The Power of Types, KotlinConf 2019

From Assembler, over Fortran and C to modern Kotlin, we came a long way and improved the way we can express our thoughts in code.

One thing that happened during this journey is that languages allow us to use types for our problem domain, independent of the underlying computer architecture. Types became a powerful tool.

Types improve readability which probably is the most important aspect of programming! But types also prevent you from making mistakes at compile time. This is why Kotlin translated the null problem into the type system.

We can use these powers in our daily lives. We can write better code by avoiding “primitive obsession”. I’ll show you how!

Transcript

1. Copenhagen Denmark THE POWER OF TYPES DANNY PREUSSLER @PreusslerBerlin
3. Do you enjoy debugging?
4. In an ideal world, in the right language, buggy code is impossible. The compiler simply refuses to build
5. In an ideal world, in the right language, buggy code is impossible. The compiler simply refuses to build
6. In an ideal world, in the right language, buggy code is impossible. The compiler simply refuses to build
7. In an ideal world, in the right language, buggy code is impossible. The compiler simply refuses to build
8. No language can prevent us from writing bugs!
9. But we can avoid as many as possible, as early as possible
10. TYPES
11. Well-typed expressions do not go wrong A theory of type polymorphism in programming. Journal of Computer and System Sciences, Robert Milner, 1978
12. WHAT IS A TYPE?
13. abstraction mechanisms over data Several Types of Types in Programming Languages Simone Martini, Universit`a di Bologna
14. A type is a concise, formal description of the behavior of a program fragment Type systems for programming languages, Didier Rémy, INRIA Paris
15. THE HISTORY OF TYPES
16. 1950 1960 1970 1980 1990 2000 2010 2020
17. Types are pretty much absent 1950 1960 1970 1980 1990 2000 2010 2020
18. 1950 1960 1970 1980 1990 2000 2010 2020 Fortran
19. “Two types of constants are permissible: fixed points (restricted to integers) and floating points” FORTRAN manual, 1956 But at same time, “mode” is used instead 1950 1960 1970 1980 1990 2000 2010 2020 Fortran
20. 1950 1960 1970 1980 1990 2000 2010 2020 Fortran Algol 60 Types were born
21. Integers are of type integer. All other numbers are of type real. Algol 60 1950 1960 1970 1980 1990 2000 2010 2020 Fortran Algol 60
22. the results of any program [..] should be comprehensible without knowing anything about the machine or its storage layout. Tony Hoare 1960 1950 1960 1970 1980 1990 2000 2010 2020 Fortran Algol 60
23. I realised that [types] were essential not only for determining memory requirements, but also for avoiding machine-dependent error Tony Hoare 1960 1950 1960 1970 1980 1990 2000 2010 2020 Fortran Algol 60
24. 1950 1960 1970 1980 1990 2000 2010 2020 Fortran Algol 60 Algol W 1966 Algol W
25. One missing piece 1950 1960 1970 1980 1990 2000 2010 2020 Fortran Algol 60 Algol W
26. the type system (including user-defined types) [should] guarantee that only the prescribed operations on a type could operate on its values James H. Morris. Types are not sets, New York, NY, USA, 1973. ACM 1950 1960 1970 1980 1990 2000 2010 2020 Fortran Algol 60 Algol W
27. 1950 1960 1970 1980 1990 2000 2010 2020 Fortran Algol 60 Algol W Pascal
28. Types became a central feature of programming languages as we understand them today 1950 1960 1970 1980 1990 2000 2010 2020 Fortran Algol 60 Algol W Pascal
29. The dawn of Object Orientation 1950 1960 1970 1980 1990 2000 2010 2020 Fortran Algol 60 Algol W Pascal C++
30. Type structure is a syntactic discipline for enforcing levels of abstraction Types, abstraction and parametric polymorphism, John C. Reynolds, 1983 1950 1960 1970 1980 1990 2000 2010 2020 Fortran Algol 60 Algol W Pascal C++
