Ruby | Constructors - GeeksforGeeks

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

My Personal Notes

Important points to remember about Constructors:

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