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, 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 immutable objects and functional programming can reduce complexity.

Transcript

1. Andrew Cassell @alc277 andrewcassell.com Immutability to Save an Ever-Changing World
5. Immutability & Invariants & Encapsulation & Behavior
6. Good Code?
9. $car->bark(); $dog->drive(); It was not supposed to be about cars barking or dogs driving
11. BEER
12. Immutability & Invariants & Encapsulation & Behavior
13. Mutable Immutable Read-Only After Creation Read & Write
23. Passed in by Reference / Pointer
28. Spooky Action at a Distance
35. Mutable objects depend on time.
36. Mutable = Value(t) Immutable = Value()
37. $mutable->function(a,b,c) { global $time; //… }
39. What should be Immutable?
40. Event
41. Event History
42. Request
43. Response
44. Command
45. Almost Everything
46. HOW?
47. Immutability in PHP
48. Plain Old PHP Objects (POPOs)
49. • POPOs • No setters, all parameters are passed into constructor • Declare all class properties as private • No properties that are mutable objects Immutable Objects in PHP
55. Composite Immutable Objects
65. Reflection API
66. More Classes & Files
67. Performance & Memory Usage
68. Immutability & Invariants & Encapsulation & Behavior
69. Immutability & Invariants & Encapsulation & Behavior
70. OBJECTS FOR ALL THE THINGS
71. Not Just Static Typing https://github.com/Fiedzia/type-system-research/blob/master/README.md
72. Value Objects
74. • POPOs • No setters, all parameters are passed into constructor • Declare all class properties as private • No properties that are mutable objects Immutable Objects in PHP
75. • Immutable Objects • Always in a valid state • Validate in constructor • Behavioral methods return new object • Not dependencies Value Objects in PHP
76. Always Valid Value Object Immutable No Identity (Only Values) Recipe Name Weight Temperature Entity Identifiable Mutable Lifecycle Contains Value Objects Line Item Brewer Recipe
77. First Name Last Name Full Name Email Address Recipe Name Date Brewed On Recipe ID Temperature Liters Gallons Kilograms Pounds Value Objects
78. Value Objects
80. “Gateway Drug to Test Driven Development” Value Objects
81. “Gateway Drug to Test Driven Development” Value Objects #MYTESTSDONTPASS
82. RecipeName Example
85. cassell:beeriously cassell$ 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.
89. 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)
91. BrewedOn Example
93. Pounds Example
97. <?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 == "negativezero"); // true (string)
98. Immutability & Invariants & Encapsulation & Behavior
99. Eliminate Checking Value Objects
105. Static Constructors
106. Natural Language Constructors
109. Immutability & Invariants & Encapsulation & Behavior
111. $poundsA->reduceBy($poundsB);
112. if(!is_numeric($a)) { throw new \Exception(…) } if(!is_numeric($b)) { throw new \Exception(…) } if($a < $b) { throw new \Exception(…) } $pounds = $a - $b;
113. Don’t Extend
114. class Pounds extends FloatValue { //… }
115. class EmailAddress extends StringObject { //… }
118. Composite Value Objects
119. Immutability & Invariants & Encapsulation & Behavior
120. Full Name First Name + Last Name
122. Full Name Salutation + First Name Middle Name(s) + Last Name + Suffix
123. Encoding Business Logic in Value Objects
124. Alcohol by Volume
126. Sugar + Yeast = Alcohol + CO 2 C H O ->2C H OH + 2CO 6 12 6 2 5 2
127. Sugar + Yeast = Alcohol + CO2
128. Sugar - Sugar = Alcohol START FINISH
129. Sugar - Sugar = Alcohol START FINISH Volume Volume
130. Hydrometer
131. learntomoonshine.com
132. Michael L. Hall - Zymurgy, Summer 1995, vol. 18, no. 2
134. Calibration Temperature Minimum Gravity Reading Maximum Gravity Reading
159. Immutable Value Objects Typical RecipeName String Temperature Float(7,3) DateBrewed DateTime Gravity Float(7,3) ABV Function + Validation?
160. Immutability & Invariants & Encapsulation & Behavior
161. Entities
162. Identifiable Have State and are Mutable (Lifecycle) Operate using Value Objects *(Ideally) Storage Agnostic *(Ideally) Never in an Invalid State Entities
165. BEHAVIOR FIRST! STORAGE SECOND! “Storage Agnostic”
166. SETTERS ARE BAD
171. Calling two setters in a row on the same object Missing a Concept?
172. Calling two methods in a row on the same object Missing a Concept?
173. Passing more than one parameter to a method Missing a Concept?
177. DO AS MUCH AS YOU CAN IN VALUE OBJECTS!
179. Doctrine
188. What is actually an entity?
196. Immutable “Entity”
197. Immutable Book Mutable Price
198. $book->setPrice(16.96); $price = new Price($book,15.00) $price->setAmount(16.96); Mutable Immutable
199. $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
200. Immutable Collections
204. Value Object
206. “Immutable” Collection of Entities
218. Functional Programming
219. Procedural Programming
220. $recipe = new Recipe(//…); $recipe->addThisIngredient(//…); $recipe->addWater(//…); $recipe->addThatIngredient(//…); $recipe->boil(//…); $recipe->getEstimatedABV(); //… === inputs
221. $recipe = new Recipe($time + //…); $recipe->addThisIngredient($time + //…); $recipe->addWater($time + //…); $recipe->addThatIngredient($time + //…); $recipe->boil($time + //…); $recipe->getEstimatedABV($time);
222. $recipe = new Recipe($history + //…); $recipe->addThisIngredient($history + //…); $recipe->addWater($history + //…); $recipe->addThatIngredient($history + //…); $recipe->boil($history + //…); $recipe->getEstimatedABV($history);
223. Functional Programming
226. Functional programming with mutable objects is more difficult than with immutable objects.
227. Don’t Do It.
228. Functional Programming?
229. Procedural with Immutable Objects
230. Objected Oriented Programming with Immutable Objects
231. Final Thoughts
233. homebrewersassociation.org
235. 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.
239. https://www.youtube.com/watch?v=O3T9-FilHVI
241. Think Immutable First
242. https://joind.in/talk/aabc8 Thank You! @alc277