コードには型アノテーションよりも要件アノテーションを増やせ！/harajukuts2

2022/1/28 Harajuku.ts Meetup #2 にて使用した資料です。

11ページ目はString#join()ではなくArray#join()の誤りでした。お詫びいたします。

Transcript

1. +BO
   
   
   
   )BSBKVLVUT
   .FFUVQ
   
   !PLVOPLFOUBSP ίʔ υʹ͸ܕΞϊςʔγϣϯΑ Γ ΋ 
 ཁ݅ΞϊςʔγϣϯΛ૿΍ͤ ʂ
2. ୭ w Ԟ໺
   ݡଠ࿠
   !PLVOPLFOUBSP
   w ΫϨε΢ΣΞגࣜձࣾ
   w 5ZQF4DSJQUྺ
   ೥
   w ϑϩϯ τΤϯ υ ɾ όοΫΤϯ υ
3. 5ZQF4DSJQUొஃͷྺ࢙
4. 5ZQF4DSJQUొஃͷྺ࢙ ࠓ೔͸͜Εͷଓ͖Ͱ͢ˢ
5. ͳͥ5ZQF4DSJQUΛ࢖͏ͷ͔ ʁ w +BWB4DSJQU͸ॻ͍͍ͯͯϛεΛ͢Δݴޠ͔ͩΒͰ͋Δ
   w ΋ͪΖΜ5ZQF4DSJQU΋ॻ͍͍ͯͯϛεΛ͢ΔݴޠͰ͋Δ
   w ϛε͔ͯ͠Βϛεʹؾ෇͘ ·Ͱͷ͕࣌ؒ୹͚Ε͹୹͍΄Ͳخ͍͠
   w ͦ΋ͦ΋ϛε͠ͳ͍Α ͏ͳߏจͰ͋Ε͹΋ͬͱخ͍͠
   wʮઈରʹϛεΛ͠ͳ͍ਓʯ ͕։ൃ͢ΔͳΒ+BWB4DSJQUͷ··͓޷͖ʹͲ͏ ͧ
6. ਓ͸ϛεΛ͢ΔΜͰ͢ ʂ
7. ۃ୺ͳྫ ͜Ε͸+BWB4DSJQUͷίʔ υ 
 ͭͷ਺஋Λ଍ͯ͠߹ܭΛฦ͢
   add()
   ؔ਺ function add(a, b) { return a + b; }
8. ۃ୺ͳྫ Ͱ΋ add("Hello", "World") ͳΜͯ͜ͱ΋Ͱ͖Δ 
 ʢ݁Ռ͸
   )FMMP8PSMEʣ function add(a, b) { return a + b; }
9. ۃ୺ͳྫ function add(a, b) { return a + b; } ࣮૷ऀ͸਺஋ͷ଍͠ࢉΛ૝ఆ࣮ͯ͠૷ͨ͠ͷʹɺ 
 ར༻ऀ͸͜ͷؔ਺Λจࣈྻͷ࿈݁ͷͨΊͩͱޡղͯ͠͠·ͬͨ ʂ
10. ҙࢥૄ௨ͷϛε w ίʔ υΛॻ͍͍ͯΔ্Ͱͷϛε͸UZQPɺ ͏ ͔ͬΓ࡟আͳͲ༷ʑ
    w ։ൃऀಉ࢜ͷҙࢥૄ௨͕ίʔ υ্Ͱ׬݁͠ͳ͍͜ͱ΋ 
 ҙࢥૄ௨ͷϛεͱݺ΂Α ͏
    w จࣈྻ࿈݁ؔ਺ͱޡղͯ͠͠·ͬͨ։ൃऀ͸ɺ 
 add()
    ؔ਺͕Ͳ͏͍͏ؔ਺ͳͷ͔࣮૷ऀຊਓʹฉ͘ ·Ͱ೺ѲͰ͖ͳ͔ͬͨ
11. ଞਓͷίʔ υɺ ਖ਼͠ ͘ղऍͯ͠ಡΜͰ·͔͢ ʁ w ΋ͪΖΜ͜Ε͸͘͢͝ۃ୺ͳྫ 
 ʢ
    + ͸਺஋ͷՃࢉʹͷΈ༻͍ͯɺ จࣈྻ࿈݁͸ String#join() ΍5FNQMBUF
    MJUFSBMTΛ࢖͏ํ͕Α Γ਌੾ʣ
    w ͔͠͠ɺ ۀ຿͸͜͏͍ͬͨ ʮଞਓͷίʔ υΛᴥᴪͳ͘ղऍͰ͖͍ͯΔ͔ʯ ͱ͍͏ 
 ධՁͷ࿈ଓͰ͋Δ
    w ίʔ υதͷ৘ใྔ͕๡͍͠ͱɺ ͨͱ͑1BSTBCMFͳίʔ υͰ͋ͬͨͱͯ͠΋ 
 ଞͷ։ൃऀͷҙਤ·Ͱղऍ͢Δͷ͸೉͍͠
12. ܕΞϊςʔγϣϯ function add(a: number, b: number): number { return a + b; } 5ZQF4DSJQUͰ͸ɺ Ҿ਺΍໭Γ஋ͷܕΛදه͢Δ 
 ͜ΕΛܕΞϊςʔγϣϯ
    5ZQF
    BOOPUBUJPOT
    ͱ͍͏
13. ܕΞϊςʔγϣϯ function add(a: number, b: number): number { return a + b; } ܕΞϊςʔγϣϯͷ͓͔͛Ͱɺ 5ZQF4DSJQUίϯύΠ ϥ͚ͩͰͳ͘ 
