Menene nau'in `never` kuma ta yaya yake ba da damar fitsari na gaskiya?

Question

Accepted Answer

`never` shine nau'in ƙimomi da **ba sa faruwa kaɗai** — aiki da ba zai komawa kaɗai (ya jefar ko ba ta ɗaki har abada), ko rashin da kayan aiki ya tabbatar ba zai yiwu ba. Ƙauri shine *babu* nau'i: babu ƙimomi da za su iya ba da `never` (sai `never` kanta).

```ts
function fail(msg: string): never { throw new Error(msg); } // never returns
function loop(): never { while (true) {} }
```

## Me take `never` da amfani: fitsari na gaskiya

Lokacin da ka rage ƙungiyar zuwa babu kome, TypeScript yana buga sauran ƙimomi azaman `never`. Kana amfani da wannan don damre kowane hali:

```ts
type Shape =
  | { kind: "circle"; r: number }
  | { kind: "square"; side: number };

function area(s: Shape): number {
  switch (s.kind) {
    case "circle": return Math.PI * s.r ** 2;
    case "square": return s.side ** 2;
    default:
      // if all cases are handled, s is `never` here — assignment OK
      const _exhaustive: never = s;
      return _exhaustive;
  }
}
```

Abin da suke faruwa shine idan wani ya ƙara `{ kind: "triangle"; ... }` zuwa `Shape` amma ya manta hali, `s` a cikin default shine nau'in alwatika (ba `never`), sabili da haka `const _exhaustive: never = s` **ya kasa shuka** — sannan kake gano daidai cire-cire waccan bukatar sabuntawa.

## `never` vs `void`

```ts
function a(): void {}   // returns normally, just no value
function b(): never { throw "x"; } // never returns at all
```

## Me take mahimman haka

`never` yana juye "ko na damre kowe hali?" daga kishin lokacin aiki zuwa tabbacin lokacin shirya.

Shi ne mahimmanci ga sauye-sauye masu amfani da haɗa kasua — ƙara sau kuma kayan aiki zai ƙayyade daidai inda dole ka sabunta.

Me take never da amfani: fitsari na gaskiya

never vs void

Me take mahimman haka

Me take `never` da amfani: fitsari na gaskiya

`never` vs `void`