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The true value of objects

The true value of objects

Although the latest PHP versions provide us with enough types and keywords to enable object oriented development, the language itself is not truly object oriented. In pure object oriented languages, like Java, almost everything is an object. Even primitives have their object equivalent. Concepts that first look like simple values, can in fact be modelled as objects. This enables us to add a lot of behaviour to them. These so called Value Objects make our code more readable, elegant, maintainable and dry. We will explore the possibilities and advantages of these Value Objects together, guided by some real world code samples.

Stijn Vannieuwenhuyse

June 26, 2015
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  1. class Money { private $amount; private $currency; public function __construct($amount,

    $currency) { $this->amount = $amount; $this->currency = $currency; } public function getAmount() { return $this->amount; } public function getCurrency() { return $this->currency; } }
  2. $a = new Money(5.00, "EUR"); $b = new Money(5.00, "EUR");

    $c = new Money(4.23, "EUR"); $d = new Money(5.00, "USD"); $a === $b; //false $a == $b; //true $a == $c; //false $a == $d; //false
  3. $amsterdam = new City( "Amsterdam", "Netherlands", 4.8951679, 52.3702157 ); class

    City { private $latitude; private $longitude; //other fields public function __construct( $name, $country, $latitude, $longitude ) { $this->latitude = $latitude; $this->longitude = $longitude; //other assignments } //getters }
  4. class Coordinate { private $latitude; private $longitude; public function __construct($latitude,

    $longitude) { $this->latitude = $latitude; $this->longitude = $longitude; } //getters }
  5. $coordinate = new Coordinate(52.3702157, 4.8951679); $amsterdam = new City("Amsterdam", "Netherlands",

    $coordinate); class City { /** * @var Coordinate */ private $coordinate; //other fields public function __construct( $name, $country, Coordinate $coordinate ) { $this->coordinate = $coordinate; //other assignments } //getters }
  6. $amsterdam = new City( "Amsterdam", "Netherlands", 4.8951679, 52.3702157 ); class

    City { public function __construct( $name, $country, $latitude, $longitude ) { //... } }
  7. class HexColor { private $hexColor; public function __construct($hexColor) { if(!preg_match('/^#?[a-f0-9]{6}$/i',

    $hexColor)) { throw new \InvalidArgumentException(); } $this->hexColor = $hexColor; } public function blend(HexColor $otherHexColor) { $newHexColor = // color blending...; return new HexColor($newHexColor); } }
  8. class User { /** * @var DateTime */ private $registrationDate;

    public function __construct(DateTime $registrationDate) { $this->registrationDate = $registrationDate; } public function getRegistrationDate() { return $this->registrationDate; } } $user = new User(new DateTime("2015-06-26")); if($user->getRegistrationDate()->modify("+1 year") == new DateTime("today")) { //send anniversary gift } $user->getRegistrationDate() == new DateTime("2015-06-26"); //false $user->getRegistrationDate() == new DateTime("2016-06-26"); //true
  9. class User { /** * @var DateTimeImmutable */ private $registrationDate;

    public function __construct(DateTimeImmutable $registrationDate) { $this->registrationDate = $registrationDate; } public function getRegistrationDate() { return $this->registrationDate; } } $user = new User(new DateTimeImmutable("2015-06-26")); if($user->getRegistrationDate()->modify("+1 year") == new DateTimeImmutable("today")) { //send anniversary gift } $user->getRegistrationDate() == new DateTimeImmutable("2015-06-26"); //true
  10. class Money { //fields //constructor //getters public function add(Money $other)

    { if($this->currency != $other->currency) { throw new CurrenciesDontMatch(); } return new Money($this->amount + $other->amount, $this->currency); } }
  11. class DateRange { private $start; private $end; public function __construct(

    DateTimeImmutable $start, DateTimeImmutable $end ) { if($start > $end) { throw new InvalidArgumentException(); } $this->start = $start; $this->end = $end; } //getters } $a = new DateRange(new DateTimeImmutable("today"), new DateTimeImmutable("tomorrow")); $b = new DateRange(new DateTimeImmutable("today"), new DateTimeImmutable("tomorrow")); $c = new DateRange(new DateTimeImmutable("yesterday"), new DateTimeImmutable("today")); $a == $b; //still true $a < $c; //will it work?
  12. class DateRange { private $start; private $end; //constructor //getters /**

