Protected from super class

They can only be called if the receiver is self or of the same class hierarchy as self

Protected method using self:#

class Animal
  def call
    self.eat
  end
  
  protected
  
  def eat
    p "I eat."
  end
end

animal = Animal.new
animal.call

# Output:
"I eat."

Protected method without using self errors out:#

class Animal

  def call
    eat
  end
  
  protected
  
  def eat
    p "I eat."
  end
end

animal = Animal.new
animal.call

# Output:
main.rb:4:in `call': private method `eat' called for #<Animal:0x00000000cca8a8> (NoMethodError) from main.rb:15:in `<main>'

Private method using self errors out:#

class Animal

  def call
    self.eat
  end
  
  private
  
  def eat
    p "I eat."
  end
end

animal = Animal.new
animal.call

# Output:
main.rb:4:in `call': private method `eat' called for #<Animal:0x00000000cca8a8> (NoMethodError) from main.rb:15:in `<main>'

Protected from superclass cannot be called.#

class Animal
  protected

  def eat
    p "I eat."
  end
end

class Tiger < Animal
end


tiger = Tiger.new
tiger.eat

# Output:
# $ruby main.rb
# main.rb:13:in '<main>': 
# protected method 'eat' called for #<Tiger:0x005596dc122550> (NoMethodError)

Protected from same class cannot be called.#

class Animal
  protected

  def eat
    p "I eat."
  end
end

animal = Animal.new
animal.eat

# Output:

# main.rb:10:in `<main>': protected method `eat' called for #<Animal:0x000000023739b0> (NoMethodError)                                                          