 ίʔ υΛಡΉਓؒʹ΋ҙਤΛղऍ͢Δखॿ͚ͱͳΔ
    ʮ͋ɺ ͜Ε͸
    number
    ͔ͩΒจࣈྻ࿈݁ʹ࢖͏ؔ਺͡Όͳ͍ͳ ʂ ʯ
14. ʜͱ͍͏࿩͸೥લޙʹࢄʑ͞Ε· ͨ͠
15. ೥͸ܕΞϊςʔγϣϯॻ͍ͯ·͢ΑͶ w ͕͢͞ʹ5ZQF4DSJQU΋όʔδϣϯYʹಥೖ͠੒ख़͖ͯͨ͠
    w पΓͰॻ͍͍ͯΔ։ൃऀ΋͔ͳΓ૿͑ͨ
    w --noImplicitAny --noImplicitReturns ͳͲͷ 
 UTDPO fi H
    $PNQJMFS
    0QUJPOTͷ͓͔͛Ͱ 
 Ξϊςʔγϣϯͷॻ͖࿙ΕΛ๷͙ํ๏΋௕೥ཱ֬͞Ε͍ͯΔ
16. ܕΞϊςʔγϣϯ͸Έͳ͞Μॻ͍͍ͯΔͱࢥ͍·͢ͷͰɺ 
 ͜Ε͔Β͸ ʮཁ݅Ξϊςʔγϣϯʯ Λॻ͍ͯΈ·ͤΜ͔
17. ཁ݅Ξϊςʔγϣϯ ʁ w ຊߘͷ଄ޠ
    w ͪΐͬͱΩϟονʔͳλΠ τϧʹ͔͚ͨͬͨͩ͠ͳͷͰ 
 άάͬͯ΋ެࣜͷ υΩϡϝϯ τͱ͔͸ग़͖ͯ·ͤΜ
    w ܕΞϊςʔγϣϯʹܕҎ্ͷ৘ใྔΛ΋ͨͤΔ͜ͱͰ 
 ೝࣝͷᴥᴪΛΑ Γແ͘ ͢͜ͱΛ໨తͱ͢Δͷ͕ຊ࣭
18. ͜ ͏͍͏ ͜ͱɺ ͨ͜͠ͱ͋Δਓ type UserId = string; type BookId = string; ຊΛ؅ཧ͢ΔΞϓϦ 
 UserId
    ΋
    BookId
    ΋จࣈྻͳΜ͚ͩͲ۠ผ͍ͨ͠ʜ
19. type UserId = string; type BookId = string; async function fetchBook(id: BookId): Promise<Book> { // } export function BookCard(): JSX.Element { const [book, setBook] = useState<Book | null>(null); useEffect(() => { (async (): Promise<void> => { const result = await fetchBook(); setBook(result); })(); }, []); return <></>; } ͜Μͳঢ়گ͕͋ͬͨͱ͠·͠ΐ ͏
20. type UserId = string; type BookId = string; async function fetchBook(id: BookId): Promise<Book> { // } export function BookCard(): JSX.Element { const [book, setBook] = useState<Book | null>(null); useEffect(() => { (async (): Promise<void> => { const result = await fetchBook(); setBook(result); })(); }, []); return <></>; } fetchBook()
    ؔ਺ʹ͸
    BookId
    ܕͷҾ਺Λ౉ͤ͹Αͦ͞͏ Ͱ͢
21. const id: BookId = 'ckyx69gli000009ju65mvhyw7'; const result = await fetchBook(id); Αͦ͞͏
22. const id: UserId = 'ckyx6c8xc000009jm8acefv2v'; const result = await fetchBook(id); ຊ౰ʹ ʁ ʁ ʁ 
 ίϯύΠϧ௨ͬͯΔΑ ʁ ʁ ʁ
23. const result = await fetchBook('͜Μʹͪ͸'); ͳΜͳΒ͜Ε΋௨Δ
