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
6. Buy it on Amazon.com: https://amzn.to/3nF34nI
8. @hschwentner Software != End in itself
10. Software Domäne
11. Foto: Rosie the Riveter/Wikimedia/CC-PD-Mark
12. @hschwentner Programming is Model Building
13. @hschwentner Rules of thumb:
14. Objects from real world turn into objects in software
15. Actions from real world turn into operations in software
16. => Object-orientation
18. to deposit to withdraw bank account money amount IBAN to pay interest
19. Object-Oriented Programming Ole-Johan Dahl Photo: Stein Krogdahl, University of Oslo Kristen Nygaard Photo: Jorge Stolfi/Wikipedia 🇳🇴‍
20. Photo: P. Campbell/Wikipedia Alan Kay Everything is an object 🇺🇸‍
22. Foto: P. Campbell/Wikipedia James Gosling Everything is an object 🇨🇦‍
23. Anders Hejlsberg Everything is an object
24. @hschwentner In the real world not everything is an object
25. @hschwentner Domain-Driven Design Eric Evans 🇺🇸‍ Entity Value Object Aggregate Service Factory Repository
26. @hschwentner Entity vs. Value
27. Foto: P. Campbell/Wikipedia James Gosling Everything is an object int short long byte char float double boolean … except:
28. Anders Hejlsberg Everything is an object …except structs
29. Values from real world turn into values in software
30. @hschwentner What is an object/entity?
32. Identity
35. Foto: Th.omas G.Graf/Wikipedia oto: H. Schwentner
36. Grafik: Pixabay
37. Foto: Bernd Schwabe in Hannover/Wikipedia
38. @hschwentner Object: *Identity *Lifecycle *(mutable state)
39. @hschwentner What is a value?
40. Grafik: Public Domain/Pixabay
41. Foto: A. Markiewicz
43. @hschwentner
44. @hschwentner Value: *No identity *immutable
45. @hschwentner Example
46. 👬 👭 👫
48. 👫
49. 👫 👫
51. 👬 👭 👫
52. 👫 👫 👭 👫 👭 👫
54. Foto: Bibi Saint-Pol/Wikipedia
55. @hschwentner Objects in Languages like Java or C#
61. Foto: Tiia Monto/Wikipedia
68. 3
69. 3 3
70. 3
71. @hschwentner Where does an object live actually?
79. compile time
81. run time
82. @hschwentner Where does an object live actually?
83. @hschwentner Values in Languages like Java or C#
84. built-in value types primitive types simple types
85. int boolean/bool double char
86. @hschwentner Where does such a value live actually?
87. 3
88. 3 3
90. LocalDate/DateTime String
91. object types that behave like value types value-based class (class with) value equality
92. User-defined value types
93. @hschwentner Values in Java
94. int boolean double char
95. unsigned complex
96. iban postcode amount
97. Foto: Public Domain/Pixabay
98. Grafik: Gemeinfrei/Wikipedia
99. value-based class
100. @hschwentner Only final fields
101. @hschwentner No state-changing methods
102. @hschwentner equals() does not depend on identity
103. value-based class
104. LocalDate String
105. @hschwentner Values in C#
106. int bool double char
107. struct <= 7.1
108. @hschwentner Only readonly fields
109. @hschwentner No state-changing methods
110. readonly struct >= 7.2
111. @hschwentner equals() 👍 == 🙈
112. record <= 9
113. @hschwentner Value equality
114. @hschwentner equals() 👍 == 👍
115. @hschwentner Beware: Can be mutable
116. @hschwentner On the heap
117. record struct <= 10
118. @hschwentner Beware: Is mutable
119. readonly record struct <= 10 😍
120. @hschwentner Why aren’t int and string enough?
121. @hschwentner Values in Java — Example
122. public class Amount { }
123. import org.jmolecules.ddd.annotation.ValueObject; @ValueObject public class Amount { }
124. @ValueObject public class Amount { private int _amount; private Currency _currency; }
125. @ValueObject public class Amount { private final int _amount; private final Currency _currency; }
126. @ValueObject public class Amount { private final int _amount; private final Currency _currency; public Amount(int amount, Currency currency) { _amount = amount; _currency = currency; } }
127. @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); } }
128. @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); }
129. @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); }
130. @ValueObject public record Amount(int amount, Currency currency) {}
131. @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
132. @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
133. @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; } }
134. @hschwentner Values in C# — Example
135. public class Amount { }
136. using NMolecules.DDD; [ValueObject] public class Amount { }
137. [ValueObject] public class Amount { private int _amount; private Currency _currency; }
138. [ValueObject] public class Amount { private readonly int _amount; private readonly Currency _currency; }
139. [ValueObject] public class Amount { private readonly int _amount; private readonly Currency _currency; public Amount(int amount, Currency currency) { _amount = amount; _currency = currency; } }
140. [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); } }
141. [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); }
142. [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() }
143. [ValueObject] public class Amount { private readonly int _amount; private readonly Currency _currency; // ... public static bool operator ==(Amount a, Amount b) => a.Equals(b); }
144. [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); }
146. 3
147. 3
148. [ValueObject] public struct Amount { private readonly int _amount; private readonly Currency _currency; public Amount(int amount, Currency currency) { _amount = amount; _currency = currency; } }
149. [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 }
150. [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 }
151. @hschwentner equals() 👍 == 🙈
152. [ValueObject] public record Amount(int amount, Currency currency);
153. [ValueObject] public record Amount(int amount, Currency currency); // automatically readonly // Equals(), GetHashCode(), ToString(), operators // do not have to be overloaded and work as expected
154. [ValueObject] public record struct Amount(int amount, Currency currency);
155. [ValueObject] public readonly record struct Amount(int amount, Currency currency);
156. @hschwentner !!! If C# jump to Conclusion or Ubiquitous Langague !!!
