Enumerating behaviour: PHP needs better enum [Berlin, 4. 12. 2018]
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What are possibilities of expressing enumerations in native PHP? And are there better options? Libraries mentioned: - grifart/enum: https://github.com/grifart/enum - consistence/consistence: https://github.com/consistence/consistence/blob/master/docs/Enum/enums.md - myclabs/php-enum: https://github.com/myclabs/php-enum
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Enumerating behaviour: PHP needs better enum [Berlin, 4. 12. 2018]
- 1. Enumeration of values behaviour? Jan Kuchař John Cook honza.kuchar@grifart.cz @honzakuchar
- 2. @honzakuchar keen in domain driven design using static analysis UX community member Jan Kuchař John Cook honza.kuchar@grifart.cz @honzakuchar
- 3. Contents • Story: Project with an order, where state transitions are restricted by domain • Enum in laguages derived from C • What is wrong with C-like implementations? • Better alternatives for PHP
- 7. C C++ C#
- 8. typedef enum { RECEIVED = 1, PROCESSING = 2, FINISHED = 3, CANCELLED = 4 } order_state;
- 9. order_state state = RECEIVED; ✅
- 10. order_state state = 42; compiles " And it should not.
- 12. int + constants in PHP Heritage C enum
- 13. Usage for C-like enum in domain model is limited.
- 14. /** @return int[] */ function nextStates(int $state): array { … }
- 15. 1. type-unsafe (just an integer)
- 16. /** @return int[] */ function nextStates(int $state): array { switch $state { case RECEIVED: return [PROCESSING, CANCELLED]; case … } }
- 17. 2. Domain logic spreads all over application.
- 18. /** @return int[] */ function nextStates(int $state): array { switch $state { case … } } default: throw new UnexpectedState();
- 19. 3. Does not validate its values. So you have to - every time you use a value.
- 20. Usage for C-like enum in domain model is limited. ❌ does not validate values ❌ is not type safe ❌ does not keep behaviour in one place
- 21. SplEnum, class constants 🙈class State { public const RECEIVED = 1; public const PREPARING = 2; … } The same problem again!
- 22. Custom enum implementations to the rescue. ✚
- 23. @honzakuchar final class OrderState extends Enum { public const RECEIVED = 'received', PROCESSING = 'processing', … function nextPossibleStates(OrderState $state) { // ... }
- 24. composer require myclabs/php-enum ✅ type safe ✅ simple behaviours
- 25. @honzakuchar
- 26. composer require consistence/consistence + multi enums ✅ type safe ✅ simple behaviour ✅ can compare instances
- 28. @honzakuchar final class OrderState { public const RECEIVED = 'received'; public const PROCESSING = 'processing'; public const FINISHED = 'finished'; public const CANCELLED = 'cancelled'; }
- 29. @honzakuchar function canDoTransition(string $currentState, string $desiredState): bool { switch ($currentState) { case OrderState::RECEIVED: return $desiredState === OrderState::PROCESSING || $desiredState === OrderState::CANCELLED; case … global function
- 30. Make it type safe
- 31. @honzakuchar /** * @method static OrderState RECEIVED() * @method static OrderState PROCESSING() * … */ final class OrderState extends Enum { protected const RECEIVED = 'received', PROCESSING = 'processing', …; }
- 32. @honzakuchar
- 33. @honzakuchar function canDoTransition( string $currentState, string $desiredState ): bool function canDoTransition( OrderState $currentState, OrderState $desiredState ): bool
- 35. @honzakuchar final class OrderState extends Enum { protected const RECEIVED = 'received', PROCESSING = 'processing', … public function canDoTransition(OrderState $desiredState): bool { if ($this === self::RECEIVED()) { return $desiredState === self::PROCESSING() || …; } function canDoTransition( OrderState $currentState, OrderState $desiredState ): bool { … } global function
- 38. @honzakuchar final class OrderState extends Enum { protected const RECEIVED = 'received', PROCESSING = 'processing', … public function canDoTransition(OrderState $desiredState): bool { if ($this === self::RECEIVED()) { return $desiredState === self::PROCESSING() || …; } … throw new LogicException('Should not happen: Unknown state'); } ❌ There are still ugly ifs which are hard to read.
- 39. @honzakuchar final class OrderState extends Enum { protected const RECEIVED = 'received', PROCESSING = 'processing', … public function canDoTransition(OrderState $desiredState): bool { if ($this === self::RECEIVED()) { return $desiredState === self::PROCESSING() || …; } … throw new LogicException('Should not happen: Unknown state'); } ❌ I have to worry about case when someone adds new value to this enum and forgets to add switch case.
- 40. Lets fix this using composition
- 41. @honzakuchar abstract class OrderState extends Enum { protected const RECEIVED = 'received', PROCESSING = ‚processing‘ …; abstract public function canDoTransition(OrderState $nextState): bool;
- 42. @honzakuchar abstract class OrderState extends Enum {
- 43. @honzakuchar
- 44. @honzakuchar ✅ Now type-system knows that every enum value must have method canDoTransition().
- 45. @honzakuchar ✅ Got rid of all ifs and switches.
- 46. @honzakuchar ✅ Public API haven’t changed from previous example.
- 47. composer require grifart/enum github.com/grifart/enum ✅ type safe ✅ can compare instances ✅ behaviour by composition POLYMORHISM? checking of annotations
- 49. Jan Kuchař John Cook reach me at: honza.kuchar@grifart.cz @honzakuchar