# Referensi Cepat Lua

*Tabel, fungsi, metatable, coroutine, modul, pola*

> Source: Lua Reference Manual (lua.org/manual) · MIT

## Dasar

### Hello World

```
print("Hello, Lua!")
```

### Variabel & Penugasan

```
local name = "Lua"      -- local variable
x = 10                  -- global (avoid)
local a, b = 1, 2      -- multiple assignment
a, b = b, a            -- swap values
```

### Komentar

```
-- single line comment
--[[ multi-line
     comment ]]
```

### Operator

| Command | Description |
|---------|-------------|
| `+ - * / %` | Operator aritmatika |
| `//` | Pembagian lantai (5.3+) |
| `^` | Perpangkatan |
| `..` | Penggabungan string |
| `#` | Operator panjang |
| `== ~=` | Sama / tidak sama |
| `and or not` | Operator logika |

## Tipe

### Tipe Data

| Command | Description |
|---------|-------------|
| `nil` | Tidak ada nilai; falsy |
| `boolean` | true atau false |
| `number` | Float presisi ganda (atau integer di 5.3+) |
| `string` | Urutan byte immutable |
| `table` | Array asosiatif (satu-satunya tipe majemuk) |
| `function` | Closure kelas pertama |
| `userdata` | Data C yang dibungkus untuk Lua |
| `thread` | Handle coroutine |

### Pemeriksaan Tipe

```
print(type(42))        -- "number"
print(type("hi"))      -- "string"
print(type(nil))       -- "nil"
print(type({}))        -- "table"
```

## Tabel

### Tabel Gaya Array

```
local fruits = {"apple", "banana", "cherry"}
print(fruits[1])          -- "apple" (1-indexed)
table.insert(fruits, "date")
table.remove(fruits, 2)   -- remove "banana"
print(#fruits)            -- length
```

### Tabel Gaya Kamus

```
local user = {name = "Alice", age = 30}
user.email = "a@b.com"   -- add field
user["name"] = "Bob"     -- bracket access
user.age = nil           -- remove field
```

### Fungsi Tabel

| Command | Description |
|---------|-------------|
| `table.insert(t, v)` | Tambahkan nilai ke array |
| `table.insert(t, i, v)` | Sisipkan di posisi i |
| `table.remove(t, i)` | Hapus elemen di posisi i |
| `table.sort(t [,cmp])` | Urutkan array di tempat |
| `table.concat(t, sep)` | Gabungkan elemen array menjadi string |
| `table.move(t,a,b,c)` | Pindahkan elemen dari a..b ke posisi c |

## Fungsi

### Definisi Fungsi

```
local function add(a, b)
  return a + b
end
local mul = function(a, b) return a * b end
print(add(2, 3))  -- 5
```

### Variadic & Beberapa Nilai Kembalian

```
local function sum(...)
  local s = 0
  for _, v in ipairs({...}) do s = s + v end
  return s
end
local function swap(a, b) return b, a end
local x, y = swap(1, 2)
```

### Closure

```
local function counter()
  local n = 0
  return function()
    n = n + 1; return n
  end
end
local c = counter()
print(c(), c())  -- 1  2
```

## Alur Kontrol

### Kondisional

```
if x > 0 then
  print("positive")
elseif x == 0 then
  print("zero")
else
  print("negative")
end
```

### Perulangan

```
for i = 1, 10 do print(i) end
for i = 10, 1, -1 do print(i) end
for k, v in pairs(tbl) do print(k, v) end
for i, v in ipairs(arr) do print(i, v) end
```

### While & Repeat

```
while x > 0 do x = x - 1 end
repeat
  x = x + 1
until x >= 10
```

## String

### Fungsi String

| Command | Description |
|---------|-------------|
| `string.len(s) / #s` | Panjang string dalam byte |
| `string.sub(s, i, j)` | Substring dari i ke j |
| `string.upper(s)` | Konversi ke huruf kapital |
| `string.lower(s)` | Konversi ke huruf kecil |
| `string.rep(s, n)` | Ulangi string n kali |
| `string.reverse(s)` | Balik string |
| `string.format(fmt, ...)` | Pemformatan gaya printf |
| `string.find(s, pat)` | Temukan pola, kembalikan indeks |
| `string.gsub(s, pat, rep)` | Substitusi global |
| `string.gmatch(s, pat)` | Iterator atas kecocokan pola |