24. ίϯύΠ ϥ͸۠ผ͠·ͤΜ w type
    Λ࢖ͬͯ
    string
    ʹผ໊Λ͚ͭͯ΋ 
 ͦΕ͸͋͘ ·Ͱ΋ΤΠ ϦΞε ʢผ໊ʣ ʹ͗͢ͳ͍
    w ͳͷͰυΩϡϝϯ τʹ΋ͪΌΜͱ5ZQF
    "MJBTFTͱॻ͔Ε͍ͯΔ 
 https://www.typescriptlang.org/docs/handbook/advanced-types.html#type-aliases
    w ਓؒʹ͸ผ໊Ͱ͋Δ͜ͱ͸ࣝผͰ͖Δ͕ 
 ίϯύΠ ϥʹ͸
    string
    ʹผ໊Λ෇͚ͨ͜ͱ͔͠఻Θ͍ͬͯͳ͍
    w UserId
    ͱ
    BookId
    ͕ޓ͍ʹ
    string
    ͷผ໊Ͱ͋Δͱ͍͏͚ͩͰ 
 ͦΕΒ͕ޓ͍ʹ۠ผ͞Ε͏ Δ΂͖ͱ͍͏ཁ݅·Ͱ͸ίϯύΠ ϥʹ఻Θ͍ͬͯͳ͍
25. ͳΒ͹Ϋϥε͔ ʁ class UserId { constructor(public readonly value: string) {} } class BookId { constructor(public readonly value: string) {} } UserId
    ͱ
    BookId
    ΛͦΕͧΕ
    class
    Ͱએݴͯ͠Έͨ
26. const id = new BookId('ckyx69gli000009ju65mvhyw7'); const result = await fetchBook(id); ͕͢͞ʹࠓ౓͸Αͦ͞͏ ʁ
27. const id = new UserId('ckyx6c8xc000009jm8acefv2v'); const result = await fetchBook(id); ͩΊͰ͢ 
 ͜Ε΋ίϯύΠϧ͕௨Δ
28. 5ZQF4DSJQU͸4USVDUVSBM
    5ZQJOHͰ͋Δ w 5ZQF4DSJQU͸ܕͷผ໊Ͱ۠ผͨ͠Γɺ Ϋϥε໊͕ҟͳΔ͜ͱͰ۠ผ͢ΔͷͰ͸ͳ͘ 
 ৗʹ ʮϓϩύςΟͷߏ੒ʯ ʹΑͬͯܕͷ۠ผΛ͚ͭΔ
    w ͜͏͍ͬͨܕͷ൑ผํࣜΛ4USVDUVSBM
    5ZQJOHͱ͍͏
    w ͜Ε͸υΩϡϝϯ τʹ΋هࡌ͞Ε͍ͯΔ 
 https://www.typescriptlang.org/docs/handbook/type-compatibility.html
    w ܕ໊ͷҧ͍͚ͩͰܕ͕ҟͳ͍ͬͯΔͱ൑ผ͢Δํࣜ͸/PNJOBM
    5ZQJOHͱ͍͏
    w 5ZQF4DSJQU͸ͪ͜Βͷํࣜ͸࠾༻͍ͯ͠ͳ͍
29. ϓϩύςΟͷҰக class UserId { constructor(public readonly value: string) {} } class BookId { constructor(public readonly value: string) {} } value
    ͱ͍͏ ϓϩύςΟ͕ݸ͋ΔΫϥε 
 ͱ͍͏఺Ͱɺ ߏ଄͕Ұக͍ͯ͠Δ 
 Αͬͯ4USVDUVSBM
    5ZQJOHʹج͍ͮͯ͜ΕΒ͸ಉҰܕͱΈͳ͞ΕΔ
30. ϓϩύςΟ ΛҰகͤ͞ͳ͍Α ͏ʹ͢Δ class UserId { userId: unknown; constructor(public readonly value: string) {} } class BookId { bookId: unknown; constructor(public readonly value: string) {} } ͦΕͧΕͷΫϥεʹҟͳΔ໊લͷμϛʔϓϩύςΟ Λ଍͢͜ͱͰ 
