Value and Record Types

Slides from my talk “Better Domain Models with Value and Record Types.”

Transcript

1. Starring With vs Special Appearances by
4. Java old! C# ABAP PHP Python
5. Kolleg:in gesucht (Deutschlandweit)
6. Buy it on Amazon.com: https://hschwentner.io
7. Photo: Henning Schwentner Let me tell you a story
8. @hschwentner Example: A Banking Domain bank account customer teller computer transaction
10. to deposit to withdraw bank account money amount IBAN to pay interest
11. @hschwentner Example: A Banking Domain computer Banking 3000
13. @hschwentner Software != End in itself
14. @hschwentner ! ! " Software is build Tech people business people # " for for by
16. Software Domain
17. Foto: Rosie the Riveter/Wikimedia/CC-PD-Mark
18. @hschwentner Programming is Model Building
19. @hschwentner Rules of thumb:
20. Objects from real world turn into objects in software
22. Actions from real world turn into operations in software
24. => Object-orientation
25. Object-Oriented Programming Ole-Johan Dahl Photo: Stein Krogdahl, University of Oslo Kristen Nygaard Photo: Jorge Stolfi/Wikipedia !
26. Photo: P. Campbell/Wikipedia Alan Kay Everything is an object "
28. Foto: P. Campbell/Wikipedia James Gosling Everything is an object #
29. Anders Hejlsberg Everything is an object
30. Are those objects?
31. @hschwentner In the real world not everything is an object
32. @hschwentner Domain-Driven Design Eric Evans " Entity Value Object Aggregate Service Factory Repository
33. @hschwentner Entity vs. Value
34. Foto: P. Campbell/Wikipedia James Gosling Everything is an object int short long byte char float double boolean … except:
35. Anders Hejlsberg Everything is an object …except structs
36. Values from real world turn into values in software
38. @hschwentner What is an object/entity?
40. Identity
43. Foto: Th.omas G.Graf/Wikipedia oto: H. Schwentner
44. Grafik: Pixabay
45. Foto: Bernd Schwabe in Hannover/Wikipedia
46. @hschwentner Object: *Identity *Lifecycle *(mutable) state
47. @hschwentner What is a value?
48. Grafik: Public Domain/Pixabay
49. Foto: A. Markiewicz
51. @hschwentner
52. @hschwentner Value: *No identity *immutable
53. @hschwentner Example
54. % & '
56. '
57. ' '
59. % & '
60. ' ' & ' & '
62. Foto: Bibi Saint-Pol/Wikipedia
63. @hschwentner Objects in Languages like Java or C#
69. Foto: Tiia Monto/Wikipedia
76. @hschwentner Identity of an Object
78. 3 3
80. @hschwentner Values in Languages like Java or C#
81. built-in value types primitive types simple types
82. int boolean/bool double char
83. User-defined value types
84. LocalDate/DateTime String
85. object types that behave like value types value-based class (class with) value equality
86. @hschwentner Values in Java
87. int boolean double char
88. unsigned complex
89. iban postcode amount
90. Foto: Public Domain/Pixabay
91. Grafik: Gemeinfrei/Wikipedia
92. value-based class
93. @hschwentner Only final fields
94. @hschwentner No state-changing methods
95. @hschwentner equals() does not depend on identity
96. value-based class <= 13
97. LocalDate String
98. record >= 16
99. record: all fields final field-based equal() [and hashCode()] getters for all fields >= 16
100. value type >= ??
101. @hschwentner Values in C#
102. int bool double char
103. struct <= 7.1
104. @hschwentner Only readonly fields
105. @hschwentner No state-changing methods
106. readonly struct >= 7.2
107. @hschwentner equals() ! == "
108. record <= 9
109. @hschwentner Value equality
110. @hschwentner equals() ! == !
111. @hschwentner Beware: Can be mutable
112. @hschwentner On the heap
113. record struct <= 10
114. @hschwentner Beware: Is mutable
115. readonly record struct <= 10 !
116. @hschwentner Why aren’t int and string enough?
117. @hschwentner Objects/Entities in Java — Example
118. public class Account { }
119. import org.jmolecules.ddd.annotation.Entity; @Entity public class Account { }
120. @Entity public class Account { private int _balance; public int getBalance() { return _balance; } public void setBalance(int balance) { _balance = balance; } } ✘ Bad: The account balance can be set to any value
121. @Entity public class Account { private int _balance; public int balance() { return _balance; } public void deposit(int amount) { _balance += amount; } public void withdraw(int amount) { _balance -= amount; } Better: Operations with domain- specific behavior and names
122. @Entity public class Account { private int _balance; public int balance() { return _balance; } public void deposit(int amount) { _balance += amount; } public void withdraw(int amount) { if (amount > balance()) { throw new IllegalArgumentException("Amount too big"); Even better: Preconditions can be checked
123. @Entity public class Account { // ... public void withdraw(int amount) { assert amount <= balance(); _balance -= amount; } } Assertion using keyword assert
124. GREAT, BUT… @Entity public class Account { // ... public void withdraw(int amount) { assert amount <= balance(); _balance -= amount; } } Can I withdraw a negative amount? In EUR or GBP or…?
125. @hschwentner Values in Java — Example
126. public class Amount { }
127. import org.jmolecules.ddd.annotation.ValueObject; @ValueObject public class Amount { }
128. @ValueObject public class Amount { private int _amount; private Currency _currency; }
129. @ValueObject public class Amount { private final int _amount; private final Currency _currency; }
130. @ValueObject public class Amount { private final int _amount; private final Currency _currency; public Amount(int amount, Currency currency) { _amount = amount; _currency = currency; } }
131. @ValueObject public class Amount { private final int _amount; private final Currency _currency; private Amount(int amount, Currency currency) { _amount = amount; _currency = currency; } public static Amount of(int amount, Currency currency) { return new Amount(amount, currency); } }
