Menene iyakoki na jenetiriko?

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**Iyakon jenetiriko** (`T extends ...`) yana taggara ma nau'in da girman parametar jenetiriko zai iya zama, don ka iya amintaccewa cewa zaka iya amfani da wasu kaddarori ko hanyoyi akan shi. Ba tare da iyaka ba, jenetiriko zai iya zama *komai*, don haka ba za ka iya tunanin cewa akwai wasu kayan jama'a ba. ```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 ``` Iyakon yana da alama na *alkawari*: "`T` koda yaushe zai kasance aƙalla wannan sura," wanda ke baiwa compiler izin kashe `.length` daidai da kiyaye `T` daidai (nau'in da akayi newar shi shi ne ainihin array/string nau'i, ba iyaka ba). ## Iyakoki zuwa mabugi (gaske-gaske gida) ```ts function pluck(obj: T, key: K): T[K] { return obj[key]; } ``` `K extends keyof T` yana tabbatar da cewa `key` shine ainihin dukiya na `obj` — da `T[K]` yana mayar da nau'inta daidai. ## Nau'ikan parametar na tsohuwa ```ts interface Box { value: T; } // T defaults to string if not specified ``` ## Menene ya sa haka ya zama mahimmanci Iyakoki su ne daidaitaccen tsakanin jingina da kiyaye: suna bai da damar ga jenetiriko code da shigar da wuri mafi karami (akwai `.length`, akwai mabugi `K`, ya shimme wasu tushe) yayin da aka ciyar da nau'in takaice na mai kira. Suna da mahimmanci ga abubuwan aiki na fa'ida, ƙirƙirar ablah ajiyya nau'i, da kowane jenetiriko wanda ke bukatan yi wani abu tare da nau'ina parametar.