Types are becoming more important in software as programs grow larger and more complex, leading to more bugs. New types like Optional help prevent null pointer exceptions while async/await make asynchronous code more intuitive. More advanced types still being adopted include algebraic data types that model relationships between data, dependent types that allow types to depend on values, and linear types that prevent multiple uses of resources. These new types allow for stronger guarantees and more bugs caught at compile time rather than runtime.

1. TypesAreEatingTheWorld!

2. AboutMyself
MynameisDaisukeShimamoto
Pronounced"Dice-K"
Twitter/Facebook/LinkedIn:@diskshima
Current:
EngineerManageratPROGRIT(aEnglish
coachingcompany)
PastExperience:
USInvestmentBank:Java&Spring,C#&.Net
Variousstart-ups:RubyonRails,React.js,React
Native,etc.

3. Me&Types
FascinatedbyTypesinprogramming.
Justfindtheminteresting.
IwriteHaskellasahobby.
Notusingittodaysopleasedon'trunaway

4. BeforeWeStart
WillbemainlyusingTypeScriptandSwiftinthistalk.
GoodsupportforTypes.
Notcovering/using
TypeTheory
Monads
Weirdgreeksymbols(ɑ,𝛽,𝛾,𝜎,𝜋,etc.)
Soagain,pleasedon'trunaway

5. KeyTakeaway:Typesarebecomingmoreimportant!

6. WhySo?
Softwareisbecoming:
Moreandmoreadvanced
Largerandlarger
Moreandmorecomplex

7. Whichleadsto...

8. Whichleadsto... MOREBUGS!!

9. Whatcanwedo?

10. Whatcanwedo?TYPES!!

11. StartwithBasics
BasicTypes
int
-1,0,1,2,3,...
float
0.1,0.25,0.3,...
char
'a','b','c',...
string
"hello","world",...

12. AdvancedTypes
FunctionTypes
number => string :Takesinanintandreturnsastring
const f: ((n: number) => string) = function (n) {
// Do something with n.
:
return "foo";
}
Generics(Java,C#,TypeScript,etc)
function firstElement<T>(arr: T[]): T {
return arr[0];
}

13. ButTypescandomore!

14. ButTypescandomore!
Let'slookatsomefairlynew/advancedTypes!

15. Optional
Indicatesthatthevaluecouldbe null .
You'veseenoneofthese,right?
java.lang.NullPointerException
TypeError: ‘undefined’ is not an object
Optionalspreventthis.

16. Example(Swift):
let num: Optional<Int> = function_that_may_return_nil()
if let a = num { // Take the Int inside Optional<Int>.
print(a)
} else {
print("Was nil")
}

17. Optional
Thecompilercancheckthatyou'veactuallyhandledthecaseof null .
Someexamplesinotherlanguages:
Java: Optional
C#: Nullable
Kotlin: Nullable

18. FunFactabout null
null wasfirstintroducedbyTonyHoare(famousComputerScientist).
Andhelaterreferredtoitasthebillion-dollarmistake
Icallitmybillion-dollarmistake.Itwastheinventionofthenullreferencein1965(in
ALGOLW).
Wikipedia

19. Async/Await,Future,Promise
Thesearetype(orlanguage)featureforhandlingasynchronousexecutions.

20. Example(TypeScript):
function delayedPrint(msg: string, delay: number): Promise<void> {
return new Promise((resolve, reject) => {
setTimeout(() => {
console.log(msg);
resolve();
}, delay);
});
}
async function main() {
console.log("Dispatching first delayedPrint.")
delayedPrint("Hello", 1000);
console.log("Dispatching second delayedPrint.")
await delayedPrint("Hello2", 1500);
console.log("This console.log will wait for the one above.")
delayedPrint("Hello3", 1000);
}
main();

21. Output:
Dispatching first delayedPrint.
Dispatching second delayedPrint.
Hello
Hello2
This console.log will wait the one above.
Hello3

22. Async/Await,Future,Promise
Intuitive
Comparedtothecallbackhell.
SupportedbyC#,TypeScript,Kotlin,etc.
BeingaddedtootherlanguageslikeSwift,C++.
Tellshowmuchengineerslovethisfeature

23. QuickSummarySoFar
Typesareeatingtheworld
Advancesinprogramminglanguagesarespeedinguplikecrazy.
Muchslowerintheolddays(RememberPerl6?C++0x)?)
TranspilerslikeBabelhashelpedalot.

24. ButTypescandoEVENMORE!

25. ButTypescandoEVENMORE!
Let'slookatsomemoreadvancedTypesthatwemayseeinthefuture.

26. 1.AlgebraicDataTypes

27. 1.AlgebraicDataTypes
Representsrelationshipsbetweendata.
Consistsoftwokinds:
SumType
Alsocalled"enum".
ThedatacouldbeoneofA,B,C...
ProductType
ThedatacanholdanelementofAandanelementofBandsoon.
Alsocalled"struct","record".

