I T.A.K.E. talk: "When DDD meets FP, good things happen"
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Domain-Driven Design (DDD) and Functional Programming (FP) have a lot of good things in common: DDD has borrowed many ideas from the FP community, and both share a common inspiration on established formalisms like maths. For the software developer, the result is a style of code that mixes the best of DDD, OO and FP. Even in non functional languages like Java or C#, this combined set of practices helps craft simple and powerful code that reads well and that is very easy to test. In this talk we will have a closer look at some of these ideas, in the context of domain models inspired from real-world projects. From basic FP hygiene like immutability and closure of operations to more mathematical inspirations from abstract algebra like monoids, we will show how all that translates into beautiful code. WARNING: This may influence your coding style… This talk was presented on the first day of I T.A.K.E. 2013 at Bucharest http://itakeunconf.com/
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I T.A.K.E. talk: "When DDD meets FP, good things happen"
- 1. WHEN FP meets DDD Good Things Happen Cyrille Martraire - @cyriux -
- 5. Arolla.fr
- 6. WARNING The following show features no spectacular stunt, no live coding, only trivial Java code. You can re-create or re-enact at home with no danger.
- 7. A matter of Taste http://rosshirt.blogspot.fr/ The Code Gourmet (dedicate to @ziobrando)
- 8. "My first encounter with FP concepts was from DDD"
- 11. DDD+FP = ?
- 19. I. Putting the model to work II. Building blocks (Tactical DDD) III.Refactoring toward deeper insight IV. Strategic DDD
- 20. Adopted 2005 Still in love
- 22. What do you think when you hear about FP?
- 23. http://jeremykun.com/2013/02/08/why-there-is-no-hitchhikers-guide-to-mathematics-for-programmers/
- 28. No State No War
- 31. What do DDD & FP have in common?
- 33. Learn one and get the other one for FREE!
- 34. DDD FP (OO)
- 35. DDD FP (OO)
- 43. Day Max Temperature Min Temperature Unit (C/F)
- 44. Please compute Daily min-max spreads Daily min-max mids Monthly average ...
- 45. GO
- 47. Read file
- 48. Compute spread & console output
- 50. DONE.
- 51. NEXT
- 55. DONE.
- 56. UH-OH!
- 61. Data access Data access Presentation Presentation Domain Domain Transaction Script 1 Transaction Script 2
- 62. Data access Data access Presentation Presentation Domain Domain Transaction Script 1 Transaction Script 2 ≈
- 63. Data access Data access Presentation Presentation Domain Domain Transaction Script 1 Transaction Script 2 ≈ =
- 64. Data access Data access Presentation Presentation Domain Domain Transaction Script 1 Transaction Script 2 ≈ = =
- 68. Data access Presentation Domain Refactoring of similar Transaction Scripts -> layers!
- 69. Emergence of a domain layer
- 70. Emergence of a domain layer DDD
- 71. Emergence of a domain layer DDD
- 72. Domain layer: "Here we talk about the domain only"
- 73. My hygiene standards in domain layer • Dependencies – Legacy – Middleware – Frameworks – Database stuff – No logging null + TDD, BDD + Clean Code
- 75. Load data process data output data
- 78. Favor side-effect- free functions in domain layer
- 81. side-effect- free function Very easy to test input output
- 83. Side-effect free service <<ValueObje ct <<ValueObje ct <<ValueObject>> <<ValueObje ct <<ValueObject>> <<Service>> <<SPI>><<Service>> <<API>> Values in Values out
- 84. NEXT
- 85. = 1/N ∑
- 86. Varying units
- 87. 18°C + 65°F = ?
- 95. Let’s factor it out
- 97. We can do better
- 98. Extract a TYPE
- 101. Immutable Goodness bugs keep old state safe sharing (concurrency)
- 103. Value Object: equals by fields equality
- 106. FP: everything is a value
- 107. Value Object A DDD pattern to import FP-ish values in OO languages
- 109. “Functional-First” style • Value Objects (Quantity, Range…) as much as possible
- 110. 90% “Functional-First” style Value Objects (Ok, gut feeling, I did’nt measure)
- 112. Methods return same type toCelsius(): Temperature toFarenheit(): Temperature Temperature
- 113. Methods return same type toCelsius(): Temperature toFarenheit(): Temperature Temperature
- 114. avg = 1 ∑ti n i
- 115. double sum = 0; int count = 0; for(Temperature t in temperatures){ sum+= t1.toCelsius().getValue(); count++; } return sum/count;
- 116. double sum = 0; int count = 0; for(Temperature t in temperatures){ sum+= t1.toCelsius().getValue(); count++; } return sum/count;
- 117. DEMETER VIOLATION
- 119. returns a new instance Change -> new instance
- 120. Methods manipulate same type toCelsius(): Temperature toFarenheit(): Temperature add(Temperature): Temperature scale(double): Temperature Temperature
- 123. 18°C + 16°C = 34°C
- 124. Temperature sum = max.add(min); 18°C + 16°C = 34°C
- 125. Object Arithmetics
- 126. Object Arithmetics
- 127. avg = 1 ∑ti n i
- 128. unit-safe
- 129. DONE.
- 133. Zipper?
- 134. We can even do better
- 135. How do domain experts THINK about it?
- 136. How do domain experts THINK about it? SAY SKETCH
- 137. Go out and listen to them!
- 138. Tell us about your domain
- 139. blabla Time Series bla bla...
- 140. Time Series?
- 141. Yes, let me show you
- 142. - = Max Min Spreads
- 143. OK
- 147. Value Object again
- 149. Declarative style TimeSeries spread = max.subtract(min); Temperature sum = max.add(min);
- 150. So far
- 151. Domain Layer
- 152. Better style emerging from refactoring with a focus on the omain
- 153. Wrote code with:
- 154. Wrote code with: no naked primitive
- 155. Wrote code with: no naked primitive no naked collection
- 156. Object Calisthenics?
- 157. Signal to Noise ratio http://www.flickr.com/photos/28471130@N07/2666802097
- 158. Signal to Noise Ratio • SNR ≥ 80 % • Signal (VO): CashFlow.multiply(), CashFlowSequence.add(), .negate(), truncate(), Money.add(), .times (), .opposite(), Fixing, FinancialProduct, BankHolidays, ReferenceData • Noise: CashFlowBuilder, CompositeEngine, ProductFactory, BankHolidaysDecorator
- 161. No worry!
- 164. Just enrich our types label field
- 165. Monad-ish No logging needed Each value stores its history
- 176. In Closing
- 177. Invest time: Learn DDD, and get free FP exposure
- 178. A paradox: FP influence helps craft better Object- Oriented code!
- 179. DDD + FP A love story
- 183. Questions? You can also ask me later! @cyriux
- 184. Merci
- 185. Merci