 ߏ଄͕Ұக͠ͳ͍Α ͏ʹͨ͠
31. const id = new UserId('ckyx6c8xc000009jm8acefv2v'); const result = await fetchBook(id); Argument of type 'UserId' is not assignable to parameter of type 'BookId'. Property 'bookId' is missing in type 'UserId' but required in type 'BookId'.(2345) Τϥʔʹͳͬͯ ͘Εͨ
32. ʜͱ͍͏࿩͸೥ʹ͠· ͨ͠
33. ʜͱ͍͏࿩͸೥ʹ͠· ͨ͠ 
    5ZQF4DSJQUಋೖͰಘΒΕΔ ʮม͍͑ͯ͘༐ؾʯ 
 https://speakerdeck.com/okunokentaro/the-courage-to-change-by-typescript
34. Ϋϥε๏͸Կ͕Πέͯͳ͍͔ w 5ZQF4DSJQUͰΫϥεશൠΛ࢖͏ ͜ͱͷੋඇΛड़΂ΔΘ͚Ͱ͸ͳ͍
    w /PNJOBM
    5ZQJOH ʮͬΆ͍ʯ ͜ͱΛ͢ΔͨΊʹΫϥεΛಋೖ͢Δͷ͸Πέͯͳ͍
    w ͳ͔ͥ ʁ
35. const id = new UserId('ckyx6c8xc000009jm8acefv2v'); await fetch(`https://something/api/users/${id}`); 5FNQMBUF
    MJUFSBMTʹͯ ͜ͷΑ ͏ʹύεʹ*%ؚ͕·ΕΔΑ ͏ͳ63-͸Α ͘ ͋Δ 
 ݁Ռ͸ ʁ
36. https://something/api/users/[object Object] 👆 👆 👆 👆 👇 👇👇 👇 👇
37. Ϧςϥϧͱ ͯ͠ѻ͑ͳ͍ w new UserId()
    ͍ͯ͠ΔͨΊɺ ݁Ռ͸
    typeof id === 'object'
    ͱͳΔ
    w จࣈྻϦςϥϧͰ͸ͳ͘ɺ
    value
    ΛϓϩύςΟ ͱ ͯ࣋ͭ͠ΦϒδΣΫ τʹͳΔ
    w toString()
    Λ࣮૷͢Ε͹
    [object Object]
    ͸ճආͰ͖Δ͕ 
 ͜ͷख๏Λࢼ͢ࡍʹຖճͦͷ࣮૷͕ඞཁ
    w μϛʔϓϩύςΟ Λੜ΍͞ͳ͖ΌࣝผͰ͖ͳ͍ͷ΋ඇຊ࣭త
    w Ϧςϥϧͷ··ѻ͑ͯɺ ͔ͭ/PNJOBM
    5ZQJOHͬΆ͍ܕ൑ผΛ͢Δʹ͸ʜ ʁ
38. ྩ࿨࠷৽൛
39. UZQF
    /PNJOBM w type Nominal<T, U>
    Λએݴ͢Δ
    w { __brand: U }
    ͱ͍͏ΦϒδΣΫ τͱͷަࠩܕ
    &
    ʹ͢Δ͜ͱͰϦςϥϧͷ·· ۠ผͰ͖ΔΑ ͏ʹ͢Δ
    w ਖ਼֬ͳग़య͸ൃݟͰ͖͍ͯͳ͍͕ෳ਺ͷจݙ͋Γ
    w #SBOEFE
    5ZQFTͱ΋ݺ͹Ε͍ͯΔ͕ 
 ʮ/PNJOBM
    5ZQJOHΛ࣮ݱ͍ͨ͠ͷ͔ͩΒʯ ͱ͍͏҆௚ͳ೔ຊਓతޠ๏Ͱ 
 ࠓճ͸
    Nominal<T, U>
    ͱͨ͠ export type Nominal<T, U extends string> = T & { __brand: U };
