Immutability to Save an Ever-Changing World

Andrew Cassell
Thursday 18 May 2023 from 11:00 to 12:00
Talk in English - US at php[tek] 2023
Short URL: https://joind.in/talk/ff357

Want to build software that is more testable, easier to modify, and has fewer lines of code? Architecture with more immutable objects that are always in a valid state is the most important lesson I have learned in building better software applications. Using immutable value objects will lead to less checking, fewer bugs, and more DRY code, and will help avoid the “spooky action at a distance” problem in PHP. We will also learn how to use immutable objects and immutable collections to improve design of our mutable entities. Lastly, we’ll see how our immutable modeling approach can drastically reduce the complexity of things in our systems that are mutable.

Transcript

1. Andrew Cassell @alc277 andrewcassell.com Immutability to Save an Ever-Changing World
3. 🍺 Immutability 🍺 Idempotence 🍺 Encapsulation 🍺 Behavior 🍺 Beer
6. Immutability Unchanging over time. Unable to be changed.
7. Alan Kay - The Early History of Small Talk
8. Mutable Object Immutable Object CANNOT Change After Creation CAN Change After Creation
9. Mutable Immutable Read-Only Read & Write
10. $mutableDate = new \DateTime('2023-01-01'); echo $mutableDate->format('Y-m-d H:i:s'); // Outputs "2023-01-01 00:00:00" $newDate = $mutableDate->add(new \DateInterval(‘P14D')); echo $newDate->format('Y-m-d H:i:s'); echo $mutableDate->format('Y-m-d H:i:s'); Mutable
11. $mutableDate = new \DateTime('2023-01-01'); echo $mutableDate->format('Y-m-d H:i:s'); // Outputs "2023-01-01 00:00:00" $newDate = $mutableDate->add(new \DateInterval(‘P14D')); echo $newDate->format('Y-m-d H:i:s'); // Outputs "2023-01-15 00:00:00” echo $mutableDate->format('Y-m-d H:i:s'); Mutable
12. $mutableDate = new \DateTime('2023-01-01'); echo $mutableDate->format('Y-m-d H:i:s'); // Outputs "2023-01-01 00:00:00" $newDate = $mutableDate->add(new \DateInterval(‘P14D')); echo $newDate->format('Y-m-d H:i:s'); // Outputs "2023-01-15 00:00:00” echo $mutableDate->format('Y-m-d H:i:s'); // Outputs "2023-01-15 00:00:00" Mutable
13. $immutableDate = new \DateTimeImmutable('2023-01-01'); echo $immutableDate->format('Y-m-d H:i:s'); // Outputs "2023-01-01 00:00:00" $newDate = $immutableDate->add(new \DateInterval('P14D')); echo $newDate->format('Y-m-d H:i:s'); echo $immutableDate->format('Y-m-d H:i:s'); Immutable
14. $immutableDate = new \DateTimeImmutable('2023-01-01'); echo $immutableDate->format('Y-m-d H:i:s'); // Outputs "2023-01-01 00:00:00" $newDate = $immutableDate->add(new \DateInterval('P14D')); echo $newDate->format('Y-m-d H:i:s'); // Outputs "2023-01-15 00:00:00" echo $immutableDate->format('Y-m-d H:i:s'); Immutable
15. $immutableDate = new \DateTimeImmutable('2023-01-01'); echo $immutableDate->format('Y-m-d H:i:s'); // Outputs "2023-01-01 00:00:00" $newDate = $immutableDate->add(new \DateInterval('P14D')); echo $newDate->format('Y-m-d H:i:s'); // Outputs "2023-01-15 00:00:00" echo $immutableDate->format('Y-m-d H:i:s'); // Outputs "2023-01-01 00:00:00" Immutable
17. Passed in by Reference
18. class BrewSession { private \DateTime $start; public function __construct(\DateTime $start) { $this->start = $start; } public function getStart(): \DateTime { return $this->start; } } $session = new BrewSession(new \DateTime('2023-01-01 15:00')); $brewDate = $session->getStart(); $timeToBottle = $brewDate->add(new \DateInterval('P14D')); echo $session->getStart()->format('Y-m-d H:i:s');
19. } public function getStart(): \DateTime { return $this->start; } } $session = new BrewSession(new \DateTime('2023-01-01 15:00')); $brewDate = $session->getStart(); $timeToBottle = $brewDate->add(new \DateInterval('P14D')); echo $session->getStart()->format('Y-m-d H:i:s');