28. ExampleofSumType(inTypeScript)
interface A {
:
}
interface B {
:
}
type A_OR_B = A | B; // Meaning it can be either A or B

29. ExampleofProductTypeinSwift:
struct ProductExample {
let a: Bool
let b: Bool
}

30. UseCases
TypeScriptExample
interface Square {
kind: "square";
size: number;
}
interface Rectangle {
kind: "rectangle";
width: number;
height: number;
}
type Shape = Square | Rectangle; // Either a Square or a Rectangle.

31. TypeScriptExample(cont'd)
function non_exhaustive(s: Shape) {
switch (s.kind) {
case "square":
return s.size * s.size;
default:
const _tmp: never = s
// ^^^^ This is a compile time error!
}
return 0;
}
function not_in_part_of_the_type(s: Shape) {
switch (s.kind) {
case "square": return s.size * s.size;
case "rectangle": return s.height * s.width;
case "circle": return s.height;
// ^^^^^^^^ This is a compile time error!
}
}

32. Obvious?Yes.
Somelanguagesdonotnotsupportthisorhavenotfullysupportedthem.
PHPProposal:PHP:rfc:adts
Kotlin:Supportsealed(exhaustive)whens
Compiletimecheckofexhaustivenessofsumtypes.

33. Why"Algebraic"?
Somethingtodowithmathbutwon'tgodeepertoday.
Irecommendreading:
Thealgebra(andcalculus!)ofalgebraicdatatypes

34. 2.DependentTypes

35. DependentTypes
AllTypessofar
MakeacleardistinctionbetweenTypesandValues
Valuesdependontheirtypes
const num: int = 1; // <-- 1 depends on int.
const str: string = "hello"; // <-- "hello" depends on string.

36. Canwenotflipthis?
i.e.haveTypesdependonValues?

37. What??

38. Let'sstartwithaproblemwewanttosolve.

39. Problem:"Functionthatexpectsevennumbers"

40. Problem:"Functionthatexpectsevennumbers"
NormalTypeScript:
function f(n: int) {
if (n % 2 != 0) {
throw "n is not even!"
} else {
// n is even.
// Do something with n.
:
}
}
f(1) // Compiler will be happy but will definitely THROW!

41. IntroducingDependentTypes
DependentTypesallowyoutousevaluesinthetypes.
// This is made-up syntax. Doesn't actually work!
function f(n: { int | n % 2 == 0 }) {
// ^^^^^^^^^^ Compile time check!
:
}
f(1) // Compiler will error!

42. DependentTypes
EncodesmorelogicintotheType.
Morecompiletimechecks!
ByauseronStackoverflow:
Dependenttypesenablelargersetoflogicerrorstobeeliminatedatcompile
time.

43. DependentTypes
Notmuchsupportyet
Onlyafewlanguagessupportit:
Agda
Idris
Let'sseeifmainstreamlanguagesadoptit

44. 3.LinearTypes

45. 3.LinearTypes
Againlet'sstartwiththeproblem.

46. Problem:"Howcanwepreventuseofvariableswhen
theyshouldnotbeused?"

47. Problem:"Howcanwepreventuseofvariableswhen
theyshouldnotbeused?"
Examples:
Useafter free .
Double free .
Accessingaclosedfilehandler.

48. IntroducingLinearTypes
LinearTypesmustbeusedonceandonlyonce.
Thekeyismustandonce.

49. UseCases#1
Linearresources
Files,networksockets,etc.
// Again made-up syntax. Does not actually work.
linearfunc readFile(filepath: string): string {
const fileHandle = open(filepath);
const content = readFile(fileHandle);
return content;
// Oops! Forgot to close `fileHandle`!
// Compiler can automatically emit, operation to close the handle.
}

50. UseCase#2
Performance
Ifyouknowitwon'tbeused,youcanoptimizeit.
// Again made-up syntax. TypeScript does not have this!
linearfunc f(str: string): string {
const str2 = str + "aaaaaa"; // Plain TypeScript will allocate a new memory for this.
return str2; // <- The compiler can make a decision and overwrite str in memory for performance!
}

51. Summary
SomerecentTypesseeninmainstreamlanguages.
Optional
Await/Async,Future,Promise
MoreAdvancedTypes
AlgebraicDataTypes
DependentTypes
LinearTypes

52. Thanks!

53. Attributions
HaskellIcon:https://icon-icons.com/icon/file-type-haskell/130552
SwiftIcon:https://icon-icons.com/icon/swift-original-logo/146332
TypeScriptIcon:https://icon-icons.com/icon/file-type-typescript-official/130107