157. But
158. 3 3
159. @hschwentner equals() 👍 == 🙈
161. 3
162. by value
163. by reference
164. 3
166. Memory*2
167. 3
168. 3
171. int[]
172. 3 5 10 5 0
173. Object[]
174. 3 5 10 5 0
175. 3 10 5 0
176. @hschwentner !!!Ab hier muss es neu!!!
177. @hschwentner The answer
178. Foto: Donald24/Wikipedia
180. @hschwentner “Works like an int – codes like a class”
181. @hschwentner Example
182. y x
183. y x
184. @hschwentner (x, y)
187. Bild: Gemeinfrei
188. Bild: Rursusi/Wikipedia
189. final __ByValue class Point { private final int _x; private final int _y; public Point(int x, int y) { _x = x; _y = y; } public boolean equals(Point other) { return _x == other._x && _y == other._y; } }
190. final __ByValue class Point { private final int _x; private final int _y; public Point(int x, int y) { _x = x; _y = y; } public boolean equals(Point other) { return _x == other._x && _y == other._y; } }
191. final __ByValue class Point { private final int _x; private final int _y; public Point(int x, int y) { _x = x; _y = y; } public boolean equals(Point other) { return _x == other._x && _y == other._y; } }
192. Bild: Rursusi/Wikipedia
193. final __ByValue class Point { private final int _x; private final int _y; public Point(int x, int y) { _x = x; _y = y; } public boolean equals(Point other) { return _x == other._x && _y == other._y; } }
194. final __ByValue class Point { private final int _x; private final int _y; public Point(int x, int y) { _x = x; _y = y; } public boolean equals(Point other) { return _x == other._x && _y == other._y; } }
195. final __ByValue class Point { private final int _x; private final int _y; public Point(int x, int y) { _x = x; _y = y; } public boolean equals(Point other) { return _x == other._x && _y == other._y; } }
196. final __ByValue class Point { private final int _x; private final int _y; public Point(int x, int y) { _x = x; _y = y; } public boolean equals(Point other) { return _x == other._x && _y == other._y; } }
197. final __ByValue class Point { private final int _x; private final int _y; public Point(int x, int y) { _x = x; _y = y; } public boolean equals(Point other) { return _x == other._x && _y == other._y; } }
198. final __ByValue class Point { private final int _x; private final int _y; public Point(int x, int y) { _x = x; _y = y; } public boolean equals(Point other) { return _x == other._x && _y == other._y; } }
199. final __ByValue class Point { private final int _x; private final int _y; public Point(int x, int y) { _x = x; _y = y; } public boolean equals(Point other) { return _x == other._x && _y == other._y; } }
200. @hschwentner “Works like an int – codes like a class”
201. @hschwentner “Works like an int – codes like a class”
202. Point p = __MakeValue(4, 7);
203. Point p = __MakeValue(4, 7);
204. Point p = new Point(4, 7);
205. Point p = Point(4, 7);
206. Point p = (4, 7);
207. 4 7
208. 4 7
211. 4 7
212. 4 7
213. 4 7
216. Point p = __MakeValue Point(4, 7);
217. @hschwentner ==
218. @hschwentner !=
219. Default value
222. @hschwentner What else is there?
223. List<Point>
224. List<int>
225. Grafik: Gemeinfrei/Wikimedia Commons
226. List<Point>
227. @hschwentner Ubiquitous Language?
231. Software != End
233. ?