20. } public function getStart(): \DateTime { return $this->start; } } $session = new BrewSession(new \DateTime('2023-01-01 15:00')); $brewDate = $session->getStart(); $timeToBottle = $brewDate->add(new \DateInterval('P14D')); echo $session->getStart()->format('Y-m-d H:i:s'); // 2023-01-15 15:00:00
21. Spooky Action 
 at a Distance
22. class BrewSession { private \DateTimeImmutable $start; public function __construct(\DateTimeImmutable $start) { $this->start = $start; } public function getStart(): \DateTimeImmutable { return $this->start; } } $session = new BrewSession(new \DateTimeImmutable('2023-01-01 20:00')); $brewDate = $session->getStart(); $timeToBottle = $brewDate->add(new \DateInterval('P14D')); echo $session->getStart()->format('Y-m-d H:i:s'); // Outputs '2023-01-01 20:00:00'
23. public function getStart(): \DateTime { return $this->start; } } $session = new BrewSession(new \DateTime('2023-01-01 15:00’)); $brewDate = clone $session->getStart(); $timeToBottle = $brewDate->add(new \DateInterval('P14D')); echo $session->getStart()->format('Y-m-d H:i:s'); // 2023-01-01 15:00:00 💩
24. Mutable objects depend on state.
25. Mutable objects depend on time.
26. $mutable->function(a,b,c) { global $time; //… } $immutable->function(a,b,c) { //… }
27. $mutable->getValue() { global $time; return $value($time); } $immutable->getValue() { return $value; }
28. My pragmatic summary: A large fraction of the flaws in software development are due to programmers not fully understanding all the possible states their code may execute in.
30. HOW?
31. A small simple object who equality isn’t based on identity Value Objects
33. Plain Old PHP Objects (POPOs)
34. •No setters, all parameters are passed into constructor • Declare all class properties as private • No properties that are mutable objects Immutable Objects
35. RecipeName Example
36. Haystack Needle
40. More Classes
41. Performance & Memory Usage
42. Reflection API
45. // PHP 8.1 class RecipeName { public function __construct(private readonly string $name) { } public function getValue(): string { return $this->name; } }
47. // PHP 8.2 readonly class RecipeName { public string $name; }
48. What should be Immutable?
49. Not Just Static Typing https://github.com/Fiedzia/type-system-research/blob/master/README.md
51. Plain Old PHP Objects (POPOs) • Declare Class Properties as Private • No Setters (behaviors will return new) • No References to Mutable Objects • Throw Exceptions in Constructor Value Objects
52. First Name Last Name Full Name Email Address Recipe Name Date Brewed Recipe ID Temperature Liters Gallons Kilograms Pounds Value Objects
53. Value Objects
55. “Gateway Drug to Test Driven Development” Value Objects
56. “Gateway Drug to Test Driven Development” Value Objects #MYTESTSDONTPASS
57. RecipeName Example
60. cassell:beeriously cassell$ docker run --rm --interactive --tty --network beeriously_default --volume `pwd`:/app --user : --workdir /app beeriously_php-fpm /app/vendor/bin/phpunit --configuration /app/src/Tests/Unit/ phpunit.xml.dist PHPUnit 6.4.3 by Sebastian Bergmann and contributors. FEE 3 / 3 (100%) Time: 2.34 seconds, Memory: 4.00MB There were 2 errors: 1) Beeriously\Tests\Unit\Domain\Recipe\RecipeNameTest::testGetter Error: Class 'Beeriously\Domain\Recipe\RecipeName' not found /app/src/Tests/Unit/Domain/Recipe/RecipeNameTest.php:20 2) Beeriously\Tests\Unit\Domain\Recipe\RecipeNameTest::testToString Error: Class 'Beeriously\Domain\Recipe\RecipeName' not found /app/src/Tests/Unit/Domain/Recipe/RecipeNameTest.php:26 -- There was 1 failure: 1) Beeriously\Tests\Unit\Domain\Recipe\RecipeNameTest::testEmptyFails Failed asserting that exception of type "Error" matches expected exception "Beeriously\Domain\Recipe\InvalidRecipeNameException". Message was: "Class 'Beeriously\Domain\Recipe\RecipeName' not found" at /app/src/Tests/Unit/Domain/Recipe/RecipeNameTest.php:15 . ERRORS! Tests: 3, Assertions: 1, Errors: 2, Failures: 1.
