }
    }
    

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82. S O L I D
    Introduction to SOLID - @garethellis
    // Without dependency injection
    new Eider;
    vs
    // With dependency injection
    new Eider(new SwimmingDuck, new Ooooooh, new FlyingDuck);
    

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83. S O L I D
    Introduction to SOLID - @garethellis
    DEPENDENCY INVERSION IS NOT ABOUT
    DEPENDENCY INJECTION CONTAINERS
    

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84. S O L I D
    Introduction to SOLID - @garethellis
    IN SUMMARY
    

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85. S O L I D
    Introduction to SOLID - @garethellis
    OPTIMIZE FOR READING
    

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86. S O L I D
    Introduction to SOLID - @garethellis
    KEEP CLASSES SMALL AND SPECIALIZED
    

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87. S O L I D
    Introduction to SOLID - @garethellis
    FAVOUR COMPOSITION OVER INHERITANCE
    

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88. S O L I D
    Introduction to SOLID - @garethellis
    USE SPECIFIC TYPES
    

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89. S O L I D
    Introduction to SOLID - @garethellis
    KEEP COUPLING AS LOOSE AS POSSIBLE
    

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90. S O L I D
    Introduction to SOLID - @garethellis
    KNOW YOUR TRADE-OFFS
    

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91. S O L I D
    Introduction to SOLID - @garethellis
    THANKS!
    by Derick Bailey
    Licensed under a
    @garethellis
    garethellis@gmail.com
    SOLID Motivational Posters
    Creative Commons Attribution-Share Alike 3.0 United States License
    

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92. S O L I D
    Introduction to SOLID - @garethellis
    FURTHER READING
    book
    paper by Robert C.
    Martin
    talk by
    Dan Ackroyd @ PHPNW 2016 (slides)
    talk by Rob Allen @
    PHPNW 2013 (video)
    (RSPB)
    Head-First Design Patterns
    The Liskov Substitution Principle
    Interface Segregation - the Forgotten "I" in SOLID
    Introducing Dependency Injection
    Eider duck
    

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