40. /PNJOBMܕΛ࢖ͬͯ࠶௅ઓ type Nominal<T, U extends string> = T & { __brand: U }; type BookId = Nominal<string, 'BookId'>; type UserId = Nominal<string, 'UserId'>; const id = 'ckyx6c8xc000009jm8acefv2v' as UserId; const result = await fetchBook(id); Argument of type 'UserId' is not assignable to parameter of type 'BookId'. Type 'UserId' is not assignable to type '{ __brand: "BookId"; }'. Types of property '__brand' are incompatible. Type '"UserId"' is not assignable to type '"BookId"'.(2345) ͪΌΜͱ۠ผͰ͖͍ͯΔ
41. type Nominal<T, U extends string> = T & { __brand: U }; type BookId = Nominal<string, 'BookId'>; type UserId = Nominal<string, 'UserId'>; const id = 'ckyx6c8xc000009jm8acefv2v' as UserId; const result = await fetchBook(id); ʮͰ΋
    BT
    ېࢭͯ͠·ͤΜͰͨ͠ ʁ ʯ
42. લճͷ͓͞Β͍ https://speakerdeck.com/okunokentaro/techstand6 Ԟ໺ݡଠ࿠͸લճͷ5ZQF4DSJQUొஃʹͯ
    BT
    Λېࢭ͍ͯͨ͠ ʂ ʂ ʂ
43. "TTFSUJPO
    GVODUJPOTΛ࢖͏ Α ͏ʹ͢Δ w ͜ͷख๏Ͱ͸ΧδϡΞϧʹ
    as
    ͕ग़͖ͯͯ͠·͍ ʮBTېࢭʯ ʹ൓ͯ͠͠· ͏
    w ͦͷͨΊɺ
    Nominal<T, U>
    ܕͷ஋Ͱ͋Δͱ͍ࣔͨ͠৔߹͸ඞͣ 
 5ZQF
    QSFEJDBUFTɺ ·ͨ͸"TTFSUJPO
    GVODUJPOTΛ࢖͏ Α ͏ʹ͢Δ
44. BTTFSU4USJOH
    ؔ਺Λ࡞ͬͯΈΔ export function isString(v: unknown): v is string { return typeof v === 'string'; } export function assertString(v: unknown, target = ''): asserts v is string { if (!isString(v)) { throw new Error(`${target} should be string`.trim()); } } ౰ͨΓલͷΑ ͏ͳ಺༰ͷؔ਺͕ͩɺ 
 unknown
    ܕΛ
    string
    ܕͱΈͳͨ͢Ίʹ͸ɺ Θ͟Θ͟͜͏͍ͬͨؔ਺͕ඞཁ
45. /PNJOBMܕͱ"TTFSUJPO
    GVODUJPOTͷԠ༻ import { isString } from './assert-string'; import { Nominal } from './nominal'; type FilledString = Nominal<string, 'FilledString'>; function isFilledString(v: unknown): v is string { return isString(v) && v !== ''; } function assertFilledString( v: unknown, target = '' ): asserts v is FilledString { if (!isFilledString(v)) { throw new Error(`${target} should be not empty string`.trim()); } } type FilledString