### Karakter Pola

| Command | Description |
|---------|-------------|
| `.` | Karakter apa pun |
| `%a / %A` | Huruf / bukan huruf |
| `%d / %D` | Digit / bukan digit |
| `%w / %W` | Alfanumerik / bukan alfanumerik |
| `%s / %S` | Spasi / bukan spasi |
| `%p` | Tanda baca |
| `* + - ?` | Greedy, greedy, lazy, opsional |

## Metatable

### Menetapkan Metatable

```
local mt = {}
mt.__add = function(a, b)
  return {val = a.val + b.val}
end
local a = setmetatable({val=1}, mt)
local b = setmetatable({val=2}, mt)
local c = a + b  -- c.val == 3
```

### Metamethod Umum

| Command | Description |
|---------|-------------|
| `__index` | Cari key yang hilang (tabel atau fungsi) |
| `__newindex` | Cegat penugasan key baru |
| `__add / __sub / __mul` | Operator aritmatika |
| `__eq / __lt / __le` | Operator perbandingan |
| `__tostring` | Representasi string custom |
| `__len` | Operator # custom |
| `__call` | Panggil tabel sebagai fungsi |
| `__concat` | Operator .. custom |

### OOP dengan Metatable

```
local Dog = {}; Dog.__index = Dog
function Dog.new(name)
  return setmetatable({name=name}, Dog)
end
function Dog:bark() print(self.name.." says Woof") end
local d = Dog.new("Rex"); d:bark()
```

## Coroutine

### Siklus Hidup Coroutine

| Command | Description |
|---------|-------------|
| `coroutine.create(f)` | Buat coroutine dari fungsi |
| `coroutine.resume(co, ...)` | Mulai atau lanjutkan coroutine |
| `coroutine.yield(...)` | Tangguhkan eksekusi, kembalikan nilai |
| `coroutine.status(co)` | "running", "suspended", "dead" |
| `coroutine.wrap(f)` | Buat wrapper coroutine yang bisa dipanggil |

### Contoh Coroutine

```
local function gen(max)
  for i = 1, max do coroutine.yield(i) end
end
local co = coroutine.wrap(gen)
print(co(5))  -- 1
print(co())   -- 2
```

## Modul

### Membuat Modul

```
-- mylib.lua
local M = {}
function M.greet(name)
  return "Hello, " .. name
end
return M
```

### Menggunakan Modul

```
local mylib = require("mylib")
print(mylib.greet("World"))
```

### Library Standar

| Command | Description |
|---------|-------------|
| `math` | Fungsi matematika (sin, random, huge, dll.) |
| `string` | Manipulasi string dan pola |
| `table` | Manipulasi tabel (insert, sort, dll.) |
| `io` | Operasi I/O file |
| `os` | Fasilitas OS (time, clock, execute) |
| `debug` | Antarmuka debug (gunakan dengan hemat) |

## Pola Umum

### Idiom Ternary

```
-- Lua has no ternary; use and/or idiom
local val = condition and "yes" or "no"
-- Caution: fails if "yes" is false/nil
```

### Akses Tabel Aman

```
local function get(t, ...)
  for _, k in ipairs({...}) do
    if type(t) ~= "table" then return nil end
    t = t[k]
  end
  return t
end
get(config, "db", "host")  -- safe nested access
```

### Iterasi dengan ipairs vs pairs

```
-- ipairs: array part, stops at first nil
for i, v in ipairs(arr) do print(i, v) end
-- pairs: all keys (unordered)
for k, v in pairs(tbl) do print(k, v) end
```