Ruby | Access Control

Access control is a very important part of the object-oriented programming language which is used to restrict the visibility of methods and member fields to protect data from the accidental modification. In terms of access control, Ruby is different from all other Object Oriented Programming languages.

Important Points about Ruby Access Control:

• The visibility of the class variable and instance is always private.
• Access controls are only applicable to methods.
• We can’t apply any access control to the instance and the class variables.
• The private methods in Ruby can also be inherited just like public and protected methods.

In Ruby, access control work on two conditions:

• First, from where the method is called, i.e inside or outside of the class definition.
• Second, the self-keyword is included or not. Basically, self-keyword is used to point to the current recipient.

In Ruby, it is not necessary for the inheritance to involve in access control, like in C++ access control are used in inheritance. Access control is of three types as shown in the below image:

Public Method

Public Methods are those methods which can be called by anyone. As we know that access control works only on methods, so by default all the methods are public. But still, we can define a public method explicitly using the public keyword. Public methods are generally called outside the class.

Example:

# Ruby program to demonstrate
# the public access control

#!/usr/bin/ruby

# taking a class
class GeeksforGeeks

     # public method without using
     # public keyword
     def geeks_1
         puts "public method geeks_1 is called"
     end

    # using public keyword
    public

     def geeks_2
         puts "public method geeks_2 is called"
     end

     def geeks_3

         puts "public method geeks_3 is called"

         # calling geeks_1 method
         geeks_1

         # calling geeks_1 method using
         # self-keyword
         self.geeks_1
     end
end

# creating the object of
# class GeeksforGeeks
obj = GeeksforGeeks.new

# calling method geeks_1
obj.geeks_1

# calling method geeks_2
obj.geeks_2

# calling method geeks3
obj.geeks_3

Output:

public method geeks_1 is called
public method geeks_2 is called
public method geeks_3 is called
public method geeks_1 is called
public method geeks_1 is called

Private Method

Private methods are those methods which are not accessible outside the class or in other words, private methods are called only inside the class definition. The methods of the class can access private members. In private methods, we do not use the self-keyword. By default, initialize method will be private method. The user cannot make the initialize method as the public method. A private method is defined by using private keyword.

Note: As we know that private methods are strictly restricted for their visibility, only defined class members can access these methods, but they can be inherited by the subclass. A subclass can access them and can override them.

Example:

# Ruby program to demonstrate
# the private access control

#!/usr/bin/ruby

# creating class
class GeeksforGeeks

    # using initialize method
    # it can't be private
    def initialize
        puts "This is the initialize Method"
     end

    # public method
    def geeks_1

             puts "Public geeks_1 Method"
         end

    # using the private keyword to
    # declare a private method
    private

     def geeks_2

         puts "This is Private Method"
     end

end

# creating the object of
# the class GeeksforGeeks
obj = GeeksforGeeks.new

# calling method geeks_1
# (geeks1 method is public method)
obj.geeks_1

# calling private method will give the error
obj.geeks_2

Error:

source_file.rb:41:in `

‘: private method `geeks_2’ called for # (NoMethodError)
Did you mean? geeks_1

This is the initialize Method
Public geeks_1 Method

Protected Method

Protected methods can only be called by objects of the defined class and its subclass. The access of these methods is limited in between the defined class or its subclass. You cannot access protected methods outside the defined class or its subclass. The usage of protected methods is finite. Protected methods are defined using protected keyword.

Example:

# Ruby program to demonstrate
# the protected access control

#!/usr/bin/ruby

class GeeksforGeeks

    # using initialize method
    def initialize

        # calling geeks_2 method
        geeks_2

        # calling geeks_2 method
        # using self-keyword
        self.geeks_2

     end

    # public method
    def geeks_1
         puts " geeks_1 method is called"
     end

    # defining the protected method using
    # protected keyword
    protected

    def geeks_2
         puts " geeks_2 method is called"
    end

end

# creating the object of class GeeksforGeeks
obj = GeeksforGeeks.new

# calling method
obj.geeks_1


# if you will try to call protected method
# using the object of class then it will
# give error
obj.geeks_2

Error:

source_file.rb:45:in `

‘: protected method `geeks_2’ called for # (NoMethodError)
Did you mean? geeks_1

geeks_2 method is called
geeks_2 method is called
geeks_1 method is called

Note:

• The user can call the private and protected methods inside a public method of the same class.