64. cassell:beeriously cassell$ docker run --rm --interactive --tty --network beeriously_default --volume `pwd`:/app --user : --workdir /app beeriously_php-fpm /app/vendor/bin/phpunit --configuration /app/src/Tests/ Unit/phpunit.xml.dist PHPUnit 6.4.3 by Sebastian Bergmann and contributors. ... 3 / 3 (100%) Time: 192 ms, Memory: 4.00MB OK (3 tests, 4 assertions)
65. RecipeName Example 
 PHP 8.1
66. class RecipeName { public function __construct(private readonly string $name) { if (empty(trim($this->name))) { throw new InvalidArgumentException('The recipe name cannot be empty.’); } } public function getName(): string { return $this->name; } }
67. BrewedOn Example
68. class BrewedOn { public function __construct( private readonly DatetimeInterface $datetime ) { if ($this->datetime < new DateTimeImmutable('2023-05-18')) { throw new InvalidArgumentException('The brew date cannot be before May 16, 2023.'); } if ($this->datetime > new DateTimeImmutable(‘2123-05-18')) { throw new InvalidArgumentException('The brew date cannot be that far in the future.'); } } public function getValue(): DatetimeImmutable
69. Pounds Example
70. class Pounds { public function __construct( private float $weight ) { if ($this->weight < 0) { throw new InvalidArgumentException('The weight in pounds must be greater than } } public function asFloat(): float { return $this->weight; } }
71. <?php var_dump(-0.0 > 0); // false var_dump(-0.0 < 0); // false var_dump(-0.0 === 0.0); // true (float) var_dump(-0.0 === 0); // false (int) var_dump(-0.0 == false); // true (bool) var_dump(-0.0 == null); // true (bool) var_dump(-0.0 == “”); // true var_dump(-0.0 == "negativezero"); // true (string)
72. class Pounds { public function __construct( private float $weight ) { if ($this->weight < 0) { throw new InvalidArgumentException('The weight in pounds must be greater than } if($this->weight === -0) { $this->weight = 0; } } public function getAsFloat(): float { return $this->weight; } }
73. Composite Value Objects
74. Full Name First Name + Last Name
75. class FirstName { public function __construct( public readonly string $value, ) { if (empty(trim($this->value))) { throw new InvalidArgumentException("First name cannot be e } } } class LastName { public function __construct( public readonly string $value, ) { if (empty(trim($this->value))) { throw new InvalidArgumentException("Last name cannot be em }
76. class FullName { public function __construct( public readonly FirstName $firstName, public readonly LastName $lastName, ) {} public function getFullName(): string { return $this->firstName->value . ' ' . $this->lastName->value; } } // Usage $firstName = new FirstName("Adolphus"); $lastName = new LastName("Busch"); $fullName = new FullName($firstName, $lastName); echo $fullName->getFullName(); // Output: Adolphus Busch
77. Full Name Salutation + First Name Middle Name(s) + Last Name + Suffix
79. class RecipeUpdatedEmailNotification { public function sendNotification(string $recipeName) { if ($recipeName === "") { throw new \InvalidArgumentException; } // Queue email } }
80. class RecipeUpdatedEmailNotification { public function sendNotification(RecipeName $recipeName) { // Queue email } }
81. Encoding Business Logic in Value Objects
82. class Pounds { public function decreaseBy(Pounds $amount): self { return new self($this->weight - $amount->weight); } public function isGreaterThan(Pounds $b): bool { return $this->weight > $b->weight; } public function toKilograms(): Kilograms { return new Kilograms($this->weight * 0.453592); } }
