Apa iku structural typing ing TypeScript?

Question

Accepted Answer

TypeScript nggunakake **structural typing** ("duck typing"): loro jenis cocog yen duwe **wujud sing padha**, ora perlu ngaranan utawa endi dinarasake. Iki beda karo *nominal* typing (Java, C#) nang mana cocog gantung saka naran jenis sing dideklarasikake.

```ts
interface Point { x: number; y: number; }

function print(p: Point) { console.log(p.x, p.y); }

// No `: Point` annotation anywhere, but the shape matches:
const obj = { x: 1, y: 2, z: 3 };
print(obj); // ✅ works — obj has x and y (extra z is fine)
```

`obj` ora tau dideklarasikake minangka `Point`, nanging diterimo amarga wujude *structural* penuhi. Properti tambahan dibenan nalika passing variabel sing ana.

## Pengecilan properti berlebihan

```ts
print({ x: 1, y: 2, z: 3 }); // ❌ Error: 'z' does not exist in type 'Point'
```

Object **literals** sing dilewatke langsung entuk "excess property check" sing luwih ketat supaya ketemu typo — nanging yen ditugasake marang variabel dhisik ya lulus. Iki keseimbangan sing disengaja antara fleksibilitas lan methanani kesalahan.

## Apa iku penting

Structural typing ndadeke TypeScript luwes lan ergonomis — sampeyan bisa penuhi interface tanpa nglekseni eksplisit, cocok karo gaya object-literal JavaScript.

Trade-off: jenis sing kebetulan mibar wujud padha bisa saling ganti sanajan konsep ora ana hubungane (sebab wong nggunakake *branded types* yèn kudu kayak nominal-distinctness).