Peta ing Go kumaha cara kerjane?

Question

Accepted Answer

Sebuah **map** iku tabel hash sing built-in ing Go — koleksi teng ora urut saka **pasangan kunci-nilai** kanthi pangolahanne O(1) rata-rata. Iku cara standar kanggo ngenthok kunci menyang nilai.

## Gawe lan nggunakake peta

```go
// create with make
ages := make(map[string]int)    // map from string keys to int values
ages["Ann"] = 30                 // set
age := ages["Ann"]               // get → 30

// or with a literal
scores := map[string]int{
    "math":    90,
    "science": 85,
}

delete(scores, "math")           // remove a key
len(scores)                       // number of entries
```

## Idiom koma-ok — mbedakake "ilang" saka "nol"

```go
// ⚠️ a missing key returns the ZERO VALUE, not an error
value := scores["missing"]       // 0 — but was it stored as 0, or absent? Ambiguous!

// ✅ the comma-ok form tells you if the key EXISTS
value, ok := scores["missing"]
if ok {
    fmt.Println("found:", value)
} else {
    fmt.Println("not present")    // key doesn't exist
}
```

Iki penting banget: jikane akses kunci sing ilang bali nilai nol saka tipe nilai (0, "", nil), dadi sampeyan **ora bisa mbedakake** "kunci ilang" saka "kunci ana kanthi nilai nol" saka nilai dhewe - booleane `, ok` bisa mbedakake.

## Iterasi (urutane ACAK)

```go
for key, value := range scores {
    fmt.Println(key, value)
}
// ⚠️ iteration order is RANDOMIZED — never rely on map order!
// To iterate in order: collect keys into a slice, sort it, then iterate.
```

Go sengaja ngacakake urut iterasi peta (kanggo nyegah kode gumantung marang iku) - jikane sampeyan butuh iterasi sing urut, pesen kunci dhewe.

## Jebakan peta nil

```go
var m map[string]int        // nil map (declared but not initialized)
v := m["x"]                 // ✅ reading is OK → 0
m["x"] = 1                  // 💥 PANIC: assignment to entry in nil map
// must initialize first: m = make(map[string]int)
```

Peta nil bisa dibaca nanging **panik nalika nulis** - sampeyan kudu `make()` iku (utawa nggunakake literal) sadurunge nyimpen.

## Kunci kudu bisa dibandingake

```text
Valid keys: comparable types (string, int, bool, structs of comparable fields, pointers)
Invalid keys: slices, maps, functions (not comparable) → compile error
```

## Mengapa iki penting

Peta iku struktur data Go sing fundamental lan meh tansaya dienggo kanggo ngenthok kunci-nilai lan pangolahan cepet (cache, indeks, nglitung, ngelompok).

Pirang-pirang tingkah laku penting banget kanggo ngerti lan sumber bug sing umum: **idiom koma-ok** (siji-satunggale cara sing dipercaya kanggo cek ana dadi kunci, amarga kunci ilang bali nilai nol), **urut iterasi sing acak** (aja gumantung marang iku dadi - pesen kunci kanggo output sing urut), lan **panik nulis peta nil** (tansaya gawe durung nulis).

ngerti iki - plus yen kunci kudu tipe sing bisa dibandingake - perlu kanggo Go sing bener ing saben dina lan nunjukake rupa-rupa detalilé praktek sing mbedakake dhasar Go sing kuat lan sering katon ing wawancara.