# Referensi Cepat Ruby

*Objek, block, iterator, regex, dan file I/O esensial*

> Source: Ruby Documentation (ruby-lang.org) · MIT

## Dasar

### Hello World

```
puts "Hello, World!"
print "no newline"
p [1, 2, 3]   # output inspect: [1, 2, 3]
```

### Jalankan Ruby

```
ruby script.rb          # jalankan file
ruby -e 'puts "hi"'    # jalankan inline
irb                     # REPL interaktif
```

### Variabel

| Command | Description |
|---------|-------------|
| `name` | Variabel lokal |
| `@name` | Variabel instance |
| `@@count` | Variabel class |
| `$debug` | Variabel global |
| `MAX_SIZE` | Konstanta (huruf besar menurut konvensi) |

### Tipe

```
42.class         # Integer
3.14.class       # Float
"hello".class    # String
true.class       # TrueClass
nil.class        # NilClass
:symbol.class    # Symbol
```

## String

### Dasar String

```
name = "World"
puts "Hello, #{name}!"        # interpolasi (double quotes)
puts 'No #{interpolation}'    # literal (single quotes)
multi = <<~HEREDOC
  heredoc dengan indent
HEREDOC
```

### Metode String

| Command | Description |
|---------|-------------|
| `.length / .size` | Jumlah karakter |
| `.upcase / .downcase` | Konversi huruf besar/kecil |
| `.strip` | Hapus whitespace awal/akhir |
| `.split(',')` | Pecah menjadi array |
| `.gsub(/pat/, 'rep')` | Substitusi global |
| `.include?('sub')` | Periksa apakah mengandung substring |
| `.start_with?('pre')` | Periksa prefix |
| `.chars / .bytes` | Array karakter / byte |
| `.to_i / .to_f` | Konversi ke integer / float |
| `.freeze` | Buat string tak dapat diubah |

## Array & Hash

### Array

```
arr = [1, "two", :three]
arr << 4                  # push (tambahkan)
arr[0]                    # 1
arr[-1]                   # 4 (elemen terakhir)
arr[1..2]                 # ["two", :three] (slice)
```

### Metode Array

| Command | Description |
|---------|-------------|
| `.push / .pop` | Tambah/hapus dari akhir |
| `.shift / .unshift` | Hapus/tambah dari awal |
| `.flatten` | Ratakan array bersarang |
| `.compact` | Hapus nilai nil |
| `.uniq` | Hapus duplikat |
| `.sort / .reverse` | Urutkan / balik urutan |
| `.map { \|x\| x * 2 }` | Transformasi tiap elemen |
| `.select { \|x\| x > 0 }` | Filter elemen |
| `.reduce(0) { \|sum, x\| sum + x }` | Akumulasikan menjadi satu nilai |

### Hash

```
user = { name: "Alice", age: 30 }   # key symbol
old = { "key" => "value" }           # key string
user[:name]                          # "Alice"
user[:email] = "a@b.com"             # tambah pasangan
user.fetch(:name, "default")         # dengan default
```

### Metode Hash

| Command | Description |
|---------|-------------|
| `.keys / .values` | Array key / nilai |
| `.each { \|k, v\| }` | Iterasi pasangan key-value |
| `.merge(other)` | Gabungkan dua hash |
| `.key?(k) / .value?(v)` | Periksa keberadaan |
| `.select { \|k, v\| }` | Filter pasangan |
| `.transform_values { \|v\| }` | Transformasi semua nilai |

## Alur Kontrol

### Kondisional

```
if score >= 90 then "A"
elsif score >= 80 then "B"
else "C"
end
puts "adult" if age >= 18     # if inline
puts "minor" unless age >= 18 # unless inline
```

### Case / When

```
case status
when :ok then puts "success"
when :error then puts "failed"
when 400..499 then puts "client error"
else puts "unknown"
end
```

### Loop

```
5.times { |i| puts i }
(1..10).each { |n| puts n }
while condition do end
until condition do end
loop { break if done }
```

### Ternary & Logika

```
status = age >= 18 ? "adult" : "minor"
name = input || "default"     # or-assign
name ||= "fallback"           # efek sama
```

## Metode

### Mendefinisikan Metode

```
def greet(name, greeting = "Hello")
  "#{greeting}, #{name}!"
end
greet("Alice")          # "Hello, Alice!"
greet("Bob", "Hi")     # "Hi, Bob!"
```

### Nilai Kembalian

```
def add(a, b)
  a + b    # ekspresi terakhir adalah return implisit
end
def divide(a, b)
  return nil if b == 0
  a.to_f / b
end
```

