What are the differences between “private”, “public”, and “protected methods”?

Question

I\'m learning Ruby, and have come up to a point where I am confused.

The book I am using is talking about private, public, and protec

Answer 1

The difference will be on Visibility and how they are affected by Inheritance :

Visibility :

|| Anywhere || Public can be accessed from inside and outside the class.

|| Inside the class || Both Private and Protected can only be accessed from inside the class.

The similarity between Protected and Private :

• Both can be accessed from outside the class through a public method.

The differences between Protected and Private are :

• Private method can not be called with a receiver (not even with #self). UNLESS ... calling a PRIVATE SETTER method. If you try to remove the receiver, Ruby will create a local variable. Self is a must in this case.

• Protected may or may not use self.

• Protected can access another object's protected method that comes from the same class, Private can't.

When it comes to Inheritance :

• Private methods can only be called on subclasses implicitly (simply just the name of the method) but not explicitly (using #self).

• Protected can be called both ways (with or without #self || implicitly or explicitly).

Example with code below :

 class Dog
  attr_accessor :name, :age

  def initialize(n, a)
    self.name = n
    self.age = a
  end

  def accessing_private
    "#{self.name} in human years is #{human_years}. This is secret!"
  end

  def accessing_protected
    "Will this work? " + a_protected_method
  end

  def eat_more_than(other) 
  # accessing other instance's protected method from the same class
    daily_diet < other.daily_diet 
    "#{name} eats more than #{other.name}"
  end

  def boy 
    gender_method("boy") # accessing private setter method
  end

  protected

  def daily_diet 
    age * 2 # the younger, the more they have to eat 
  end

  def a_protected_method
    "Yes, I'm protected!"
  end

  private

  attr_writer :gender

  def gender_method(gender)
    self.gender = gender # private setter method requires self
    "#{name} is a #{gender}"
  end

  def human_years
    age * 8
  end
end

# Create the first object of Dog
blake = Dog.new("Blake", 5)

p blake.accessing_private # "Blake in human years is 16. This is secret!"

p blake.accessing_protected # "Will this work? Yes, I'm protected!"

# Create the second object of Dog
jackson = Dog.new("Jackson", 1)

# Below, protected methods from different objects of the same type/class 
# are proven to share access
p jackson.eat_more_than(blake) # true -> "Jackson eats more than Blake"

# Below, accessing private setter method through a public method.
p blake.boy # Blake is a boy