132. @ValueObject public class Amount { private final int _amount; private final Currency _currency; public Amount(int amount, Currency currency) { _amount = amount; _currency = currency; } @Override public boolean equals(Object other) { return _amount == ((Amount) other)._amount && _currency.equals(((Amount) other)._currency); }
133. @ValueObject public class Amount { private final int _amount; private final Currency _currency; public Amount(int amount, Currency currency) { _amount = amount; _currency = currency; } @Override public boolean equals(Object other) { return _amount == ((Amount) other)._amount && _currency.equals(((Amount) other)._currency); }
134. @ValueObject public record Amount(int amount, Currency currency) {}
135. @ValueObject public class Amount { private final int _amount; private final Currency _currency; public Amount(int amount, Currency currency) { _amount = amount; _currency = currency; } public Amount add(Amount otherAmount) { return Amount.of(_amount + otherAmount._amount, _currency); } } Der neue Typ hat richtiges fachliches Verhalten
136. @ValueObject public class Amount { private final int _amount; private final Currency _currency; public Amount(int amount, Currency currency) { _amount = amount; _currency = currency; } public Amount add(Amount otherAmount) { assert hasSameCurrency(otherAmount); return Amount.of(_amount + otherAmount._amount, _currency); } … und Verträge, die vor falschen Währungen schützen
137. @ValueObject public record Amount(int amount, Currency currency) { public Amount add(Amount otherAmount) { assert hasSameCurrency(otherAmount); return new Amount(amount + otherAmount.amount(), currency); } public boolean hasSameCurrency(Amount otherAmount) { return otherAmount.currency() == currency; } }
138. @hschwentner Values in C# — Example
139. public class Amount { }
140. using NMolecules.DDD; [ValueObject] public class Amount { }
141. [ValueObject] public class Amount { private readonly int _amount; private readonly Currency _currency; }
142. [ValueObject] public class Amount { private int _amount; private Currency _currency; }
143. [ValueObject] public class Amount { private readonly int _amount; private readonly Currency _currency; public Amount(int amount, Currency currency) { _amount = amount; _currency = currency; } }
144. [ValueObject] public class Amount { private readonly int _amount; private readonly Currency _currency; // ... public override bool Equals(object other) { return other is Amount && _amount == ((Amount) other)._amount && _currency.Equals(((Amount) other)._currency); } }
145. [ValueObject] public class Amount { private readonly int _amount; private readonly Currency _currency; // ... public override bool Equals(object other) => other is Amount && _amount == ((Amount) other)._amount && _currency.Equals(((Amount) other)._currency); }
146. [ValueObject] public class Amount { private readonly int _amount; private readonly Currency _currency; // ... public override bool Equals(object other) => other is Amount && _amount == ((Amount) other)._amount && _currency.Equals(((Amount) other)._currency); // GetHashCode() }
147. [ValueObject] public class Amount { private readonly int _amount; private readonly Currency _currency; // ... public static bool operator ==(Amount a, Amount b) => a.Equals(b); }
148. [ValueObject] public class Amount { private readonly int _amount; private readonly Currency _currency; // ... public static bool operator ==(Amount a, SignDate b) => a.Equals(b); public static bool operator !=(Amount a, SignDate b) => !a.Equals(b); }
152. [ValueObject] public struct Amount { private readonly int _amount; private readonly Currency _currency; public Amount(int amount, Currency currency) { _amount = amount; _currency = currency; } }
153. [ValueObject] public struct Amount { private readonly int _amount; private readonly Currency _currency; public Amount(int amount, Currency currency) { _amount = amount; _currency = currency; } // Equals() does not have to be overridden }
154. [ValueObject] public struct Amount { private readonly int _amount; private readonly Currency _currency; public Amount(int amount, Currency currency) { _amount = amount; _currency = currency; } // but the operators have to be overridden }
155. @hschwentner equals() ! == "
156. [ValueObject] public record Amount(int amount, Currency currency);
157. [ValueObject] public record Amount(int amount, Currency currency); // automatically readonly // Equals(), GetHashCode(), ToString(), operators // do not have to be overloaded and work as expected
158. [ValueObject] public record struct Amount(int amount, Currency currency);
159. [ValueObject] public readonly record struct Amount(int amount, Currency currency);
160. @hschwentner Values in Java — Example continued
161. But
162. 3 3
163. @hschwentner equals() ! == "
166. by value
167. by reference
170. Memory*2
175. int[]
176. 3 5 10 5 0
177. Object[]
178. 3 5 10 5 0
179. 3 10 5 0
180. @hschwentner A Concrete Example
181. @hschwentner LeasingNinja https://leasingninja.io
182. @hschwentner Conclusion
183. @hschwentner Key take aways: *value/object are different *only records yet * value types are still to come (*domain model and performance)
184. Bild: Gemeinfrei
185. @hschwentner Further Reading
186. project valhalla
187. https://domainstorytelling.org
188. Workshop Domain-Driven Design concrete wps.de/ddd
193. Bibliography Beck, Kent et al. Manifesto for Agile Software Development. 2001. Evans, Eric. Domain-Driven Design: Tackling Complexity in the Heart of Software. Boston: Addison-Wesley, 2004. Hofer, Stefan and Henning Schwentner. Domain Storytelling: a Collaborative, Visual, and Agile Way to Develop Domain- Driven Software. Boston: Addison-Wesley, 2022.
195. Henning Schwentner ⌂ https://hschwentner.io @hschwentner hs@wps.de Kolleg:in gesucht (Deutschlandweit)