### Argumen Keyword & Splat

```
def connect(host:, port: 80, **opts)
  puts "#{host}:#{port} #{opts}"
end
def log(*messages)
  messages.each { |m| puts m }
end
```

### Konvensi Metode

| Command | Description |
|---------|-------------|
| `method?` | Mengembalikan boolean (predikat) |
| `method!` | Mengubah receiver (bang method) |
| `self.method` | Definisi class method |

## Class

### Definisi Class

```
class User
  attr_accessor :name, :email
  def initialize(name, email)
    @name = name
    @email = email
  end
end
```

### Inheritance

```
class Admin < User
  def initialize(name, email, level)
    super(name, email)
    @level = level
  end
end
```

### Kontrol Akses

| Command | Description |
|---------|-------------|
| `public` | Default; dapat diakses dari mana saja |
| `private` | Hanya dapat diakses di dalam class |
| `protected` | Dapat diakses dalam class dan subclass |
| `attr_reader` | Buat metode getter |
| `attr_writer` | Buat metode setter |
| `attr_accessor` | Buat getter dan setter |

## Modul

### Mixin

```
module Greetable
  def greet
    "Hello, I'm #{name}"
  end
end
class User; include Greetable; end
```

### Namespace

```
module Payment
  class Processor
    def charge(amount) end
  end
end
p = Payment::Processor.new
```

### Include vs Extend

| Command | Description |
|---------|-------------|
| `include ModName` | Tambahkan sebagai instance method |
| `extend ModName` | Tambahkan sebagai class method |
| `prepend ModName` | Sisipkan sebelum class dalam pencarian metode |

## Block & Iterator

### Sintaks Block

```
[1, 2, 3].each { |n| puts n }        # block satu baris
[1, 2, 3].each do |n|
  puts n                               # block multi-baris
end
```

### Yield

```
def with_logging
  puts "start"
  result = yield
  puts "end"
  result
end
with_logging { expensive_operation }
```

### Proc & Lambda

```
square = Proc.new { |x| x ** 2 }
square.call(5)                   # 25
double = ->(x) { x * 2 }        # lambda
double.call(3)                   # 6
[1, 2, 3].map(&square)           # [1, 4, 9]
```

### Iterator Umum

| Command | Description |
|---------|-------------|
| `.each` | Iterasi tiap elemen |
| `.map / .collect` | Transformasi tiap elemen |
| `.select / .filter` | Pertahankan elemen yang cocok |
| `.reject` | Hapus elemen yang cocok |
| `.reduce / .inject` | Akumulasikan menjadi satu nilai |
| `.each_with_index` | Iterasi dengan indeks |
| `.flat_map` | Map dan ratakan satu level |
| `.any? / .all? / .none?` | Pemeriksaan boolean pada koleksi |

## Regex

### Pencocokan

```
"hello 42" =~ /\d+/         # 6 (posisi kecocokan)
"hello" =~ /\d+/            # nil (tidak cocok)
"hello".match?(/ell/)       # true
md = "age: 30".match(/(\d+)/)
md[1]                        # "30"
```

### Pola Umum

| Command | Description |
|---------|-------------|
| `/^start/` | Dianchor di awal |
| `/end$/` | Dianchor di akhir |
| `/\d+/` | Satu atau lebih digit |
| `/\w+/` | Karakter kata |
| `/\s+/` | Whitespace |
| `/[a-z]+/i` | Case-insensitive |
| `/(group)/` | Capture group |

### Substitusi

```
"hello world".sub(/world/, "Ruby")     # kecocokan pertama
"aabba".gsub(/a/, "x")                 # semua: "xxbbx"
"foo bar".gsub(/(\w+)/) { $1.upcase }  # "FOO BAR"
```

## File I/O

### Baca & Tulis

```
content = File.read("data.txt")
lines = File.readlines("data.txt", chomp: true)
File.write("out.txt", "hello\n")
File.open("log.txt", "a") { |f| f.puts "entry" }
```

### Operasi File

| Command | Description |
|---------|-------------|
| `File.exist?(path)` | Periksa apakah file ada |
| `File.directory?(path)` | Periksa apakah path adalah direktori |
| `File.basename(path)` | Nama file tanpa direktori |
| `File.extname(path)` | Ekstensi file |
| `File.size(path)` | Ukuran file dalam byte |
| `File.delete(path)` | Hapus file |
| `Dir.glob('*.rb')` | Temukan file yang cocok pola |
| `FileUtils.mkdir_p(path)` | Buat direktori secara rekursif |

### CSV & JSON

```
require "json"
data = JSON.parse(File.read("data.json"))
File.write("out.json", JSON.pretty_generate(data))
require "csv"
CSV.foreach("data.csv", headers: true) { |row| puts row["name"] }
```