Apa iku struct ing Go?

Question

Accepted Answer

**struct** yaiku tipe komposit sing ngelompokake field-field sing gegandhengan — cara Go kanggo nemtokake tipe data khusus lan nggawe model entitas. Amarga Go ora ana kelas, struct (plus metode) yaiku cara Go nglakoni pemrograman gaya berorientasi obyek.

## Nemtokake lan nggunakake struct

```go
type Person struct {
    Name string     // exported (capitalized) → accessible from other packages
    Age  int
    email string    // unexported (lowercase) → package-private
}

// creating instances
p1 := Person{Name: "Ann", Age: 30}        // named fields (preferred — clear, order-independent)
p2 := Person{"Bob", 25, "bob@x.com"}       // positional (fragile — order matters)
var p3 Person                              // zero value: {"", 0, ""}

p1.Name          // access fields with dot notation
p1.Age = 31      // mutate
```

## Visibility field liwat kapitalisasi

```text
Capitalized field/type/func name → EXPORTED (public, usable outside the package)
lowercase name → unexported (private to the package)
```

Go nggunakake kapitalisasi, ora keyword, kanggo visibility — konvensi khas Go.

## Metode ing struct (OOP Go)

```go
// a method is a function with a RECEIVER (the struct it operates on)
func (p Person) Greet() string {           // value receiver
    return "Hi, I'm " + p.Name
}
func (p *Person) Birthday() {                // pointer receiver — can MODIFY the struct
    p.Age++
}

p1.Greet()       // "Hi, I'm Ann"
p1.Birthday()    // modifies p1 (Go auto-takes the address)
```

Metode nglampirake perilaku menyang struct liwat *receiver*. Receiver pointer (`*Person`) ngliloni metode ngowahi struct; receiver nilai mendapatake salinan.

## Struct yaiku tipe nilai

```go
p1 := Person{Name: "Ann"}
p2 := p1            // COPIES the entire struct (independent)
p2.Name = "Bob"
fmt.Println(p1.Name)   // "Ann" — unchanged (it was a copy)

// pass a pointer to share/modify
func update(p *Person) { p.Name = "X" }
```

Nugasake utawa ngepassi struct **nliyoni** (value semantics) — kanggo babagi utawa ngowahi, gunakake pointer.

## Struct tag (metadata)

```go
type User struct {
    Name  string `json:"name"`           // tags guide encoding/decoding
    Email string `json:"email,omitempty"`
}
```

Tag nglampirake metadata (digunakake dening JSON, DB, perpustakaan validasi) sing dibacok liwat reflection.

## Kenapa iku penting

Struct yaiku cara inti kanggo nggawe model data lan mbangun tipe khusus ing Go — lan digabungake karo metode, struct yaiku cara Go nglakoni pemrograman gaya berorientasi obyek (ora ana kelas).

Mahami nemtokake struct, konvensi visibility **adhedhasar kapitalisasi** (unik ing Go), **value semantics** (nugasake nyliyoni — dadi gunakake pointer kanggo babagi/owahi, kesalahan umum), metode karo receiver nilai vs pointer, lan struct tag (kanggo pemetaan JSON/DB) yaiku kadhanan pandaman kanggo meh kabeh kode Go.

Struct mundhak ing manawa-manawa — domain model, konfigurasi, payload API, struktur data — nggawakna pengetahuan sing perlu lan kanggo-kanggo kanggo ngerjani Go kanthi trep.