ruby-oop

# Ruby Object-Oriented Programming

Master Ruby's elegant object-oriented programming features. Ruby is a pure object-oriented language where everything is an object.

## Class Definition

### Basic Class Structure

```ruby
class Person
  # Class variable (shared across all instances)
  @@count = 0

  # Constant
  MAX_AGE = 150

  # Class method
  def self.count
    @@count
  end

  # Constructor
  def initialize(name, age)
    @name = name  # Instance variable
    @age = age
    @@count += 1
  end

  # Instance method
  def introduce
    "Hi, I'm #{@name} and I'm #{@age} years old"
  end

  # Attribute accessors (getter and setter)
  attr_accessor :name
  attr_reader :age      # Read-only
  attr_writer :email    # Write-only
end

person = Person.new("Alice", 30)
puts person.introduce
person.name = "Alicia"
```

### Method Visibility

```ruby
class BankAccount
  def initialize(balance)
    @balance = balance
  end

  # Public methods (default)
  def deposit(amount)
    @balance += amount
    log_transaction(:deposit, amount)
  end

  def balance
    format_currency(@balance)
  end

  # Protected methods - callable by instances of same class/subclass
  protected

  def log_transaction(type, amount)
    puts "[#{type}] #{amount}"
  end

  # Private methods - only callable within this instance
  private

  def format_currency(amount)
    "$#{amount}"
  end
end
```

## Inheritance

### Single Inheritance

```ruby
class Animal
  def initialize(name)
    @name = name
  end

  def speak
    "Some sound"
  end
end

class Dog < Animal
  def speak
    "Woof! My name is #{@name}"
  end

  # Call parent method with super
  def introduce
    super  # Calls parent's speak method
    puts "I'm a dog"
  end
end

dog = Dog.new("Buddy")
puts dog.speak
```

### Method Override and Super

```ruby
class Vehicle
  def initialize(brand)
    @brand = brand
  end

  def start_engine
    puts "Engine starting..."
  end
end

class Car < Vehicle
  def initialize(brand, model)
    super(brand)