Introduction to Encapsulation in Ruby

Welcome back! We're now shifting our focus to another essential concept in Object-Oriented Programming (OOP): encapsulation. Encapsulation helps us bundle the data (variables) and the methods that operate on the data into a single unit called a class. It also helps restrict access to some of the object's components.

In this lesson, you will learn how to:

• Define and use encapsulation: This involves hiding the internal state of an object and requiring all interaction to be performed through an object's methods.
• Create getter and setter methods: These methods allow controlled access to the object's properties using Ruby's attr_accessor, attr_reader, and attr_writer methods.

Let's look at the following Ruby example to gain a better understanding:

# Person class with private data members name and age
class Person
  def initialize(name, age)
    @name = name
    @age = age
  end

  # attr_accessor automatically creates getter and setter for :name and :age
  attr_accessor :name, :age
end

# Create a Person object and set the name and age
person = Person.new("Alice", 30)
person.name = "Bob"
person.age = 25

# Get the name and age of the person and print them
puts "Name: #{person.name}, Age: #{person.age}"

In this example, we have a Person class with private data members @name and @age. The attr_accessor method automatically creates getter and setter methods, like name= and age=, for manipulating and accessing these private members.

In contrast if we use attr_reader or attr_writer, we can only create getter or setter methods, respectively. Here's an example:

class Person
  def initialize(name, age)
    @name = name
    @age = age
  end

  # attr_reader creates only getter methods for :name and :age
  attr_reader :name, :age
end

person = Person.new("Alice", 30)
puts "Name: #{person.name}, Age: #{person.age}" # Output: Name: Alice, Age: 30
# person.name = "Bob" # Error: undefined method `name=' for #<Person:0x00007f8b1b

In this example, we can only read the name and age properties of the Person object, but we can't modify them. If we try to set the name property, we'll get an error because the setter method is not available.

Similarly, if we use attr_writer, we can only create setter methods for the properties. Here's an example:

class Person
  def initialize(name, age)
    @name = name
    @age = age
  end

  # attr_writer creates only setter methods for :name and :age
  attr_writer :name, :age
end

person = Person.new("Alice", 30)
person.name = "Bob"
person.age = 25
# puts "Name: #{person.name}, Age: #{person.age}" # Error: undefined method `name' for #<Person:0x00007f8b1b

If we skip using attr_accessor, attr_reader, or attr_writer, and directly access instance variables, we lose control over the data and can't enforce constraints or validations. Encapsulation allows us to protect the object's internal state and provide controlled access to it.