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

Let me explain Private and protected methods work a little differently in Ruby than in most other programming languages. Suppose you have a class called Foo and a subclass SubFoo . In languages like Java, SubFoo has no access to any private methods defined by Foo . As seen in the Solution, Ruby provides no way to hide a class’s methods from its sub- classes. In this way, Ruby’s private works like Java’s protected.

Suppose further that you have two instances of the Foo class, a and b. In languages like Java, a and b can call each other’s private methods. In Ruby, you need to use a protected method for that. This is the main difference between private and protected methods in Ruby.

class Foo
  private
  def pri
    'hey I am private of Foo'
  end

  protected
  def prot
    'Hey I am protected of Foo'
  end
end

Now subclass of Foo

class SubFoo < Foo
  def call_pri_of_foo
    pri
  end

  def call_prot_of_foo
    prot
  end
end

Now calling the accessors within SubFoo

 > sub_foo = SubFoo.new
 => # 
 > sub_foo.call_pri_of_foo
 => "hey I am private of Foo" 
 > sub_foo.call_prot_of_foo
 => "Hey I am protected of Foo"

Up to here; there seem to be no difference

next_sub_foo = SubFoo.new
 => #

def next_sub_foo.access_private(child_of_sub_foo)
  child_of_sub_foo.pri
end

def next_sub_foo.access_protected(child_of_sub_foo)
  child_of_sub_foo.prot
end

Now calling the accessor

> next_sub_foo.access_private(sub_foo)
# => NoMethodError: private method `pri' called for #

but it can access the protected methods of its siblings

> next_sub_foo.access_protected(sub_foo)
# => "Hey I am protected of Foo"

You can also see @tenderlove's blog for more clear picture http://tenderlovemaking.com/2012/09/07/protected-methods-and-ruby-2-0.html