Defensive programming - Speaker Deck

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Tommy Mühle | tommy-muehle.io Defensive programming (with PHP) 1

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Tommy Mühle | tommy-muehle.io Tommy Mühle   Software Engineer and Author 2

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Tommy Mühle | tommy-muehle.io Why defensive programming? 3

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Tommy Mühle | tommy-muehle.io 4

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Tommy Mühle | tommy-muehle.io Defend your code against misuse by others 5

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Tommy Mühle | tommy-muehle.io Let’s go defense 6

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Tommy Mühle | tommy-muehle.io Use PHP7 7

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Tommy Mühle | tommy-muehle.io Scalar type declarations 8

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Tommy Mühle | tommy-muehle.io 9 class Counter { private $count = 0; public function add(int $count) { $this->count += $count; } }

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Tommy Mühle | tommy-muehle.io Return type declarations 10

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Tommy Mühle | tommy-muehle.io 11 class Customer { private $isVerified = false; public function verify() : void { $this->isVerified = true; } public function isVerified() : bool { return $this->isVerified; } }

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Tommy Mühle | tommy-muehle.io declare(strict_types=1); 12

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Tommy Mühle | tommy-muehle.io 13 https:/ /github.com/krakjoe/autostrict

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Tommy Mühle | tommy-muehle.io If you haven’t PHP7 14

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Tommy Mühle | tommy-muehle.io Check parameters by yourself 15

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Tommy Mühle | tommy-muehle.io 16 class Counter { public function add($count) { $this->ensureIsInteger($count); // ... } private function ensureIsInteger($value) { // ... throw new \RuntimeException('...'); } }

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Tommy Mühle | tommy-muehle.io 17 https:/ /github.com/beberlei/assert

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Tommy Mühle | tommy-muehle.io 18 use Assert\Assertion; class Counter { private $count; /** * @param int $count */ public function add($count) { Assertion::integer($count); $this->count += $count; } }

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Tommy Mühle | tommy-muehle.io Options for all versions 19

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Tommy Mühle | tommy-muehle.io Injections only via constructor 20

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Tommy Mühle | tommy-muehle.io 21 class Person { private $address; /** * @param Address $address */ public function __construct(Address $address) { $this->address = $address; } }

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Tommy Mühle | tommy-muehle.io You can also use named constructors 22

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Tommy Mühle | tommy-muehle.io 23 class Person { // ... /** * @param Address $address */ public function __construct(Address $address){ ... } public static function createDetailedPerson( Address $address, Details $details) { $person = new self($address); $person->details = $details; return $person; } }

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Tommy Mühle | tommy-muehle.io Setter for everything 24

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Tommy Mühle | tommy-muehle.io https:/ /speakerdeck.com/ tommymuehle/why-setters-are-bad 25

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Tommy Mühle | tommy-muehle.io Few public methods 26

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Tommy Mühle | tommy-muehle.io Use objects instead of primitives 27

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Tommy Mühle | tommy-muehle.io What? 28

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Tommy Mühle | tommy-muehle.io 29 Avoid primitive types class Person { // ... public function addEmail(string $email) { // ... } public function addAddress(array $address) { // ... } }

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Tommy Mühle | tommy-muehle.io 30 class Person { // ... public function addEmail(EmailAddress $email) { // ... } public function addAddress(Address $address) { // ... } } Use value objects

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Tommy Mühle | tommy-muehle.io 31 final class Email { private $mailbox; private $host; public function __construct(string $email) { if (false === strpos($email, '@')) { throw new \InvalidArgumentException( 'This does not look like an email!'); } list($this->mailbox, $this->host) = explode('@', $email); } public function __toString() { return sprintf('%s@%s', $this->mailbox, $this->host); } }

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Tommy Mühle | tommy-muehle.io Mark classes as ﬁnal 32

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Tommy Mühle | tommy-muehle.io 33 abstract class User { // ... } final class GuestUser extends User { // ... }

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Tommy Mühle | tommy-muehle.io 33 abstract class User { // ... } final class GuestUser extends User { // ... }

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Tommy Mühle | tommy-muehle.io Private properties by default 34

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Tommy Mühle | tommy-muehle.io No uninitialized properties 35

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Tommy Mühle | tommy-muehle.io No mixed properties 36

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Tommy Mühle | tommy-muehle.io Avoid traits if you’re unsure 37

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Tommy Mühle | tommy-muehle.io 38 trait EventGenerator { private $events; public function releaseEvents() { $pendingEvents = $this->events; $this->events = []; return $pendingEvents; } protected function raiseEvent(DomainEvent $event) { $this->events[] = $event; } }

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Tommy Mühle | tommy-muehle.io Extremely defensive 39

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Tommy Mühle | tommy-muehle.io No mixed return types 40

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class Person { private $birthday; /** * @return null|int */ public function getAge() { if (!isset($this->birthday)) { return null; } // Calculate $age ... return $age; } } Tommy Mühle | tommy-muehle.io 41

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Tommy Mühle | tommy-muehle.io 42 class Person { private $birthday; /** * @return int * @throws InvalidArgumentException */ public function getAge() { if (!isset($this->birthday)) { throw new InvalidArgumentException('...'); } // Calculate and return $age ... } public function hasBirthday() { return isset($this->birthday); } }

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Tommy Mühle | tommy-muehle.io You can also use null objects instead 43

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Tommy Mühle | tommy-muehle.io Without null object 44

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Tommy Mühle | tommy-muehle.io 45 final class Order { /** @var Money */ private $price; /** @var Discount */ private $discount; public function getPrice() { $priceWithDiscount = $this->price; if (!$this->discount instanceof Discount) { return $priceWithDiscount; } // ... return new Money($priceWithDiscount); } }

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Tommy Mühle | tommy-muehle.io With null object 46

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Tommy Mühle | tommy-muehle.io 47 interface Amountable { public function getAmount(); } final class HeavyUserDiscount implements Amountable { public function getAmount() { $amount = 0.00; // ... return new Money($amount); } }

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Tommy Mühle | tommy-muehle.io 48 interface Amountable { public function getAmount(); } final class NoDiscount implements Amountable { public function getAmount() { return new Money(0.00); } }

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Tommy Mühle | tommy-muehle.io 49 final class Order { /** @var Money */ private $price; /** @var Discount */ private $discount; public function getPrice() { $amount = $this->price->getAmount() - $this->discount->getAmount(); return new Money($amount); } }

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Tommy Mühle | tommy-muehle.io No optional parameters 50

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class Person { private $address; private $details; public function __construct( Address $address, Details $details = null) { $this->address = $address; $this->details = $details; } } Tommy Mühle | tommy-muehle.io 51

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Tommy Mühle | tommy-muehle.io 52 class Person { private $address; private $details; // ... public function __construct(Address $address) { $this->address = $address; } public function addDetails(Details $details) { $this->details = $details; } }

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Tommy Mühle | tommy-muehle.io Block magic method usage 53

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Tommy Mühle | tommy-muehle.io 54 class Person { // ... public function __clone() { throw new LogicException( 'Why would you even clone me?'); } public function __sleep() { throw new BadMethodCallException( 'Serialize, really?'); } }

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Tommy Mühle | tommy-muehle.io Summary 55

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Tommy Mühle | tommy-muehle.io You can always think diﬀerent 56

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Tommy Mühle | tommy-muehle.io 57 https:/ /laracasts.com/series/php-bits/episodes/1 Visual Debt

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Questions?

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Thank you! Slides http:/ /bit.ly/2qFHyQa Images https:/ /pixabay.com/ @tommy_muehle