31. The age of the internet languages 1950 1960 1970 1980 1990 2000 2010 2020 Fortran Algol 60 Algol W Pascal C++ Java
32. Object-oriented languages had made static typing so painful that many preferred to give up and just wing it. Ben Lynn, https://benlynn.blogspot.com/ 1950 1960 1970 1980 1990 2000 2010 2020 Fortran Algol 60 Algol W Pascal C++ Java
33. Dynamic Typed languages 1950 1960 1970 1980 1990 2000 2010 2020 Fortran Algol 60 Algol W Pascal C++ Java JS Ruby
34. It is important to note that this is different than being typeless Dynamically Typed Languages, Laurence Tratt, Bournemouth University 1950 1960 1970 1980 1990 2000 2010 2020 Fortran Algol 60 Algol W Pascal C++ Java JS Ruby
35. the chief technical difference between them being when types are enforced Dynamically Typed Languages, Laurence Tratt, Bournemouth University 1950 1960 1970 1980 1990 2000 2010 2020 Fortran Algol 60 Algol W Pascal C++ Java JS Ruby
36. After you ship, it costs you about 10,000 times as much to fix a software bug Bill Joy, Java-One, 1999 1950 1960 1970 1980 1990 2000 2010 2020 Fortran Algol 60 Algol W Pascal C++ Java JS Ruby Java Generics
37. Functional Programming arises from the grave 1950 1960 1970 1980 1990 2000 2010 2020 Fortran Algol 60 Algol W Pascal C++ Java JS Ruby Scala Java Generics
38. Functional programming languages are traditionally typed (Scheme and Erlang are exceptions) Type systems for programming languages, Didier Rémy, INRIA Paris 1950 1960 1970 1980 1990 2000 2010 2020 Fortran Algol 60 Algol W Pascal C++ Java JS Ruby Scala Java Generics
39. Anders Hejlsberg, 2012 you can write large programs in JavaScript. You just can’t maintain them. 1950 1960 1970 1980 1990 2000 2010 2020 Fortran Algol 60 Algol W Pascal C++ Java JS Ruby Scala Typescript Java Generics
40. The typed v.s. untyped flavor [..] should not be confused with [..] whether types [..] are explicit or implicit. Type systems for programming languages, Didier Rémy, INRIA Paris 1950 1960 1970 1980 1990 2000 2010 2020 Fortran Algol 60 Algol W Pascal C++ Java JS Ruby Scala Typescript Java Generics
41. type reconstruction starts spreading 1950 1960 1970 1980 1990 2000 2010 2020 Fortran Algol 60 Algol W Pascal C++ Java JS Ruby Scala Kotlin Typescript Java Generics
42. KOTLIN AND TYPES
43. The type system is Kotlin’s super power Nullability, 1st class functions, Nothing
44. If Kotlin uses the power of Types So can you!
45. PRIMITIVE OBSESSION
46. Usage of primitives instead of small objects for simple tasks
47. Usage of constants for coding information
55. Don’t put in name what can be in type
56. Encoding the type [..] into the name [..] is brain damaged the compiler knows the types Linus Torvalds about Hungarian notation
62. actually...
63. actually...
65. Don’t put in name what could be in type!
66. Express your Domain knowledge
67. Sample: At Soundcloud a URN uniquely identifies an entity: a user, track playlist… soundcloud:tracks:1234
69. Anytime you find yourself writing code of the form if the object is of type T1, then do something, but if it’s of type T2, then do something else, slap yourself. Scott Meyers, Effective C++
70. “type” properties/functions are a smell
71. Depending properties might be hint for hidden type
72. Factory methods are hint for different types
77. Booleans are a smell: 2 things in 1 place
79. Don’t let the creep in
87. COSTS
88. ALLOCATION COSTS
89. On JVM, objects allocated in Eden space
90. To avoid thread synchronization Eden is split into Thread Local Allocation Buffer
91. Allocating space in TLAB is often just a pointer bump
92. The compiler might even inline the whole class: Allocation elimination with escape analysis Urban performance legends, revisited, Brian Goetz 2005
93. Allocations on JVM are very cheap
94. A word on Android ART is optimized for allocations