83. $pounds1 = new Pounds(10); $pounds2 = new Pounds(5); $result = $pounds1->decreaseBy($pounds2);
84. use PHPUnit\Framework\TestCase; class PoundsTest extends TestCase { public function testConstructorThrowsExceptionOnZeroWeight() { $this->expectException(InvalidArgumentException::class); $this->expectExceptionMessage('The weight in pounds must be greater than zero.'); new Pounds(0); } public function testConstructorThrowsExceptionOnNegativeWeight() { $this->expectException(InvalidArgumentException::class); $this->expectExceptionMessage('The weight in pounds must be greater than zero.'); new Pounds(-10); } public function testConstructorSetsWeightToZeroForNegativeZero() { $pounds = new Pounds(-0); $this->assertSame(0.0, $pounds->asFloat());
85. $this->expectExceptionMessage('The weight in pounds must be greater than zero.'); new Pounds(-10); } public function testConstructorSetsWeightToZeroForNegativeZero() { $pounds = new Pounds(-0); $this->assertSame(0.0, $pounds->asFloat()); } public function testDecreaseBy() { $pounds1 = new Pounds(10); $pounds2 = new Pounds(5); $result = $pounds1->decreaseBy($pounds2); $this->assertInstanceOf(Pounds::class, $result); $this->assertSame(5.0, $result->asFloat()); } }
86. $pounds1 = new Pounds(5); $pounds2 = new Pounds(10); $result = $pounds1->decreaseBy($pounds2); class Pounds { public function decreaseBy(Pounds $amount): self { return new self($this->weight - $amount->weight); } }
87. if(!is_numeric($a)) { throw new \Exception(…) } if(!is_numeric($b)) { throw new \Exception(…) } if($a < $b) { throw new \Exception(…) } $pounds = $a - $b;
88. use PHPUnit\Framework\TestCase; class PoundsTest extends TestCase { public function testCantReduceBelowZero() { $this->expectException(InvalidArgumentException::class); $this->expectExceptionMessage('The weight in pounds must be greater $pounds1 = new Pounds(5); $pounds2 = new Pounds(10); $pounds1->decreaseBy($pounds2); } }
89. Natural Language Constructors
90. Natural Language Factory Methods
91. Static Constructors
92. class Pounds { public static function fromKilograms(Kilograms $kilos): Pounds { return new self($kilos->getWeight() * 2.20462); } } class Kilograms { public static function fromPounds(Pounds $lbs): Pounds { return new self($lbs->getWeight() * 0.453592); } }
94. echo abs(-5); // Outputs: 5 echo abs(abs(-5)); // Outputs: 5 echo abs(abs(abs(-5))); // Outputs: 5 Idempotent
95. Value Object No Identity (Only Values) *Immutable Amount Paid Acidity Temperature Entity Identifiable Mutable Lifecycle Contains Value Objects Line Item Brewer Water Chemistry Aggregate Entity Responsible For Child Entities Transaction Boundary Invoice Recipe Brew Session
96. Resist the Urge to Extend
97. class Pounds extends FloatValue { //… }
98. class EmailAddress extends StringObject { //… }
99. Encoding Business Logic in Value Objects
100. Alcohol by Volume
102. Sugar + Yeast = Alcohol + CO 2 C H O ->2C H OH + 2CO 6 12 6 2 5 2
103. Sugar + Yeast = Alcohol + CO2
104. Sugar - Sugar = Alcohol START FINISH
105. Sugar - Sugar = Alcohol START FINISH Volume Volume
106. Hydrometer
107. learntomoonshine.com
108. Michael L. Hall - Zymurgy, Summer 1995, vol. 18, no. 2
110. Calibration Temperature Minimum Gravity Reading Maximum Gravity Reading
137. Immutable Value Objects Typical RecipeName String Temperature Float(7,3) DateBrewed DateTime Gravity Float(7,3) ABV Function + Validation?
138. Entities/Models
139. class User { //☝ properties… public function __construct( Username $username, FullName $fullName, EmailAddress $emailAddress, PasswordHash $hash ) { $this->id = Uuid::uuid4()->toString(); $this->username = $username; $this->fullName = $fullName; $this->emailAddress = $emailAddress; $this->hash = $hash; $this->deleted = false; } } Value Objects Identity
140. class User { //☝ properties… public function __construct( Username $username, FullName $fullName, EmailAddress $emailAddress, PasswordHash $hash ) { $this->id = Uuid::uuid4()->toString(); $this->username = $username; $this->fullName = $fullName; $this->emailAddress = $emailAddress; $this->hash = $hash; $this->deleted = false; } } Immutable
141. SETTERS ARE BAD
146. public static function registerNewBrewer( Username $username, FullName $fullName, EmailAddress $emailAddress, PasswordHash $hash, DateTimeImmutable $now ): self { $user = self::create([ 'id' => (string) Uuid::uuid4(), 'username' => (string) $username, 'full_name' => $fullName->toArray(), 'email_address' => (string) $emailAddress, 'hash' => (string) $hash, ]); $dispatcher->dispatch(new NewUserRegistered($user->getId(), $now)); return $brewer;
147. Immutable “Entity”
154. Immutable Book Mutable Price
155. $price = new Price($book, 15.00) $price->setAmount(16.96); Mutable Immutable $book->setPrice(16.96);
156. $book->setPrice(16.96); $amount = new Amount(16.96, new Currency(‘USD’); $price = new BookPrice($book, $amount); $price->change(new Amount(15.99, new Currency(‘USD’)); Mutable Immutable
157. Events
158. class IngredientAddedToRecipe implements Event { public function __construct( private RecipeId $recipeId, private IngredientId $ingredientId, private IngredientName $ingredientName, private IngredientType $ingredientType, private Pounds $weightInPounds, private DateTimeImmutable $occurredOn ) {}
159. class Recipe { // … public function addIngredient( IngredientId $ingredientId, IngredientName $ingredientName, IngredientType $ingredientType, Pounds $weightInPounds ): void { $this->events[] = new IngredientAddedToRecipe( $this->recipeId, $ingredientId, $ingredientName, $ingredientType, $weightInPounds, new DateTimeImmutable() ); }
160. Immutable Collections
161. npm install immutable
162. <script src="immutable.min.js"></ script> <script> var map1 = Immutable.Map({ a: 1, b: 2, c: 3 }); var map2 = map1.set('b', 50); map1.get('b'); // 2 map2.get('b'); // 50 </script>
163. Speci fi c Gravity Log
165. abstract class ImmutableArray extends SplFixedArray { public function __construct(array $items) { parent::__construct(\count($items)); $i = 0; foreach ($items as $item) { $this->guardType($item); parent::offsetSet($i++, $item); } } abstract protected function guardType($item): void; }
166. class FermentationGravityReadings extends ImmutableArray { public function __construct(array $readings) { parent::__construct($readings); $lastReading = GravityReading::MAX; /** @var GravityReading $reading */ foreach ($readings as $reading) { if ($reading->getValue() > $lastReading) { throw new \InvalidArgumentException; } $lastReading = $reading->getValue(); } } protected function guardType($item) { if (!($item instanceof GravityReading)) { throw new \InvalidArgumentException; } } } Value Object
167. class FermentationGravityReadings extends ImmutableArray { public function __construct(array $readings) { parent::__construct($readings); $lastReading = GravityReading::MAX; /** @var GravityReading $reading */ foreach ($readings as $reading) { if ($reading->getValue() > $lastReading) { throw new \InvalidArgumentException; } $lastReading = $reading->getValue(); } } protected function guardType($item) { if (!($item instanceof GravityReading)) { throw new \InvalidArgumentException; } } } Custom Exception