    * @return bool */ public function isLessThan(DateRange $other) { return $this->start < $other->start; } } $a = new DateRange(new DateTimeImmutable("today"), new DateTimeImmutable("tomorrow")); $b = new DateRange(new DateTimeImmutable("today"), new DateTimeImmutable("tomorrow")); $c = new DateRange(new DateTimeImmutable("yesterday"), new DateTimeImmutable("today")); $a->isLessThen($b); //false $a->isLessThan($c); //true
  13. class DateRange { private $start; private $end; //constructor //getters //comparation

    public function __toString() { return $this->start->format("U") . " " . $this->end->format("U"); } public static function fromString($string) { if(!preg_match("/^(\S+) (\S+)$/", string, $matches)) { throw new InvalidArgumentException(); } return new DateRange( new DateTimeImmutable($matches[1]), new DateTimeImmutable($matches[2]) ) } }
  14. class DateRange { //... /** * @return DateRange[] */ public

    static function summarize(array $dateRanges) { //some magic to combine overlapping dateranges return $dateRanges; } }
  15. class PersonName { private $firstName; private $nickName; private $lastName; public

    function __construct($firstName, $lastName, $nickName = '') { $this->firstName = $firstName; $this->lastName = $lastName; $this->nickName = $nickName; } //getters public function getDisplayShortName() { return $this->nickName ?: $this->firstName; } public function getDisplayFullName() { return $this->getDisplayShortName() . " " . $this->lastName; } }
  16. $string = " FooBar "; trim($string); //FooBar substr($string, 0, 2);

    //Fo strlen($string); // 2 strtolower($string); //fo //...
  17. class String { public function __construct($string) { /*...*/ } public

    function length() { /*...*/ } public function substring($start, $length) { /*...*/ } public function toLowercase() { /*...*/ } public function trim() { /*...*/ } } $string = new String("foobar"); $string ->trim() ->substring(0, 2) ->toLowercase(); //fo
  18. $weeklyTimeSlot = new WeeklyTimeSlot( WeekDay::friday(), new TimeSlot( new Time(16, 45)

    new Time(17, 30) ) ); /** @var duration Duration */ $duration = $weeklyTimeSlot->getDuration();
  19. class SchoolYear { private $startYear; public function __construct($startYear) { if(!is_int($startYear))

    { throw new InvalidArgumentException(); } $this->startYear = $startYear; } public function getStartYear() { /* ... */ } public function getEndYear() { /* ... */ } public function __toString() { /* ... */ } //2014-2015 }
  20. class SchoolYear { private $startYear; public function __construct($startYear) { /*

    ... */ } public static function current() { /* ... */ } public static function containingDate(DateTimeImmutable $date) { /* ... */ } public static function fromString($string) { /* ... */ } public function next() { /* ... */ } public function previous() { /* ... */ } public function getStartYear() { /* ... */ } public function getEndYear() { /* ... */ } public function __toString() { /* ... */ } public function equals(SchoolYear $schoolYear) { /* ... */ } public function getStartDate() { /* ... */ } public function getEndDate() { /* ... */ } public function getDateRange() { /* ... */ } public function getCalendarWeeks() { /* ... */ } public function startsInWeekend() { /* ... */ } public function isActive() { /* ... */ } public function isPassed() { /* ... */ } public function containsCalendarWeek(CalendarWeek $calendarWeek) { /* ... */ } public function containsDate(DateTimeImmutable $date) { /* ... */ } public function containsDateRange(DateRange $date) { /* ... */ } }
  21. class Talk { //... /** * @ORM\Column(type="datetime") */ private $startTime;

    /** * @ORM\Column(type="datetime") */ private $endTime; public function __construct(/*...*/, TimeSlot $slot) { $this->startTime = $slot->getStartTime(); $this->endTime = $slot->getEndTime(); } /** * @return TimeSlot */ public function getTimeSlot() { return new TimeSlot($this->startTime, $this->endTime); } }
  22. /** * @ORM\Embeddable */ class TimeSlot { /** * @ORM\Column(type="datetime")

    */ private $startTime; /** * @ORM\Column(type="datetime") */ private $endTime; //... }
  23. class Talk { //... /** * @ORM\Embedded(class="TimeSlot") */ private $timeSlot

    public function __construct(/*...*/, TimeSlot $slot) { $this->timeSlot = $timeSlot; } /** * @return TimeSlot */ public function getTimeSlot() { return $this->timeSlot; } //... }
  24. $cars = []; for($i = 0; $i <= 1000000; $i++)

    { $cars[] = new Car("Audi A6", "VIN-NR-2015" . $i, new HexColor("FF0000")); }
  25. $cars = []; for($i = 0; $i <= 1000000; $i++)

    { $cars[] = new Car("Audi A6", "VIN-NR-2015" . $i, HexColor::define("FF0000")); } class HexColor { private $hexColor; private static $hexColors = []; private function __construct($hexColor) { /*...*/ } public static function define($hexColor) { if(!array_key_exists($hexColor, self::$hexColors)) { self::$hexColors[$hexColor] = new self($hexColor); } return self::$hexColors[$hexColor]; } }