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MisakiSoeda
April 23, 2025
Programming
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TypeScriptのextends
MisakiSoeda
April 23, 2025
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Transcript
!.JTBLJ4PFEB 5ZQF4DSJQUͷFYUFOET .JUBUT
.JTBLJ4PFEB ൃදऀ גࣜձࣾ#PPL-JWF ٕज़։ൃຊ෦γεςϜ։ൃ෦ετΞ։ൃνʔϜ ϑϩϯτΤϯυΤϯδχΞ 5ZQF4DSJQUͰझຯͰόοΫΤϯυॻ͍ͨΓ͍ͯ͠Δ 5ZQF4DSJQU͕͖ʂ ͷ54,BJHJ͔ΒελοϑΛ͍ͯ͠Δ
ͳͥ͜ͷςʔϚʹͨ͠ͷ͔
ʮܕ҆શͬͯɺͲ͏ਂ۷Γ͢ΔΜͩΖ͏ʁʯ w UZQFDIBMMFOHFTʹઓΛ࢝ΊΔʂ w UZQFDIBMMFOHFTΛ௨ͯ͠ؾ͍ͮͨͷ͕ɺܕϨϕϧͰͷߜΓࠐΈૢ࡞͕ܕ҆ શੑΛܶతʹߴΊͯ͘ΕΔͱ͍͏͜ͱɻ w ಛʹFYUFOETΛͬͨܕૢ࡞͕ҹతͰͨ͠ɻ
FYUFOETͷجຊ
FYUFOETͷجຊ w ܕҾ w Ϋϥεͷܧঝ
FYUFOETͷجຊ w ܕҾɹˡͪ͜Βͷ͓ w Ϋϥεͷܧঝ
FYUFOETͷجຊ T extends U ? X : Y w FYUFOETʮܕ͕݅Λຬ͍ͨͯ͠Δ͔ʁʯΛஅ͢Δ݅ܕͷΩʔߏจɻ
w ଞͷUZQFPGJO͕࣮ߦ࣌ͷʹج͍ͮͯܕΛߜΓࠐΉͷʹର͠ɺ FYUFOETΛͬͨ݅ܕ ʮܕͦͷͷ͚ͩΛݟͯॲཧΛ͚Δʯ७ਮͳܕϨϕϧͷذͰ͢ɻ
ྫ6OJPOܕͷϑΟϧλϦϯά త6OJPO͔Βಛఆͷܕ͚ͩநग़ type OnlyStrings<T> = T extends string ? T
: never; type Mixed = "hello" | 42 | "world"; type JustStrings = OnlyStrings<Mixed>; // "hello" | "world" 6OJPOܕʹରͯ͠5FYUFOETʜͱॻ͘ͱɺ֤ߏཁૉʹରͯ͠ݸผʹධՁ͞ ΕΔlzͱ͍͏༷͕͋Γ·͢ɻ
ྫΦϒδΣΫτͷܕΛಛఆ͢Δ తಛఆͷϓϩύςΟΛ࣋ͭܕ͚ͩΛநग़ type Event = | { type: "click"; x:
number } | { type: "scroll"; y: number }; type ExtractByType<T, K extends string> = T extends { type: K } ? T : never; type ClickEvent = ExtractByType<Event, "click">; // => { type: "click"; x: number }
ྫFYUFOETͷ͍ํʢ੍ˍ݅ܕʣ // ੍ͱͯ͠ͷextends function logLength<T extends { length: number }>(value:
T) { console.log(value.length); } // ݅ܕͱͯ͠ͷextends type OnlyStrings<T> = T extends string ? T : never;
݅ܕͰͷFYUFOETͷϝϦοτ w ܕͷ҆શੑ্͕ʢ༧ظ͠ͳ͍ܕΛ͚Δʣ w ॊೈͳܕૢ࡞͕Ͱ͖ΔʢܕϨϕϧͰ fi MUFSNBQ͕Մೳʣ w ܕਪ͕ਖ਼֬ʹͳΔʢิ͕ޮ͖͘͢ͳΔʣ
·ͱΊ
·ͱΊ w ܕϨϕϧͷૢ࡞ܕ҆શੑͷ伴ʂ w ݅ܕʹΑΔFYUFOETɺܕͷذɾબʹڧྗɻ w UZQFDIBMMFOHFTͰɺܕͷײ֮Λ͑Δͷ͓͢͢Ίʂ