95. Allocations are OK Types are OK Yes, even enums Modern Android development: Android Jetpack, Kotlin, and more (Google I/O 2018)
96. MEMORY COSTS
97. Memory A plain Object takes 8 bytes On Sun's JDK 1.3.1 for Windows
98. Memory Any wrapper will be 8 bytes larger than wrapped primitive On Sun's JDK 1.3.1 for Windows
99. But careful
100. Memory An empty String takes 40 bytes On Sun's JDK 1.3.1 for Windows
101. Memory Boolean: header has 12 bytes + 1 for the boolean + 3 for the granularity On HotSpot JVM 1.7.0_51
102. Memory its "size" isn't something that's precisely defined https://docs.oracle.com/javase/tutorial/java/nutsandbolts/datatypes.html
103. Kotlin compiler translates to int
104. Kotlin compiler translates to java.lang.Integer
105. Kotlin compiler can use primitive int inside Age
106. Kotlin compiler translates to int
107. Kotlin keeps Age with int
108. GARBAGE COSTS
109. the performance of the garbage collector is not determined by the number of dead objects but rather by the number of live ones Analyzing Java Memory, Java enterprise performance book
110. Short lived objects are cheap
111. SUM UP
112. • Types improve readability (documentation) • Types help compile time correctness (safety, machine checked documentation) • Types improve abstraction (modularity) -> Types are enabler Sum up
113. Watch out for “hidden type” smells: • Types information in names • Type attributes • Booleans • Primitives Sum up
114. My goal was to ensure that all use of references should be absolutely safe, with checking performed automatically by the compiler Tony Hoare about Algol W
115. But I couldn't resist the temptation to put in a null reference, simply because it was so easy to implement. Tony Hoare about Algol W
116. call it my billion-dollar mistake Tony Hoare about Algol W
117. Readability Let the compiler do the work!
118. TYPE ALL THE THINGS!
119. • Several Types of Types in Programming Languages Simone Martini, Universit`a di Bologna https://arxiv.org/pdf/1510.03726 • History and Philosophy of Computing Third International Conference, HaPoC 2015, Pisa, Italy • Type systems for programming languages Didier Rémy, INRIA Paris, http://gallium.inria.fr/~remy/mpri/cours1.pdf • A theory of type polymorphism in programming. Journal of Computer and System Sciences, Robert Milner, 1978 https://homepages.inf.ed.ac.uk/wadler/papers/papers-we-love/milner-type-polymorphism.pdf • Dynamically Typed Languages Laurence Tratt,Bournemouth University, 2009 https://tratt.net/laurie/research/pubs/html/tratt__dynamically_typed_languages/ Sources History of types
120. • Type Wars, The Clean Code Blog, Uncle Bob http://blog.cleancoder.com/uncle-bob/2016/05/01/TypeWars.html • From Primitive Obsession to Domain Modelling, Mark Seemann https://blog.ploeh.dk/2015/01/19/from-primitive-obsession-to-domain-modelling/ • Phantom types in Kotlin, Danny Preussler https://proandroiddev.com/phantom-types-in-kotlin-afd3f59fde10? • Primitive Data types, Oracle https://docs.oracle.com/javase/tutorial/java/nutsandbolts/datatypes.html Sources Types
121. • The cost of object creation in Java, including garbage collection https://www.bettercodebytes.com/the-cost-of-object-creation-in-java-including-garbage-collection/ • Thread-Local Allocation Buffers in JVM https://alidg.me/blog/2019/6/21/tlab-jvm • Urban performance legends, revisited https://www.ibm.com/developerworks/java/library/j-jtp09275/index.html#artrelatedtopics • E-book: Java enterprise performance https://www.dynatrace.com/resources/ebooks/javabook/ • Do you know your data size? https://www.javaworld.com/article/2077496/java-tip-130--do-you-know-your-data-size-.html • The impact of Garbage Collection on Application Performance https://www.dynatrace.com/resources/ebooks/javabook/impact-of-garbage-collection-on-performance/ Sources Costs
122. #KotlinConf THANK YOU AND REMEMBER TO VOTE Danny Preussler @ PreusslerBerlin