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
   

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5. Immutability &
   Invariants &
   Encapsulation &
   Behavior
   

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6. Good
   Code?
   

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9. $car->bark();
   $dog->drive();
   It was not supposed to be about cars barking or dogs driving
   

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11. BEER
    

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12. Immutability &
    Invariants &
    Encapsulation &
    Behavior
    

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13. Mutable
    Immutable
    Read-Only
    After Creation
    Read & Write
    

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23. Passed in by
    Reference /
    Pointer
    

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28. Spooky
    Action at a
    Distance
    

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35. Mutable objects
    depend on time.
    

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36. Mutable = Value(t)
    Immutable = Value()
    

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37. $mutable->function(a,b,c) {
    global $time;
    //…
    }
    

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39. What should be
    Immutable?
    

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40. Event
    

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41. Event History
    

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42. Request
    

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43. Response
    

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44. Command
    

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45. Almost
    Everything
    

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46. HOW?
    

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47. Immutability
    in PHP
    

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48. Plain Old PHP Objects
    (POPOs)
    

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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
    

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55. Composite
    Immutable
    Objects
    

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65. Reflection
    API
    

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66. More
    Classes &
    Files
    

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67. Performance &
    Memory Usage
    

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68. Immutability &
    Invariants &
    Encapsulation &
    Behavior
    

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69. Immutability &
    Invariants &
    Encapsulation &
    Behavior
    

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70. OBJECTS FOR
    ALL THE THINGS
    

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71. Not Just
    Static Typing
    https://github.com/Fiedzia/type-system-research/blob/master/README.md
    

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72. Value
    Objects
    

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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
    

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75. • Immutable Objects
    • Always in a valid state
    • Validate in constructor
    • Behavioral methods return new object
    • Not dependencies
    Value Objects in PHP
    

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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
    

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77. First Name
    Last Name
    Full Name
    Email Address
    Recipe Name
    Date Brewed On
    Recipe ID
    Temperature
    Liters
    Gallons
    Kilograms
    Pounds
    Value Objects
    

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78. Value Objects
    

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80. “Gateway Drug to
    Test Driven Development”
    Value Objects
    

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81. “Gateway Drug to
    Test Driven Development”
    Value Objects
    #MYTESTSDONTPASS
    

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82. RecipeName
    Example
    

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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.
    

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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)
    

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91. BrewedOn
    Example
    

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93. Pounds
    Example
    

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97. 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)
    

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98. Immutability &
    Invariants &
    Encapsulation &
    Behavior
    

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99. Eliminate Checking
    Value Objects
    

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105. Static
     Constructors
     

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106. Natural
     Language
     Constructors
     

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109. Immutability &
     Invariants &
     Encapsulation &
     Behavior
     

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111. $poundsA->reduceBy($poundsB);
     

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112. if(!is_numeric($a)) {
     throw new \Exception(…)
     }
     if(!is_numeric($b)) {
     throw new \Exception(…)
     }
     if($a < $b) {
     throw new \Exception(…)
     }
     $pounds = $a - $b;
     

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113. Don’t Extend
     

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114. class Pounds extends FloatValue
     {
     //…
     }
     

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115. class EmailAddress extends StringObject
     {
     //…
     }
     

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118. Composite
     Value Objects
     

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119. Immutability &
     Invariants &
     Encapsulation &
     Behavior
     

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120. Full Name
     First Name + Last Name
     

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122. Full Name
     Salutation + First Name
     Middle Name(s) +
     Last Name + Suffix
     

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123. Encoding
     Business Logic in
     Value Objects
     

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124. Alcohol by
     Volume
     

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126. Sugar + Yeast =
     Alcohol + CO
     2
     C H O ->2C H OH + 2CO
     6 12 6 2 5 2
     

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127. Sugar + Yeast =
     Alcohol + CO2
     

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128. Sugar - Sugar = Alcohol
     START FINISH
     

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129. Sugar - Sugar = Alcohol
     START FINISH
     Volume
     Volume
     

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130. Hydrometer
     

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131. learntomoonshine.com
     

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132. Michael L. Hall - Zymurgy, Summer 1995, vol. 18, no. 2
     

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134. Calibration Temperature
     Minimum Gravity Reading
     Maximum Gravity Reading
     

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159. Immutable Value Objects Typical
     RecipeName String
     Temperature Float(7,3)
     DateBrewed DateTime
     Gravity Float(7,3)
     ABV Function + Validation?
     

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160. Immutability &
     Invariants &
     Encapsulation &
     Behavior
     

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161. Entities
     

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162. Identifiable
     Have State and are Mutable (Lifecycle)
     Operate using Value Objects
     *(Ideally) Storage Agnostic
     *(Ideally) Never in an Invalid State
     Entities
     

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165. BEHAVIOR FIRST!
     STORAGE SECOND!
     “Storage Agnostic”
     

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166. SETTERS
     ARE BAD
     

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171. Calling two setters in a row
     on the same object
     Missing a Concept?
     

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172. Calling two methods in a row
     on the same object
     Missing a Concept?
     

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173. Passing more than one
     parameter to a method
     Missing a Concept?
     

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177. DO AS MUCH AS
     YOU CAN IN
     VALUE OBJECTS!
     

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179. Doctrine
     

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188. What is actually
     an entity?
     

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196. Immutable
     “Entity”
     

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197. Immutable
     Book
     Mutable
     Price
     

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198. $book->setPrice(16.96);
     $price = new Price($book,15.00)
     $price->setAmount(16.96);
     Mutable
     Immutable
     

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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
     

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200. Immutable
     Collections
     

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204. Value Object
     

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206. “Immutable”
     Collection
     of Entities
     

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218. Functional
     Programming
     

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219. Procedural
     Programming
     

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220. $recipe = new Recipe(//…);
     $recipe->addThisIngredient(//…);
     $recipe->addWater(//…);
     $recipe->addThatIngredient(//…);
     $recipe->boil(//…);
     $recipe->getEstimatedABV();
     //… === inputs
     

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221. $recipe = new Recipe($time + //…);
     $recipe->addThisIngredient($time + //…);
     $recipe->addWater($time + //…);
     $recipe->addThatIngredient($time + //…);
     $recipe->boil($time + //…);
     $recipe->getEstimatedABV($time);
     

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222. $recipe = new Recipe($history + //…);
     $recipe->addThisIngredient($history + //…);
     $recipe->addWater($history + //…);
     $recipe->addThatIngredient($history + //…);
     $recipe->boil($history + //…);
     $recipe->getEstimatedABV($history);
     

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223. Functional
     Programming
     

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226. Functional programming with
     mutable objects is more difficult
     than with immutable objects.
     

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227. Don’t Do It.
     

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228. Functional
     Programming?
     

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229. Procedural with
     Immutable
     Objects
     

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230. Objected Oriented
     Programming with
     Immutable Objects
     

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231. Final Thoughts
     

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233. homebrewersassociation.org
     

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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.
     

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239. https://www.youtube.com/watch?v=O3T9-FilHVI
     

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241. Think
     Immutable
     First
     

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242. https://joind.in/talk/aabc8
     Thank You!
     @alc277
     

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