  Example:

  # Ruby program to demonstrate the calling
  # of private and protected method in the
  # public method
  
  class Geeks
  
      # public method
      def method_1
  
       p "Public Method of class Geeks"
  
          # calling protected and private method
          # inside the public method
          method_2
          method_3
      end
  
      # defining the protected method
      protected
  
      def method_2
  
          p "Protected Method of class Geeks"
       end
  
      # defining the private method
      private
  
      def method_3
  
         p "Private Method of class Geeks"
  
       end
  end
  
  # creating an object of class Geeks
  obj = Geeks.new
  
  # calling the public method of class Geeks
  obj.method_1

  Output:

  "Public Method of class Geeks"
  "Protected Method of class Geeks"
  "Private Method of class Geeks"
  

• In general, private methods can’t be inherited in object-oriented programming languages. But in Ruby, private methods can also be inherited just like protected and public methods.

  Example:

  # Ruby program to demonstrate that private
  # method can also be inherited
  
  class Geeks
  
      # public method
      def method_1
  
          p "Public Method of class Geeks"
  
      end
  
      # defining the protected method
      protected
  
      def method_2
  
          p "Protected Method of class Geeks"
       end
  
      # defining the private method
      private
  
      def method_3
  
          p "Private Method of class Geeks"
  
       end
  end
  
  # Sudo class inheriting Geeks class
  class Sudo < Geeks
  
      # public method of Sudo class
      def method_4
  
          p "Public Method of Sudo Class"
  
          # calling all three methods
          # of Geeks class
          method_1
          method_2
          method_3
      end
  end
  
  # creating an object of class Sudo
  obj_sudo = Sudo.new
  
  # calling the public method
  # of class Sudo which will
  # automatically call the private
  # and protected method of Geeks class
  obj_sudo.method_4

  Output:

  "Public Method of Sudo Class"
  "Public Method of class Geeks"
  "Protected Method of class Geeks"
  "Private Method of class Geeks"
  

• The public method can be accessed outside the class in which they are defined. But user can’t access the private and protected methods outside the class in which they were defined.

  Example:

  # Ruby program to demonstrate that private
  # and protected method can't be accessed
  # outside the class even after inheritance
  
  class Geeks
  
      # public method
      def method_1
  
          p "Public Method of class Geeks"
  
      end
  
      # defining the protected method
      protected
  
      def method_2
  
          p "Protected Method of class Geeks"
       end
  
      # defining the private method
      private
  
      def method_3
  
          p "Private Method of class Geeks"
  
       end
  end
  
  # Sudo class inheriting Geeks class
  class Sudo < Geeks
  
      # public method of Sudo class
      def method_4
  
          p "Public Method of Sudo Class"
  
      end
  end
  
  # creating an object of class Sudo
  obj_sudo = Sudo.new
  
  # calling the public method
  # of class Sudo and Geeks
  obj_sudo.method_4
  obj_sudo.method_1
  
  # if you will try to call the protected
  # and private method using the object
  # of class Sudo, then it will give error
  obj_sudo.method_2
  obj_sudo.method_3

  Error:

  source_file.rb:54:in `

  ‘: protected method `method_2’ called for # (NoMethodError)
  Did you mean? method
  method_1
  method_4
  methods

  “Public Method of Sudo Class”
  “Public Method of class Geeks”

• The main difference between the protected and private methods is that protected methods are accessible from inside the class by using an explicit receiver while private methods are not.

  Example:

  # Ruby program to demonstrate that private
  # and protected method can't be accessed
  # outside the class even after inheritance
  
  class Geeks
  
      # public method
      def method_1
  
          p "Public Method of class Geeks"
  
      end
  
      # defining the protected method
      protected
  
      def method_2
  
          p "Protected Method of class Geeks"
       end
  
      # defining the private method
      private
  
      def method_3
  
          p "Private Method of class Geeks"
  
       end
  end
  
  # Sudo class inheriting Geeks class
  class Sudo < Geeks
  
      # public method of Sudo class
      def method_4
  
          p "Public Method of Sudo Class"
  
  
  
          # calling the public method
          # of Geeks class
          method_1
  
          # creating object of class Sudo
          # inside the public method of
          # class Sudo
          obj_inside_sudo = Sudo.new
  
          # calling the protected
          # method of class Geeks
          obj_inside_sudo.method_2
  
          # calling the private
          # method of class Geeks
          # using an explicit receiver
          obj_inside_sudo.method_3 rescue p "You can't Access!"
  
  
  
      end
  end
  
  
  
  # creating an object of class Sudo
  obj_sudo = Sudo.new
  
  # calling the public method
  # of class Sudo
  obj_sudo.method_4

  Output:

  "Public Method of Sudo Class"
  "Public Method of class Geeks"
  "Protected Method of class Geeks"
  "You can't Access!"
  

• To define multiple protected and private methods in a single class, you can use the following syntax:

  class class_name
  
    # this method is public 
    def public_method        
    end  
  
    public :method_1
    
    protected :method_2, :method_3
    
    private :method_4, :method_5  
  
  end