OOP To FP

Slides for my talk at Droidcon Berlin 2019

Transcript

1. OOP -> FP droidcon Berlin 2019 1
2. Android @ RedMart 1 Adnan A M droidcon Berlin 2019 2
3. Why is FP hard ? droidcon Berlin 2019 3
4. It isn't ... droidcon Berlin 2019 4
5. Perception vs Reality droidcon Berlin 2019 5
6. Challenge isn't in learning, it's in unlearning ! droidcon Berlin 2019 6
7. What does it mean to be functional ? 4 Declarative/Explicit 4 Immutability/Concurrency 4 Purity 4 Referential Transparency 4 State Isolation droidcon Berlin 2019 7
8. Declarative vs Imperative Imperative -> How ? Declarative -> What ? droidcon Berlin 2019 8
9. Declarative vs Imperative 4 I see an empty table at the end of the room. I and my spouse are going to walk over there and sit down 4 Table for two please droidcon Berlin 2019 9
10. Declarative vs Imperative Imperative focuses on the How val array = listOf(1,2,3,4) var sum = 0 var odds: MutableList<Int> = listOf() for (element in array) { sum += element if (element % 2 == 1) { odds.add(element) } } droidcon Berlin 2019 10
11. Declarative vs Imperative Declarative focuses on the What val array = listOf(1,2,3,4) val sum = array.reduce { sum, i -> sum + i } val odds = array.filter { i -> i % 2 == 1 } droidcon Berlin 2019 11
12. Explicit 4 A function must always have a well defined return type 4 Avoid void/Unit as return types droidcon Berlin 2019 12
13. Explicit fun multiplyBy5(number: Int): Int = { /** Some complex Math **/ } fun asyncCall(callback: CustomListener) = { /** Some IO operation and return via callback **/ } droidcon Berlin 2019 13
14. Immutablity/Concurrency droidcon Berlin 2019 14
15. Immutability/Concurrency droidcon Berlin 2019 15
16. Purity droidcon Berlin 2019 16
17. Pure Functions 4 Produce same output for same inputs 4 Rely only on input parameters 4 Do not have any side effects droidcon Berlin 2019 17
18. Side Effects Modifying anything outside the scope or requiring external context. Examples : 4 Writing to a file/database 4 Making a network request 4 Modifying variables/state droidcon Berlin 2019 18
19. Pure Functions - Sample val z = 10; fun add(x: Int, y: Int): Int { return x + y; } droidcon Berlin 2019 19
20. Pure Functions - Sample Most useful Pure Functions must take at least 1 parameter fun justConstant(): Int { return 1336; } droidcon Berlin 2019 20
21. Pure Functions - Sample Most useful Pure Functions must return a value fun noReturn(x:Int, y:Int) { val z = x + y } droidcon Berlin 2019 21
22. Referential Transparency droidcon Berlin 2019 22
23. Referential Transparency fun referentiallyTransparent(x:Int, y:Int): Int { val z = x + y return z } droidcon Berlin 2019 23
24. Benefits of Pure Functions 4 Unit Testing 4 Paralellization 4 Ordering 4 Memoization droidcon Berlin 2019 24
25. Parallelization Run operations over multiple threads.... Ex: A parallel map implementation can distribute values over multiple threads and collect the results droidcon Berlin 2019 25
26. Ordering fun doSomeWork(array: List<Int>): Work { doWork2(array) doWork1(array) doWork3(array) return Work(doWork1(array)) } droidcon Berlin 2019 26
27. Memoization Since O/P's don't change for same I/P's we can cache and re-use their results droidcon Berlin 2019 27
28. No Side Effects ? droidcon Berlin 2019 28
29. No Side Effects ? Functional Programming doesn't eliminate Side Effects, but contains them and separates them out. droidcon Berlin 2019 29
30. State Isolation Move state modifications to outer boundaries droidcon Berlin 2019 30
31. Function Composition droidcon Berlin 2019 31
32. Exception Handling droidcon Berlin 2019 32
33. Designing a User Profile droidcon Berlin 2019 33
34. User Profile public class User { private String Name; private String email; public String getName() { return Name; } public void setName(String name) { Name = name; } public String getEmail() { return email; } public void setEmail(String email) { this.email = email; } } droidcon Berlin 2019 34
35. Stop Thinking Classes, Start Thinking Functions droidcon Berlin 2019 35
36. FP is not opp of OOP ! Imperative shell on the outside with an FP core on the inside droidcon Berlin 2019 36
37. Making it a habit droidcon Berlin 2019 37
38. # 1 Can this be generic ? droidcon Berlin 2019 38
39. # 2 Make All Things Immutable ! droidcon Berlin 2019 39
40. # 3 Stop using loops droidcon Berlin 2019 40
41. # 4 Stop using if constructs droidcon Berlin 2019 41
42. The 30 Day Challenge No loops No var (Use with caution) No if droidcon Berlin 2019 42
43. Caveats aka How To Not Shoot Yourself In The Foot droidcon Berlin 2019 43
44. # 1 It isn't an all or nothing game ! droidcon Berlin 2019 44
45. # 2 Trying to be over functional droidcon Berlin 2019 45
46. # 3 Learn At Your Own Pace droidcon Berlin 2019 46
47. # 4 Have fun Don't stress it droidcon Berlin 2019 47
48. # 5 Make Your Life Easier droidcon Berlin 2019 48
49. Arrow-Kt droidcon Berlin 2019 49
50. Arrow-Kt Samples droidcon Berlin 2019 50
51. Either Type // Old Exception Style fun parse(s: String): Int = if (s.matches(Regex("-?[0-9]+"))) s.toInt() else throw NumberFormatException("$s is not a valid integer.") // Either Style fun parse(s: String): Either<NumberFormatException, Int> = if (s.matches(Regex("-?[0-9]+"))) Either.Right(s.toInt()) else Either.Left(NumberFormatException("$s is not a valid integer.")) droidcon Berlin 2019 51
52. Either Type val x = parse("2") val value = when(x) { is Either.Left -> when (x.a){ is NumberFormatException -> "Not a number!" else -> "Unknown error" } is Either.Right -> "Got Number: ${x.b}" } droidcon Berlin 2019 52
53. Option Type // Some value contained val someValue: Option<String> = Some("I am wrapped in something") //Empty value val emptyValue: Option<String> = None // Call Site val someValue: Option<Double> = Some(20.0) val value = when(someValue) { is Some -> someValue.t is None -> 0.0 } val number: Option<Int> = Some(3) val noNumber: Option<Int> = None val mappedResult1 = number.map { it * 1.5 } val mappedResult2 = noNumber.map { it * 1.5 } droidcon Berlin 2019 53
54. IO Computation fun getDataFromNetwork(): IO<Either<CustomError, List<User>>> { /** .... **/} IO computation which returns either an error or a list of users droidcon Berlin 2019 54
55. References/Credits 4 47 Degrees - Arrow-kt 4 Charles Scalfani - So You Want To Be A Functional Programmer droidcon Berlin 2019 55
56. May The Functions Be With You ! 4 Reach out to me at @AdnanM0123 4 Talk about OOP/FP or droidcon India or anything Android droidcon Berlin 2019 56