Deep Dive Into Pattern Matching & Destructuring

Pattern Matching and Destructuring are two simple, yet powerful features in functional programming languages. There are several ways we can leverage them to make cleaner code. It also encourages you to think data as a first-class citizen and provide the essential tooling.

In this session, we are going to learn what these techniques bring to the table by looking at some real-world use-cases in Kotlin & Clojure.

Transcript

1. Lead Consultant www.ajira.tech Tamizhvendan S Passionate, Pragmatic and Polyglot Programmer https://www.demystifyfp.com tamizhvendan Deep Dive Into Pattern Matching And Destructuring
2. Pattern Matching And Destructuring It’s not new!
3. val texts = arrayOf( "The flight arrived at 12734722.", "The meeting starts at 20730700." ) texts.forEach { printTimestamp(it) } Hour: 12, Minute: 34, Second: 22 Hour: 20, Minute: 30, Second: 00
4. fun printTimestamp(text : String) { val atIndex = text.indexOf("at") val timestamp = text .subSequence(atIndex + 3, atIndex + 11) .split(':') val hour = timestamp[0] val minute = timestamp[1] val second = timestamp[2] println("Hour: $hour, Minute: $minute, Second: $second") } A Naive Approach
5. A Naive Approach fun printTimestamp(text : String) { val atIndex = text.indexOf("at") val timestamp = text .subSequence(atIndex + 3, atIndex + 11) .split(':') val hour = timestamp[0] val minute = timestamp[1] val second = timestamp[2] println("Hour: $hour, Minute: $minute, Second: $second") }
6. Regex to the Rescue fun printTimestamp(text : String) { val pattern = "(\\d\\d)7(\\d\\d)7(\\d\\d)" val regex = pattern.toRegex() val timestamp = regex.find(text)UUVgroupValues val hour = timestamp[1] val minute = timestamp[2] val second = timestamp[3] println("Hour: $hour, Minute: $minute, Second: $second") }
7. Pattern Made The Difference fun printTimestamp(text : String) { val pattern = "(\\d\\d)7(\\d\\d)7(\\d\\d)" val regex = pattern.toRegex() val timestamp = regex.find(text)UUVgroupValues val hour = timestamp[1] val minute = timestamp[2] val second = timestamp[3] println("Hour: $hour, Minute: $minute, Second: $second") }
8. Pattern Matching And Destructuring is not limited to “string” alone
9. Pattern Matching And Destructuring can be applied to “data”
10. Representing Data
11. Primitives & Collections 42, 3.14, "Lorum Ipsum", true
12. Primitives & Collections 42, 3.14, "Lorum Ipsum", true [0, 1, 42]
13. Primitives & Collections 42, 3.14, "Lorum Ipsum", true [0, 1, 42] {"firstName" : "John", "lastName" : "Doe"}
14. Representing Data Using Primitives val timestamp = arrayOf(12, 34, 22)
15. Representing Data Using Primitives val timestamp = arrayOf(12, 34, 22) hour
16. Representing Data Using Primitives val timestamp = arrayOf(12, 34, 22) hour minute
17. Representing Data Using Primitives val timestamp = arrayOf(12, 34, 22) hour minute second
18. Representing Data Using Objects import java.time.LocalTime; class Program { public static void main(String[] args) { LocalTime timestamp = LocalTime.of(12, 34, 22); int hour = timestamp.getHour(); int minute = timestamp.getMinute(); int second = timestamp.getSecond(); System.out.println(timestamp); } }
19. Guess the output import java.time.LocalTime; class Program { public static void main(String[] args) { LocalTime t1 = LocalTime.of(12, 34, 22); LocalTime t2 = LocalTime.of(12, 34, 22); System.out.println(t1.equals(t2)); } }
20. It’s true! package java.time; U` UUa public final class LocalTime { U` UUa @Override public boolean equals(Object obj) { if (this Uc obj) { return true; } if (obj instanceof LocalTime) { LocalTime other = (LocalTime) obj; return hour Uc other.hour Ud minute Uc other.minute Ud second Uc other.second Ud nano Uc other.nano; } return false; } }
21. Value Object An object that represents a descriptive aspect of the domain with no conceptual identity is called a Value Object. Value Object are instantiated to represent elements of the design that we care about only for what they are, not who or which they are.
22. Data Class in Kotlin
23. Representing Data in Kotlin data class LocalTime(val hour: Byte, val minute: Byte, val second: Byte)
24. Representing Data in Kotlin data class LocalTime(val hour: Byte, val minute: Byte, val second: Byte) val t1 = LocalTime(12, 34, 22) val t2 = LocalTime(12, 34, 22) println(t1 Uc t2) U` prints true
25. Representing Data in Clojure
26. Representing Data in Clojure
27. Data More than name-value pairs!
28. A Login API Response
29. A Login API Response Login Success
