Saturday, 23 May 2015

Scope and Access modifiers in Ruby


Access modifiers (or access specifiers) are keywords in object-oriented languages that set the accessibility of classes, methods, and other members.

Access modifiers set the visibility of methods and member fields. Ruby has three access modifiers: public, protected and private. In Ruby, all data members are private. Access modifiers can be used only on methods. Ruby methods are public, unless we say otherwise. The scope of the methods is until another scope comes i.e. when we write private all the methods below it are private until any other scope (i.e. protected or public).

NOTE: Ruby does not apply any access control over instance and class variables.

Public Methods: Public methods can be called by anyone. Methods are public by default except for initialize, which is always private.

Private Methods: Private methods cannot be accessed, or even viewed from outside the class. Only the class methods can access private members.

Protected Methods: A protected method can be invoked only by objects of the defining class and its subclasses. Access is kept within the family.

  • The public methods can be accessed from inside the definition of the class as well as from the outside of the class.
  • The difference between the protected and the private methods is subtle. Neither can be accessed outside the definition of the class.
  • They can be accessed only within the class itself and by inherited or parent classes.

Example:

# define a class
class Box
# constructor method
def initialize(w,h)
 @width, @height = w, h
end

# instance method by default it is public
def getArea
 getWidth * getHeight
end

# define private accessor methods
private

def getWidth
 @width
end

def getHeight
 @height
end

protected

def printArea
 @area = getWidth * getHeight
 puts "Big box area is : #@area"
end
end

# create an object
box = Box.new(10, 20)

# call instance methods
a = box.getArea
puts "Area of the box is : #{a}"

#try to call private methods
w = box.getWidth

puts "Width of the box is : #{w}"

# try to call protected or methods
box.printArea

OUTPUT:

Area of the box is : 200

access_modifiers.rb:39:in `<main>': private method `getWidth' called for #<Box:0x93ee654 @width=10, @height=20> (NoMethodError)


References:





No comments:

Post a Comment