Apa bedane antarane struct lan class ing Swift?

Question

IT Interview Practice · Accepted Answer

`struct` iku **value type**: dicopy nalika assignment, lan saben salinan iku mandiri. `class` iku **reference type**: assignment nuduhake siji instance, lan loro variabel padha nuding menyang objek sing padha. Bedane siji iki ndadekake paling akeh keputusan desain ing Swift.

## Kepiye cara kerjane

```swift
struct PointS { var x: Int }
class  PointC { var x: Int; init(x: Int) { self.x = x } }

var a = PointS(x: 1)
var b = a          // COPY — b is a separate struct
b.x = 99
print(a.x, b.x)    // => 1 99  (a unaffected)

let c = PointC(x: 1)
let d = c          // SHARE — same instance
d.x = 99
print(c.x, d.x)    // => 99 99 (both changed)
```

## Trade-off

| Aspek | struct (value) | class (reference) |
|--------|----------------|-------------------|
| Semantik copy | salinan mandiri | referensi sing dituduhake |
| Mutasi | butuh `var` / `mutating` | bisa diowahi liwat referensi apa wae |
| Identitas | ora ana (dibandhing miturut nilai) | identitas `===` |
| Inheritance | ora | ya |
| Memori | biasane stack, ora ana ARC | heap, dikelola ARC |

Struct uga butuh `mutating` kanggo ngowahi stored property ing sawijining method, amarga method entuk `self` sing immutable minangka standar.

## Kapan nganggo sing endi

- **Standarane nganggo `struct`** — standard library Swift (`Array`, `String`, `Int`) lan `View` ing SwiftUI kabeh iku value type. Aman kanggo dituduhake ing antarane thread lan ora duwe retain cycle.
- Gunakake `class` nalika sampeyan butuh **shared mutable state**, **identitas**, **inheritance**, utawa interop Objective-C (`NSObject`).

## Kenapa iki penting

Milih value vs reference nemtokake apa owah-owahan ing sawijining panggonan bakal mbocor menyang panggonan liyane. Bug ing endi "ngowahi siji item malah ngowahi kabeh" asale saka reference sharing sing ora dikarepake; kabeh model SwiftUI nganggep view value-type kuwi murah lan bisa dicopy — mula pewawancara mriksa apa sampeyan milih `struct` dhisik.

Aspek	struct (value)	class (reference)
Semantik copy	salinan mandiri	referensi sing dituduhake
Mutasi	butuh `var` / `mutating`	bisa diowahi liwat referensi apa wae
Identitas	ora ana (dibandhing miturut nilai)	identitas `===`
Inheritance	ora	ya
Memori	biasane stack, ora ana ARC	heap, dikelola ARC

Kepiye cara kerjane

Trade-off

Kapan nganggo sing endi

Kenapa iki penting

Pitakon sing gegandhengan