234. IMPORTANT!
237. ✘
240. Value Object
241. @hschwentner Domain values
242. Postal code GPS coordinate IBAN Container number IATA code Amount
243. Ubiquitous Language
244. Fach- sprache
246. Ludwig Wittgenstein “Whereof one cannot speak, thereof one must be silent”
247. Ludwig Wittgenstein »Wovon man nicht sprechen kann, darüber muss man schweigen.«
248. @hschwentner Example
249. public class BankAccount { private int _balance; public void withdraw(int amount) { _balance -= amount; } // ... }
250. public class BankAccount { private int _balance; public void withdraw(int amount) { _balance -= amount; } // ... }
251. public class BankAccount { private int _balance; public void withdraw(int amount) { _balance -= amount; } // ... }
252. public class BankAccount { private int _balance; public void withdraw(int amount) { _balance -= amount; } // ... }
253. public class BankAccount { private int _balance; public void withdraw(int amount) { _balance -= amount; } // ... }
254. public class BankAccount { private int _balance; private String _currency; public void withdraw(int amount, String currency) { assert currency.equals(_currency); _balance -= amount; } }
255. public class BankAccount { private int _balance; private String _currency; public void withdraw(int amount, String currency) { assert currency.equals(_currency); _balance -= amount; } }
256. public class BankAccount { private int _balance; private String _currency; public void withdraw(int amount, String currency) { assert currency.equals(_currency); _balance -= amount; } }
257. public class BankAccount { private int _balance; private String _currency; public void withdraw(int amount, String currency) { assert currency.equals(_currency); _balance -= amount; } }
258. public class BankAccount { private int _balance; private String _currency; public void withdraw(int amount, String currency) { assert currency.equals(_currency); _balance -= amount; } public void deposit(int amount, String currency) { assert currency.equals(_currency); _balance += amount; } }
259. public class BankAccount { private int _balance; private String _currency; public void withdraw(int amount, String currency) { assert currency.equals(_currency); _balance -= amount; } public void deposit(int amount, String currency) { assert currency.equals(_currency); _balance += amount; } }
260. public class BankAccount { private int _balance; private String _currency; public void withdraw(int amount, String currency) { assert currency.equals(_currency); _balance -= amount; } public void deposit(int amount, String currency) { assert currency.equals(_currency); _balance += amount; } }
261. public class BankAccount { private int _balance; private String _currency; public void withdraw(int amount, String currency) { assert currency.equals(_currency); _balance -= amount; } public void deposit(int amount, String currency) { assert currency.equals(_currency); _balance += amount; } }
262. 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 other) { assert hasSameCurrency(other); return new Amount(_amount + other._amount, _currency); } public boolean hasSameCurrency(Amount other) { return other._currency == _currency; } }
263. 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 other) { assert hasSameCurrency(other); return new Amount(_amount + other._amount, _currency); } public boolean hasSameCurrency(Amount other) { return other._currency == _currency; } }
264. 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 other) { assert hasSameCurrency(other); return new Amount(_amount + other._amount, _currency); } public boolean hasSameCurrency(Amount other) { return other._currency == _currency; } }
265. 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 other) { assert hasSameCurrency(other); return new Amount(_amount + other._amount, _currency); } public boolean hasSameCurrency(Amount other) { return other._currency == _currency; } }
266. 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 other) { assert hasSameCurrency(other); return new Amount(_amount + other._amount, _currency); } public boolean hasSameCurrency(Amount other) { return other._currency == _currency; } }
267. 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 other) { assert hasSameCurrency(other); return new Amount(_amount + other._amount, _currency); } public boolean hasSameCurrency(Amount other) { return other._currency == _currency; } }
268. 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 other) { assert hasSameCurrency(other); return new Amount(_amount + other._amount, _currency); } public boolean hasSameCurrency(Amount other) { return other._currency == _currency; } }
269. public class BankAccount { private Amount _balance; public void withdraw(Amount amount) { _balance.subtract(amount); } public void deposit(Amount amount) { _balance.add(amount); } }
270. public class BankAccount { private Amount _balance; public void withdraw(Amount amount) { _balance.subtract(amount); } public void deposit(Amount amount) { _balance.add(amount); } }
271. public class BankAccount { private Amount _balance; public void withdraw(Amount amount) { _balance.subtract(amount); } public void deposit(Amount amount) { _balance.add(amount); } }
272. public class BankAccount { private Amount _balance; public void withdraw(Amount amount) { assert amount.isGreaterThan(_amount); _balance.subtract(amount); } public void deposit(Amount amount) { _balance.add(amount); } }
273. Memory*2
276. ✘
278. public class Amount { // ... }
279. public __ByValue class Amount { // ... }
280. Bild: Rursusi/Wikipedia
281. public __ByValue class Amount { // ... }
282. @hschwentner eat the cake and have it too
283. @hschwentner real domain models and good performance
284. @hschwentner And in other programming languages?
285. C++
287. Point p;
289. Point p = Point(4, 7);
290. 4 7
291. Point * p_pointer;
293. Point * p_pointer = new Point(4, 7);
294. 4 7
295. Point & p_reference = new Point(4, 7);
296. C++
298. struct
299. 4 7
300. 4 7
304. @hschwentner But
305. @hschwentner Mutable state
306. Foto: Th.omas G.Graf/Wikipedia oto: H. Schwentner
307. Interesting concept: Nullable<T>
309. Scala
310. Case Class
311. @hschwentner Pattern matching
312. @hschwentner Generated equals() based on the members
313. @hschwentner Immutable
314. value-based class
316. Data class
317. @hschwentner In the end
318. @hschwentner Key take aways: *value/object are different *only records yet * value types are still to come (*domain model and performance)
319. Bild: Gemeinfrei
320. @hschwentner Further Reading
321. project valhalla
322. https://domainstorytelling.org
323. Workshop Domain-Driven Design concrete wps.de/ddd
329. Henning Schwentner ⌂ https://hschwentner.io @hschwentner ✉ hs@wps.de
330. @hschwentner 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.