    Λએݴ͠ɺ ඞۭͣจࣈྻͰ͸ͳ͍͜ͱΛද໌͢Δ
46. /PNJOBMܕͷෳ߹ import { FilledString, assertFilledString } from '../utils/filled-string'; import { Nominal } from '../utils/nominal'; export type UserId = Nominal<FilledString, 'UserId'>; function assertUserId(v: unknown): asserts v is UserId { assertFilledString(v); } export function asUserId(v: unknown): UserId { assertUserId(v); return v; } ͞Βʹɺ
    FilledString
    ܕΛຬͨ͢൑ผՄೳܕͱͯ͠
    type UserId
    Λએݴ͢Δɻ 
 ಉख๏Ͱએݴ͢Δ
    type BookId
    ͱίϯύΠ ϥ͕۠ผͰ͖Δ্ʹ 
 ۭจࣈؚ͕·Εಘͳ͍͜ͱ΋อূࡁΈ ʂ 
 ʢ"TTFSUJPO
    GVODUJPOʹ͸ࣗಈςε τͷ࣮ࢪ͕ඞਢʣ
47. Ԡ༻ͷՄೳੑ͸ແݶେ w ͜ͷख๏Λ׆༻͢Δͱ Ϧςϥϧͷදݱͷ෯͕޿͕Δ
    w ྫ͑͹ʜ
    w ۭจࣈྻΛېࢭ͢Δ6TFS*Eܕ
    w ಛఆͷਖ਼نදݱΛຬ͍ͨͯ͠ͳ͍ͱΤϥʔͱͳΔ'PSNFEܕ
    w খ਺஋΍/B/ΛೝΊͳ͍6OJY5JNFܕ
    w ۠ผՄೳͳ4FDPOEܕͱ.JMMJTFDPOEܕ
    w ͳͲͳͲ
48. ܕΞϊςʔγϣϯ͸ ʮܕ͔͠Θ͔Βͳ͍ʯ w fetchBook(id: string)
    Ͱ͸ 
 ͳΜΒ͔ͷจࣈྻΛҾ਺ʹͱΔ͜ͱ ͔͠Θ͔Βͳ͍
    w ͦΕ͸
    UserId
    ͔΋͠Εͳ͍͠ɺ ۭจࣈྻΛ౉ͯ͠΋͍͍͔΋͠Εͳ͍
    w ܕΞϊςʔγϣϯ͔Β͸ ʮ
    string
    ܕͷ஋Ͱ͋Δ͜ͱʯ Ҏ֎ͳʹ΋Θ͔Βͳ͍
    w ೥લͷ+BWB4DSJQUˠ5ZQF4DSJQUͷ࣌୅͸ɺ ͜ΕͰ΋ཱ೿ͳ΋Μͩͬͨ
49. ܕΞϊςʔγϣϯʹؚΊΔ৘ใྔΛ૿΍͢ w type BookId = Nominal<FilledString, 'BookId'>
    Λએݴ͓ͯ͘͠ ͱ 
 fetchBook(id: BookId)
    ͱ͍͏γάωνϟ͔ΒಘΒΕΔ৘ใྔ͕ 
 fetchBook(id: string)
    ʹൺ΂͙ͯͬͱ૿͢
    w ͦΕ͸
    UserId
    Ͱ͸μϝͱΘ͔Δ
    w ͦΕ͸ۭจࣈྻͰ͸μϝͱΘ͔Δ
    w ࣮૷୲౰ऀʹޱ಄Ͱฉ͍ͯճΔඞཁ͕ͳ͍
    w ͜ͷߟ͑ํ͸ܖ໿ϓϩάϥϛϯά ʢ%FTJHO
    CZ
    $POUSBDU
    %C$ͳͲͱ΋ʣ ͷ 
 ํ๏࿦ʹج͍͍ͮͯΔ
    w ಛʹࣄલ৚݅΍ෆม৚݅ʹ֘౰
50. த਎ͷ͋ΔΞϊςʔγϣϯ΁ w ཁ݅ΛܕΞϊςʔγϣϯʹؚΊΔʕʕཁ݅Ξϊςʔγϣϯʹ͢Δ͜ͱͰ 
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51. 5IBOL
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