Ruby | Constructors

Last Updated : 22 Aug, 2018

A constructor is a special method of the class which gets automatically invoked whenever an instance of the class is created. Like methods, a constructor may also contain the group of instructions or a method which will execute at the time of object creation.

Important points to remember about Constructors:

Constructors are used to initialize the instance variables.
In Ruby, the constructor has a different name, unlike other programming languages.
A constructor is defined using the initialize and def keyword.
It is treated as a special method in Ruby.
Constructor can be overloaded in Ruby.
Constructors can’t be inherited.
It returns the instance of that class.

Note: Whenever an object of the class is created using new method, internally it calls the initialize method on the new object. Also, all the arguments passed to new will automatically pass to method initialize.

Syntax:

class Class_Name

   def initialize(parameter_list)

   end

end

Example:

# A Ruby program to demonstrate 
# the working of constructor
  
#!/usr/bin/ruby 
    
# class name  
class Demo 
    
    # constructor 
    def initialize   
        puts "Welcome to GeeksforGeeks!"   
    end   
  
end    
  
# Creating Obejct
Demo.new 

Output:

Welcome to GeeksforGeeks!

Initializing instance variable: Instance variables can be initialized using constructor. Inside the constructor, the initial value to instance variables is provided which can be used further anywhere in the program.

Example:

# Ruby program to initialize instance
# variable using constructor
  
#!/usr/bin/ruby 
  
# class name
class Geeks
      
    # constructor
    def initialize
          
        # instance variable intialzation
        @inst_1 = "GeeksforGeeks"
        @inst_2 = "Sudo Placement"
    end
      
    # display method
    def display
        puts "Value of First instance variable is: #{@inst_1}"
        puts "Value of Second instance variable is: #{@inst_2}"
    end
end
  
# creating object
obj1 = Geeks.new()
  
# calling display method
obj1.display()

Output:

Value of First instance variable is: GeeksforGeeks
Value of Second instance variable is: Sudo Placement

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Important points to remember about Constructors: