Immutability to Save an Ever-Changing World - PHP Benelux 2018

https://conference.phpbenelux.eu/2018/sessions/immutability-to-save-an-ever-changing-world/

Want to build software that is more testable, easier to modify, and has fewer lines of code? Architecting 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, more DRY code, and 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 immutable objects and functional programming can reduce complexity.

Transcript

1. Andrew Cassell @alc277 andrewcassell.com Immutability to Save an Ever-Changing World
7. Immutability & Invariants & Encapsulation & Behavior
8. Good Code?
10. $car->bark(); $dog->drive(); It was not supposed to be about cars barking or dogs driving
12. BEER
14. Immutability & Invariants & Encapsulation & Behavior
16. value Mutable
17. new value Mutable
18. value Immutable
19. value Immutable
20. value Immutable
21. value Immutable
22. value Immutable
23. Mutable Immutable Read-Only Read & Write
33. Passed in by Reference / Pointer
38. Spooky Action at a Distance
46. Mutable objects depend on time.
47. Mutable = Value(t) Immutable = Value()
48. $mutable->function(a,b,c) { global $time; //… }
50. What should be Immutable?
51. Event
52. Event History
53. Request
54. Command
55. Almost Everything
56. HOW?
57. Immutability in PHP
58. Plain Old PHP Objects (POPOs)
59. • POPOs • No setters, all parameters are passed into constructor • Declare all class properties as private • No properties that are mutable objects Immutable Objects in PHP
65. Composite Immutable Objects
75. Reflection API
76. More Classes & Files
77. Performance & Memory Usage
78. Immutability & Invariants & Encapsulation & Behavior
79. Immutability & Invariants & Encapsulation & Behavior
80. OBJECTS FOR ALL THE THINGS
81. Not Just Static Typing https://github.com/Fiedzia/type-system-research/blob/master/README.md
82. Value Objects
84. • POPOs • No setters, all parameters are passed into constructor • Declare all class properties as private • No properties that are mutable objects Immutable Objects in PHP
85. • Immutable Objects • Always in a valid state • Validate in constructor • Behavioral methods return new object Value Objects in PHP
86. Always Valid Value Object Immutable No Identity (Only Values) Recipe Name Weight Temperature Entity Identifiable Mutable Lifecycle Contains Value Objects Line Item Brewer Recipe
87. First Name Last Name Full Name Email Address Recipe Name Date Brewed On Recipe ID Temperature Liters Gallons Kilograms Pounds
88. Value Objects
90. “Gateway Drug to Test Driven Development” Value Objects
91. “Gateway Drug to Test Driven Development” Value Objects #MYTESTSDONTPASS
92. RecipeName Example
96. cassell:beeriously cassell$ 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.
98. 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. .EE 3 / 3 (100%) Time: 1.56 seconds, Memory: 4.00MB There were 2 errors: 1) Beeriously\Tests\Unit\Domain\Recipe\RecipeNameTest::testGetter Error: Call to undefined method Beeriously\Domain\Recipe\RecipeName::getValue() /app/src/Tests/Unit/Domain/Recipe/RecipeNameTest.php:21 2) Beeriously\Tests\Unit\Domain\Recipe\RecipeNameTest::testToString Object of class Beeriously\Domain\Recipe\RecipeName could not be converted to string /app/src/Tests/Unit/Domain/Recipe/RecipeNameTest.php:27 ERRORS! Tests: 3, Assertions: 2, Errors: 2. cassell:beeriously cassell$
100. 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. ..E 2 / 3 (67%) Time: 292 ms, Memory: 4.00MB There was 1 error: 1) Beeriously\Tests\Unit\Domain\Recipe\RecipeNameTest::testToString Object of class Beeriously\Domain\Recipe\RecipeName could not be converted to string /app/src/Tests/Unit/Domain/Recipe/RecipeNameTest.php:27 ERRORS! Tests: 35, Assertions: 78, Errors: 1. make: *** [unit] Error 2 cassell:beeriously cassell$
102. 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)
105. BrewedOn Example
107. Pounds Example
111. <?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 == null); // true (string) var_dump(-0.0 == "negatviezero"); // true (string)
112. Immutability & Invariants & Encapsulation & Behavior
113. Static Constructors
114. Natural Language Constructors
117. Eliminates Checking Value Objects
118. $poundA->reduceBy($poundB);
119. if(!is_numeric($a)) { throw new \Exception(…) } if(!is_numeric($b)) { throw new \Exception(…) } if($a < $b) { throw new \Exception(…) } $pounds = $a - $b;
121. Factories $weight = $factory->create( ‘2 lbs’, $dependency1, $dependency2);
122. Don’t Extend
123. class Pounds extends FloatValue { //… }
124. class EmailAddress extends StringObject { //… }
127. Composite Value Objects
128. Immutability & Invariants & Encapsulation & Behavior
129. Full Name First Name + Last Name
131. Full Name Salutation + First Name Middle Name(s) + Last Name + Suffix
132. Encoding Business Logic in Value Objects
133. Alcohol by Volume
135. Sugar + Yeast = Alcohol + CO 2 C H O ->2C H OH + 2CO 6 12 6 2 5 2
136. Sugar + Yeast = Alcohol + CO2
137. Sugar + Yeast = Alcohol + CO2
138. Sugar - Sugar = Alcohol START FINISH
139. Sugar - Sugar = Alcohol START FINISH Volume Volume
140. Hydrometer
141. learntomoonshine.com
143. Michael L. Hall - Zymurgy, Summer 1995, vol. 18, no. 2
146. Calibration Temperature Minimum Gravity Reading Maximum Gravity Reading
175. Immutable Value Objects Typical RecipeName String Temperature Float(7,3) DateBrewed DateTime Gravity Float(7,3) ABV Function + Validation?
176. Immutability & Invariants & Encapsulation & Behavior
177. Entities
178. Identifiable Have State and are Mutable (Lifecycle) Operate using Value Objects No Security or Permission Checks *(Ideally) Storage Agnostic *(Ideally) Never in an Invalid State Entities
179. BEHAVIOR FIRST! STORAGE SECOND! “Storage Agnostic”
180. SETTERS ARE BAD
185. Calling two setters in a row on the same object Missing a Concept?
186. Calling two methods in a row on the same object Missing a Concept?
187. Passing more than one parameter to a method Missing a Concept?
191. DO AS MUCH AS YOU CAN IN VALUE OBJECTS!
193. Doctrine
196. What is actually an entity?
203. Immutable “Entity”
204. Immutable Book Mutable Price
205. $book->setPrice(16.96); $price = new Price($book) $price->setAmount(16.96); Mutable Immutable
206. $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
207. Immutable Collections
211. Value Object
213. “Immutable” Collection of Entities
224. Functional Programming
225. Procedural Programming
226. $recipe = new Recipe(//…); $recipe->addThisIngredient(//…); $recipe->addWater(//…); $recipe->addThatIngredient(//…); $recipe->boil(//…); $recipe->getEstimatedABV(); //… === inputs
227. $recipe = new Recipe($time + //…); $recipe->addThisIngredient($time + //…); $recipe->addWater($time + //…); $recipe->addThatIngredient($time + //…); $recipe->boil($time + //…); $recipe->getEstimatedABV($time);
228. $recipe = new Recipe($history + //…); $recipe->addThisIngredient($history + //…); $recipe->addWater($history + //…); $recipe->addThatIngredient($history + //…); $recipe->boil($history + //…); $recipe->getEstimatedABV($history);
229. Functional Programming
232. Functional programming with mutable objects is more difficult than with immutable objects.
233. Don’t Do It.
234. Functional Programming?
235. Procedural with Immutable Objects
236. Final Thoughts
238. homebrewersassociation.org
240. PHP BEER BREWING SOFTWARE FOR BITTER DEVELOPERS WHO WANT TO BREW EVEN MORE BITTER BEERS And never heard of not-invented-here and wanna learn and do other good stuff too.
243. Think Immutable First
245. https://www.youtube.com/watch?v=O3T9-FilHVI
247. https://joind.in/talk/aabc8 Thank You!