![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];
}](https://image.slidesharecdn.com/typesareeatingtheworld-210926062452/85/Types-are-eating-the-world-12-320.jpg)
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Types are eating the world
- 9. Whatcanwedo?
- 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]; }
- 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
- 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
- 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! } }
- 34. 2.DependentTypes
- 35. DependentTypes AllTypessofar MakeacleardistinctionbetweenTypesandValues Valuesdependontheirtypes const num: int = 1; // <-- 1 depends on int. const str: string = "hello"; // <-- "hello" depends on string.
- 37. What??
- 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!
- 44. 3.LinearTypes
- 47. Problem:"Howcanwepreventuseofvariableswhen theyshouldnotbeused?" Examples: Useafter free . Double free . Accessingaclosedfilehandler.
- 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! }
- 52. Thanks!