Utility types kama Partial, Pick na Omit ni nini?

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**Utility types** ni aina za jenerika za kujenga ambazo hubadilisha aina zilizopo, kwa hiyo unachota aina mpya badala ya kuzifafanua tena. Zinakuhifadhi aina kwa DRY na kuendeana na chanzo chao. ```ts interface User { id: number; name: string; email: string; age: number; } Partial; // all properties optional → for update payloads Required; // all properties required Readonly; // all properties readonly Pick; // { id, name } — keep only these Omit; // everything except id → for create payloads ``` ## Kwa nini kuchota ni bora kuliko kudefini tena ```ts // Update endpoint: accept any subset of fields function update(id: number, changes: Partial) { ... } update(1, { name: "New" }); // ✅ only the fields you change // Create endpoint: everything except the server-generated id type CreateUser = Omit; ``` Ikiwezekana kuongeza sehemu kwa `User`, zote hizi zinabadilika kiotomatiki — hakuna ufafanuzi wa pili kusahau. ## Zaidi ya yenye manufaa ```ts Record; // { [key: string]: number } — dictionaries ReturnType; // the return type of a function Parameters; // tuple of a function's parameter types NonNullable; // string (strips null/undefined) Extract; Exclude; // filter members of a union ``` ## Kwa nini ina maana Utility types hukuruhusu kueleza mahusiano kati ya aina ("fomu ya kuunda ni mtumiaji bila id") kwa njia inayobainisha. Zinapunguza kurudia, zinahifadhi aina zilizochotwa kiotomatiki ziwe thabiti na chanzo chao, na zipo mahali pamoja katika misimbo ya kweli — hasa `Partial` kwa updates, `Omit`/`Pick` kwa DTOs, na `Record` kwa ramani.