30. A Login API Response Login Success First-time Login
31. A Login API Response Login Success First-time Login Bad Credentials
32. A Login API Response Login Success First-time Login Bad Credentials Login Failure
33. Representing Login Response
34. Handling Login Response
35. Representing Login Response
36. Representing Login Response
37. Representing Login Response
38. Representing Login Response
39. Representing Login Response
40. Handling Login Response
41. Handling Login Response
42. Decouple handler logic from object
43. Visitor Pattern In object-oriented programming and software engineering, the visitor design pattern is a way of separating an algorithm from an object structure on which it operates. A practical result of this separation is the ability to add new operations to existing object structures without modifying the structures. It is one way to follow the open/closed principle. - Wikipedia
44. Handling Login Response - Visitor
45. Handling Login Response - Visitor
46. Handling Login Response - Visitor
48. Decouple handler logic from object.
49. Handling Login Response
50. Handling Login Response
51. Representing Login Response sealed class LoginResponse { data class LoginSuccess(val jwtToken: String)7 LoginResponse() data class FirsTimeLogin(val sessionId: UUID)7 LoginResponse() data class BadCredentials(val message: String)7 LoginResponse() data class ServerError(val error: String)7 LoginResponse() }
52. Handling Login Response fun handleLogin(res : LoginResponse) { when(res) { is LoginResponse.LoginSuccess Uj println("Redirect to dashboard with token ${res.jwtToken}") is LoginResponse.FirsTimeLogin Uj println("Redirect to changekpassword with session id ${res.sessionId}") is LoginResponse.BadCredentials Uj println("Show bad credentials error ${res.message}") is LoginResponse.ServerError Uj { println("Log error: ${res.error}") println("Show something went wrong") } } }
53. Pattern Matching - Sub Types fun handleLogin(res : LoginResponse) { when(res) { is LoginResponse.LoginSuccess Uj println("Redirect to dashboard with token ${res.jwtToken}") is LoginResponse.FirsTimeLogin Uj println("Redirect to changekpassword with session id ${res.sessionId}") is LoginResponse.BadCredentials Uj println("Show bad credentials error ${res.message}") is LoginResponse.ServerError Uj { println("Log error: ${res.error}") println("Show something went wrong") } } }
54. fun handleLogin(res : LoginResponse) { when(res) { is LoginResponse.LoginSuccess Uj println("Redirect to dashboard with token ${res.jwtToken}") is LoginResponse.FirsTimeLogin Uj println("Redirect to changekpassword with session id ${res.sessionId}") is LoginResponse.BadCredentials Uj println("Show bad credentials error ${res.message}") is LoginResponse.ServerError Uj { println("Log error: ${res.error}") println("Show something went wrong") } } } sealed class LoginResponse { data class LoginSuccess(val jwtToken: String)7 LoginResponse() data class FirsTimeLogin(val sessionId: UUID)7 LoginResponse() data class BadCredentials(val message: String)7 LoginResponse() data class ServerError(val error: String)7 LoginResponse() } V/S
55. Pattern Matching - Value
56. Pattern Matching - Guards
57. Pattern Matching - Vector (x = 10, y = 10) (x = 10, y = 20, z = 30)
58. Pattern Matching - Vector (x = 10, y = 10) (x = 10, y = 20, z = 30)
59. 1 2 3 Pattern Matching - First & Rest
60. 1 2 3 Pattern Matching - First & Rest
61. Pattern Matching - Map Rectangle with height 12 & width 12 Circle with radius 12
62. Pattern Matching - Map Rectangle with height 12 & width 12 Circle with radius 12
64. Pattern Matching - Map & Guards
65. Pattern Matching - Map & Guards
66. Pattern Matching - Map & Guards
67. Pattern Matching - Map & Guards
68. Pattern Matching - Map & Guards
69. Pattern Matching - Map & Guards
70. Let’s do some destructuring
72. {:hour 12 :minute 34 :second 22}
73. {:hour 12 :minute 34 :second 22}
74. {:hour 12 :minute 34 :second 22} Associative Destructuring
75. {:hour "12"} Associative Destructuring Hour: 12, Minute: 00, Second: 00
76. {:hour "12"} Associative Destructuring Hour: 12, Minute: 00, Second: 00
77. fun printTimestamp(text : String) { val pattern = "(\\d\\d)7(\\d\\d)7(\\d\\d)" val regex = pattern.toRegex() val timestamp = regex.find(text)UUVgroupValues val hour = timestamp[1] val minute = timestamp[2] val second = timestamp[3] println("Hour: $hour, Minute: $minute, Second: $second") }
79. Positional Destructuring
80. Positional Destructuring
81. Software = Data + Behaviour