Apa iku generic constraints?

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A **generic constraint** (`T extends ...`) mbatesi tipe apa sing bisa dadi parameter generic, supaya sampeyan bisa nggunakake properti utawa metode tartamtu ing nggone kanthi aman. Tanpa constraint, generic bisa dadi *apa wae*, dadi sampeyan ora bisa nganggep yen duwe anggota apa wae. ```ts // ❌ without a constraint, you can't access .length — T might be a number function longestBad(a: T, b: T) { return a.length > b.length ? a : b; // Error: 'length' does not exist on 'T' } // ✅ constrain T to things that HAVE a length function longest(a: T, b: T): T { return a.length > b.length ? a : b; } longest("abc", "de"); // ✅ strings have length longest([1, 2], [3]); // ✅ arrays have length longest(1, 2); // ❌ numbers have no length ``` Constraint yaiku *janji*: "`T` bakal tansah duwe paling ora bentuk iki," sing ngidini compiler ngidini `.length` nanging tetep menjaga `T` presisi (tipe balik yaiku tipe array/string nyata, dudu constraint). ## Membatesi menyang kunci (sangat umum) ```ts function pluck(obj: T, key: K): T[K] { return obj[key]; } ``` `K extends keyof T` njamin `key` yaiku properti nyata saka `obj` — lan `T[K]` mbalekake tipe pass-an nggone. ## Parameter tipe default ```ts interface Box { value: T; } // T defaults to string if not specified ``` ## Mengapa penting Constraints yaiku keseimbangan antarane flexibility lan safety: padha idin kode generic ngandelake bentuk minimal (duwe `.length`, duwe kunci `K`, extends sawetara base) nalika nglestari tipe spesifik panggilan. Padha penting banget kanggo fungsi utilitas, akses obyek type-safe, lan generic apa wae sing kudu *gawe* samusuyan karo parameter tipe nggone.