Public vs Private vs Protected in Ruby: Key Differences and Usage

In Ruby, public methods can be called by anyone, private methods can only be called within the defining class without an explicit receiver, and protected methods can be called by instances of the defining class or its subclasses, but only with an explicit receiver. These control how and where methods are accessible to enforce encapsulation.

Quick Comparison

Here is a quick table summarizing the key differences between public, private, and protected methods in Ruby.

Access Modifier	Who Can Call?	Receiver Allowed?	Default Visibility	Typical Use Case
public	Anyone	Yes	Yes	Methods meant for all users
private	Only within defining class	No (implicit receiver only)	No	Internal helper methods
protected	Instances of defining class or subclasses	Yes (explicit receiver allowed)	No	Methods shared within family classes

Key Differences

Public methods are the most open. They can be called from anywhere, on any instance, with an explicit receiver. This is the default visibility for methods in Ruby.

Private methods are more restrictive. They can only be called within the class they are defined in, and you cannot use an explicit receiver when calling them—even self is not allowed. This means private methods are purely internal helpers.

Protected methods are a middle ground. They can be called by any instance of the defining class or its subclasses, but only with an explicit receiver. This allows related objects to share sensitive methods without exposing them publicly.

Code Comparison

Here is an example showing how public methods work in Ruby.

ruby

class Person
  def greet
    "Hello!"
  end
end

person = Person.new
puts person.greet

Output

Hello!

Private and Protected Equivalent

This example shows private and protected methods and how they behave differently.

ruby

class Person
  def call_private
    private_method
  end

  def call_protected(other)
    other.protected_method
  end

  private

  def private_method
    "private called"
  end

  protected

  def protected_method
    "protected called"
  end
end

person1 = Person.new
person2 = Person.new
puts person1.call_private
puts person1.call_protected(person2)

Output

private called
protected called

When to Use Which

Choose public when you want methods accessible to everyone, like the main actions of your objects. Use private for internal helper methods that should never be called from outside the class, ensuring encapsulation. Opt for protected when you want to allow related objects (instances of the same class or subclasses) to access certain methods, but keep them hidden from the outside world.

Key Takeaways

Public methods are accessible from anywhere with an explicit receiver.

Private methods can only be called inside the class without an explicit receiver.

Protected methods allow access between instances of the same class or subclasses with an explicit receiver.

Use private for internal helpers, protected for controlled sharing, and public for general API methods.