dotnetMalaga_2022_Functional_Programming.pdf

Transcript

1. CONFIDENTIAL. Copyright © 1 Functional programming in C#, Is it possible? N o v 2 0 2 2
2. CONFIDENTIAL. Copyright © 2 Who am I? • 21 years of experience • Played different roles in Software Building (developer, team lead, architect, engineering director) • Currently Chief Software Engineer at • Also, Key developer at
3. CONFIDENTIAL. Copyright © 3 What’s the fuzz about Functional programming?
4. CONFIDENTIAL. Copyright © 4 CONFIDENTIAL. Copyright © 4 • Deterministic • Immutable(Does not change state or parameters) • Can live without context • Functions as first class values
5. CONFIDENTIAL. Copyright © 5 CONFIDENTIAL. Copyright © 5 BENEFITS Easier to test Better readability More compact code Thread-safe by default Paralelizable out of the box
6. CONFIDENTIAL. Copyright © 6 Tools Lambda Tuples Deconstruction Records Immutability LINQ
7. CONFIDENTIAL. Copyright © 7 Lambda
8. CONFIDENTIAL. Copyright © 8 Tuples
9. CONFIDENTIAL. Copyright © 9 Deconstruction
10. CONFIDENTIAL. Copyright © 10 Records
11. CONFIDENTIAL. Copyright © 11 Immutability
12. CONFIDENTIAL. Copyright © 12 LINQ
13. CONFIDENTIAL. Copyright © 13 CONFIDENTIAL. Copyright © 13 What is a “pure” function? Output depends on inputs Cause no side effects Can live in the “void”
14. CONFIDENTIAL. Copyright © 14 CONFIDENTIAL. Copyright © 14 What is a “side effect”? Mutates global state Mutates input args Modify I/O Invoke external services Throw exceptions
15. CONFIDENTIAL. Copyright © 15 CONFIDENTIAL. Copyright © 15 So, are “impure” functions bad? In Mutates global state Mutates input args Modify I/O Invoke external services Throw exceptions AVOID! ISOLATE
16. CONFIDENTIAL. Copyright © 16 Functions as first-class citizens
17. CONFIDENTIAL. Copyright © 17 CONFIDENTIAL. Copyright © 17 “Honest” functions, you say? It returns a value of the declared type It doesn’t throw exceptions It never returns null
18. CONFIDENTIAL. Copyright © 18 Dishonest function
19. CONFIDENTIAL. Copyright © 19 Honest function
20. CONFIDENTIAL. Copyright © 20 Why null is dangerous Pollutes mathematical models, example: - Age has 120 possible values - If we add null as possible value, we will have 121 - If we combine with Gender (2 values + null) - We could have 243 possible values! We need to deal with all these cases Ambiguous function signatures Reference types are nullable and struct types are not Defensive null-checking - In case an unexpected null is found, what should we do?
21. CONFIDENTIAL. Copyright © 21 CONFIDENTIAL. Copyright © 21 Can we get rid of the infamous “Object reference not set to an instance of an object”? Note: I’m going to use LaYumba library for the following examples https://github.com/la-yumba/functional-csharp-code
22. CONFIDENTIAL. Copyright © 22 YOU DON’T GET THIS EXCEPTION IF YOU DON’T USE NULLS!
23. CONFIDENTIAL. Copyright © 23
24. CONFIDENTIAL. Copyright © 24 CONFIDENTIAL. Copyright © 24 Main functional programming patterns NERD ALERT!
25. CONFIDENTIAL. Copyright © 25 MAP
26. CONFIDENTIAL. Copyright © 26 FOREACH
27. CONFIDENTIAL. Copyright © 27 BIND
28. CONFIDENTIAL. Copyright © 28 RETURN
29. CONFIDENTIAL. Copyright © 29 CONFIDENTIAL. Copyright © 29 And finally …
30. CONFIDENTIAL. Copyright © 30 FUNCTOR is … MONAD is … a M<T> that has a Map type function a M<T> that has both, a Bind and a Return type functions … Therefore, IEnumerable<T> is both a Functor and a Monad!!! BONUS: Task<T> is too
31. CONFIDENTIAL. Copyright © 31 So, at the end, is this true?
32. CONFIDENTIAL. Copyright © 32 Normally no if, for, try or catch statements A bunch of one- liners More condensed code Pipe.lining()
33. CONFIDENTIAL. Copyright © 33 Thank you! Credits to Functional Programming in C# book by Enrico Buonanno.