THE POWER OF TYPES DANNY PREUSSLER @PreusslerBerlin Copenhagen - PowerPoint PPT Presentation

THE POWER OF TYPES DANNY PREUSSLER @PreusslerBerlin Copenhagen Denmark

Do you enjoy debugging?

In an ideal world, in the right language, buggy code is impossible. The compiler simply refuses to build

In an ideal world, in the right language, buggy code is impossible. The compiler simply refuses to build

In an ideal world, in the right language, buggy code is impossible. The compiler simply refuses to build

In an ideal world, in the right language, buggy code is impossible. The compiler simply refuses to build

No language can prevent us from writing bugs!

But we can avoid as many as possible, as early as possible

TYPES

Well-typed expressions do not go wrong A theory of type polymorphism in programming. Journal of Computer and System Sciences, Robert Milner, 1978

WHAT IS A TYPE?

abstraction mechanisms over data Several Types of Types in Programming Languages Simone Martini, Universit`a di Bologna

A type is a concise, formal description of the behavior of a program fragment Type systems for programming languages, Didier Rémy, INRIA Paris

THE HISTORY OF TYPES

1950 1960 1970 1980 1990 2000 2010 2020

1950 1960 1970 1980 1990 2000 2010 2020 Types are pretty much absent

1950 1960 1970 1980 1990 2000 2010 2020 Fortran

1950 1960 1970 1980 1990 2000 2010 2020 Fortran “Two types of constants are permissible: fixed points (restricted to integers) and floating points” But at same time, “ mode ” is used instead FORTRAN manual, 1956

1950 1960 1970 1980 1990 2000 2010 2020 Fortran Algol 60 Types were born

1950 1960 1970 1980 1990 2000 2010 2020 Fortran Algol 60 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 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 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 Algol W 1966 Algol W

1950 1960 1970 1980 1990 2000 2010 2020 Fortran Algol 60 Algol W One missing piece

1950 1960 1970 1980 1990 2000 2010 2020 Fortran Algol 60 Algol W 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 Pascal

1950 1960 1970 1980 1990 2000 2010 2020 Fortran Algol 60 Algol W Pascal 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 C++ The dawn of Object Orientation

1950 1960 1970 1980 1990 2000 2010 2020 Fortran Algol 60 Algol W Pascal C++ 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++ Java The age of the internet languages

1950 1960 1970 1980 1990 2000 2010 2020 Fortran Algol 60 Algol W Pascal C++ Java 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 JS Ruby Dynamic Typed languages

1950 1960 1970 1980 1990 2000 2010 2020 Fortran Algol 60 Algol W Pascal C++ Java JS Ruby 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 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 Java Generics 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 Scala Functional Programming arises from the grave

1950 1960 1970 1980 1990 2000 2010 2020 Fortran Algol 60 Algol W Pascal C++ Java JS Ruby Java Generics Scala 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 Java Generics Scala Typescript you can write large programs in JavaScript. You just can’t maintain them. Anders Hejlsberg, 2012

1950 1960 1970 1980 1990 2000 2010 2020 Fortran Algol 60 Algol W Pascal C++ Java JS Ruby Java Generics Scala Typescript 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 Fortran 1960 Algol 60 Algol W type reconstruction 1970 Pascal starts spreading 1980 C++ 1990 Java 2000 JS Ruby Java Generics 2010 Scala Typescript Kotlin 2020

KOTLIN AND TYPES

The type system is Kotlin’s super power Nullability, 1st class functions, Nothing

If Kotlin uses the power of Types So can you!

PRIMITIVE OBSESSION

Usage of primitives instead of small objects for simple tasks

Usage of constants for coding information

Don’t put in name what can be in type

Encoding the type [..] into the name [..] is brain damaged the compiler knows the types Linus Torvalds about Hungarian notation

actually...

actually...

Don’t put in name what could be in type!

Express your Domain knowledge

Sample: At Soundcloud a URN uniquely identifies an entity: a user, track playlist… soundcloud:tracks:1234

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++

“type” properties/functions are a smell

Depending properties might be hint for hidden type

Factory methods are hint for different types

Booleans are a smell: 2 things in 1 place

Don’t let the creep in

COSTS

ALLOCATION COSTS

On JVM, objects allocated in Eden space

To avoid thread synchronization Eden is split into Thread Local Allocation Buffer

Allocating space in TLAB is often just a pointer bump

The compiler might even inline the whole class: Allocation elimination with escape analysis Urban performance legends, revisited, Brian Goetz 2005

Allocations on JVM are very cheap

A word on Android ART is optimized for allocations

Allocations are OK Types are OK Yes, even enums Modern Android development: Android Jetpack, Kotlin, and more (Google I/O 2018)

MEMORY COSTS

Memory A plain Object takes 8 bytes On Sun's JDK 1.3.1 for Windows

Memory Any wrapper will be 8 bytes larger than wrapped primitive On Sun's JDK 1.3.1 for Windows

But careful

Memory An empty String takes 40 bytes On Sun's JDK 1.3.1 for Windows