168. class FermentationGravityReadings extends ImmutableArray { public function __construct(array $readings) { parent::__construct($readings); $lastReading = GravityReading::MAX; /** @var GravityReading $reading */ foreach ($readings as $reading) { if ($reading->getValue() > $lastReading) { throw new \InvalidGravityReadingException; } $lastReading = $reading->getValue(); } } protected function guardType($item) { if (!($item instanceof GravityReading)) { throw new \InvalidArgumentException; } } }
169. class FermentationGravityReadings extends ImmutableArray { public function calculateAbv(): AlcoholByVolume { return new AlcoholByVolume( new GravityRange( $this->first(), $this->last() ) ); } }
170. “Immutable” Collection of Entities
171. Haystack Needle
172. class Grain { public function __construct( GrainName $name, GrainType $grainType, Lovibond $lovibond, DegreesLintner $lintner ) { $this->id = GrainId::newId(); $this->name = $name; $this->grainType = $grainType; $this->lovibond = $lovibond; $this->lintner = $lintner; } }
173. class GrainBill { private Collection $grains; public function __construct(Collection $grains) { $this->grains = $grains; } public function add(MeasuredGrain $grain): void { $this->grains->add($grain); } public function getTotalWeightOfIngredients(): Pounds { $totalWeight = new Pounds(0); foreach ($this->grains as $grain) { $totalWeight = $totalWeight->increaseBy($grain->weightInPounds());
174. public function add(MeasuredGrain $grain): void { $this->grains->add($grain); } public function getTotalWeightOfIngredients(): Pounds { $totalWeight = new Pounds(0); foreach ($this->grains as $grain) { $totalWeight = $totalWeight->increaseBy($grain->weightInPounds()); } return $totalWeight; }
176. class GrainBill { public function doesConvert(): bool { $lintnerPounds = 0; $totalWeight = new Pounds(0); foreach($this->grains as $grain) { $degreesLintner = $grain->getDegreesLintner(); $weight = $grain->getWeightInPounds(); $lintnerPounds += $degreesLintner->asFloat() * $weight->asFloat(); $totalWeight = $totalWeight->add($weight); } $average = new DegreesLintner($lintnerPounds / $totalWeight->asFloat()); return $average->doesConvert(); } }
177. $recipe->addGrain() $recipe->removeGrain() $recipe->updateGrain()
178. $object->create(x) $object->read(x) $object->update(x) $object->delete(x)
179. $object->create(x) { // validate x }
180. $object->read(x) { // validate x }
181. $object->update(x) { // validate x }
182. $object->delete(x) { // validate x }
185. Validate Once Not Validating Transitions Easier to Define the Rules Fewer Moving Parts
187. “Structs”
188. { "recipe": { "name": "Needle Haystack", "style": "Weissbier", "recipeAuthor": "Andy Cassell", "batchSize": 5.0, "boilSize": 6.5, "boilTime": 60, "og": 1.050, "fg": 1.015, "abv": 6.0, "ibu": 10, "color": 12, "fermentables": [ { "name": "American Pilsner", "amount": 4.5, "unit": "lbs" }, { "name": "American Wheat", "amount": 6.5,
189. "color": 12, "fermentables": [ { "name": "American Pilsner", "amount": 4.5, "unit": "lbs" }, { "name": "American Wheat", "amount": 6.5, "unit": "lbs" }, { "name": "American Munich 10L", "amount": 0.5, "unit": "lbs" } ], "hops": [ { "name": "Tettnang", "amount": 1.0, "unit": "oz",
190. ], "hops": [ { "name": "Tettnang", "amount": 1.0, "unit": "oz", "use": "Boil", "time": 60 }, { "name": "Hallertau", "amount": 0.5, "unit": "oz", "use": "Boil", "time": 30 }, { "name": "Tettnang", "amount": 0.5, "unit": "oz", "use": "Flameout" } ]
192. package main import ( "encoding/json" "fmt" "io/ioutil" "os" ) type Recipe struct { Name string `json:"name"` Style string `json:"style"` RecipeAuthor string `json:"recipeAuthor"` BatchSize float64 `json:"batchSize"` BoilSize float64 `json:"boilSize"`
193. type Recipe struct { Name string `json:"name"` Style string `json:"style"` RecipeAuthor string `json:"recipeAuthor"` BatchSize float64 `json:"batchSize"` BoilSize float64 `json:"boilSize"` BoilTime int `json:"boilTime"` OG float64 `json:"og"` FG float64 `json:"fg"` ABV float64 `json:"abv"` IBU int `json:"ibu"` Color int `json:"color"` Fermentables []Fermentables `json:"fermentables"` Hops []Hops `json:"hops"` }
194. } type Fermentables struct { Name string `json:"name"` Amount float64 `json:"amount"` Unit string `json:"unit"` } type Hops struct { Name string `json:"name"` Amount float64 `json:"amount"` Unit string `json:"unit"` Use string `json:"use"` Time int `json:"time"` }
195. var recipe Recipe json.Unmarshal(byteValue, &recipe)
196. class Recipe { // ... existing class definitions ... public static function fromJson(string $json): Recipe { $data = json_decode($json, true); $fermentables = array_map(function($item) { return new Fermentable($item['name'], $item['amount'], $item['unit']); }, $data['fermentables']); $hops = array_map(function($item) { return new Hop($item['name'], $item['amount'], $item['unit'], $item['use'], $item['time']); }, $data['hops']); return new Recipe( new RecipeName($data[‘name’]), $fermentables, $hops ); } }
198. Functional Programming
199. $recipe = new Recipe(//…); $recipe->addThisIngredient(//…); $recipe->addWater(//…); $recipe->addThatIngredient(//…); $recipe->boil(//…); $recipe->getEstimatedABV(); //… === inputs
200. $recipe = new Recipe($history + //…); $recipe->addThisIngredient($history + //…); $recipe->addWater($history + //…); $recipe->addThatIngredient($history + //…); $recipe->boil($history + //…); $recipe->getEstimatedABV($history);
201. From: Glengarry Glen Ross Coffee is for Closures
202. Y-Combinator
203. Y-Combinator
204. Y-Combinator function Y($F) { return function ($n) use ($F) { $g = function ($h) { return function ($x) use ($h) { return $h($h)($x); }; }; return $F($g($g))($n); }; }
206. $brewingProcess = new BrewingProcess([ 'duration' => 15, 'temp' => 115, 'next' => [ 'duration' => 25, 'temp' => 145, 'next' => [ 'duration' => 15, 'temp' => 158, 'next' => [ 'duration' => 5, 'temp' => 172, 'next' => null, ] ] ] ]);
207. class BrewingProcess { public function __construct(private readonly array $mashingSteps) { } public function calculateTotalTime() { $recursiveTimeCalculation = $Y(function ($f) { return function ($step) use ($f) { if ($step === null) { return 0; } $totalTime = $step['duration']; if (isset($step['next'])) { $totalTime += $f($step['next']); } return $totalTime; }; }); $totalTime = 0; foreach ($this->mashingSteps as $step) { $totalTime += $recursiveTimeCalculation($step); } return $totalTime; } }
210. Functional programming with mutable objects is almost impossible to get right
213. Objected Oriented Programming with Immutable Objects
218. ---- MODULE Brewing ---- EXTENDS Naturals, Sequences CONSTANT Steps ASSUME Steps = << "Milling", "Mashing", "Boiling", "Fermenting", "Conditioning", "Packaging", "Drinking" >> VARIABLES process, state (* Define the initial state *) Init == /\ process = Steps[1] /\ state = "Brewing" (* Define the transition from one state to another *)
219. ---- MODULE Brewing ---- EXTENDS Naturals, Sequences CONSTANT Steps ASSUME Steps = << "Milling", "Mashing", "Boiling", "Fermenting", "Conditioning", "Packaging", "Drinking" >> VARIABLES process, state (* Define the initial state *) Init == /\ process = Steps[1] /\ state = "Brewing" (* Define the transition from one state to another *)
220. (* Define the transition from one state to another *) Next == IF process = "Drinking" THEN /\ process' = "Milling" /\ state' = "Drank" ELSE /\ process' = Steps[NextIndex(Steps, process)] /\ state' = "Brewing" (* Define the behavior of the system *) Spec == Init /\ [][Next]_<<process, state>> ====
221. (* Define the behavior of the system *) Spec == Init /\ [][Next]_<<process, state>> ==== NextIndex(S, elem) == LET i == CHOOSE n \in DOMAIN S: S[n] = elem IN IF i = Len(S) THEN 1 ELSE i + 1
225. Final Thoughts
226. homebrewersassociation.org
227. Immutable First