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Ruby constructors

By IncludeHelp Last updated : December 01, 2024

Introduction to Constructors in Ruby

Constructors are one of the most important parts of Object-Oriented programming. A constructor of a class is a unique method which is invoked or called when an object of that particular class is being instantiated. It does not require an explicit statement for their calling.

Purpose of Constructors

The main purpose of constructors is to facilitate initialization to the variables of the class during the process of object creation. Constructors work same as a normal method, they do contain statements, expressions, and method calls.

Constructors in Ruby vs Other Languages

In other object-oriented languages like C++ and Java, the name of class and constructor is used to be the same but in the case of Ruby, the name is different from the name of the class. In Ruby, you can define a constructor with the help of the following syntax,

def initialize
  #expressions
end

Syntax for Defining a Constructor

A constructor returns the object of that class. It is not possible to provide an inheritance to the constructor whereas it is permissible to overload a constructor. The constructors are defined within a class in the following way:

Constructor without arguments

class CLASS_NAME  
    def initialize  
        # expressions  
    end  
    # other methods  
end

The above is a syntax of a constructor with no arguments. Go through the following syntax to understand constructor with arguments,

Constructor with arguments

class CLASS_NAME  
    def initialize(argument list)  
        # expressions  
    end  
    # other methods  
end 

Key Characteristics of Constructors

• Constructors are invoked using the new keyword.
• The new keyword internally calls the initialize method.
• Providing arguments to new passes them to the initialize method.
• Errors occur if arguments provided to new do not match the constructor's parameter list.

Example: Non-Parametric Constructor

Let us understand the example of a non-parametric constructor

=begin
Ruby program to demonstrate constructor 
without parameters
=end

class ClassA
  #non parametric constructor
  def initialize
    for i in 0..10
      puts "Welcome to Includehelp.com"
    end
  end
end

#class instantiation
ClassA.new 

Output

Welcome to Includehelp.com
Welcome to Includehelp.com
Welcome to Includehelp.com
Welcome to Includehelp.com
Welcome to Includehelp.com
Welcome to Includehelp.com
Welcome to Includehelp.com
Welcome to Includehelp.com
Welcome to Includehelp.com
Welcome to Includehelp.com
Welcome to Includehelp.com

You can observe in the above code that when we are giving an explicit call to "new" keyword, it is in return giving an internal call to initialize method.

Example: Parametric Constructor

Now, understand parametric constructor with the help of example given below,

=begin
Ruby program to demonstrate 
constructor with parameters
=end

class ClassA
  #parametric constructor
  def initialize(a,b)
    @instA=a
    @instB=b
  end
  def prnt
    puts "First value is : #{@instA}"
    puts "Second value is : #{@instB}"
  end
end

#class instantiations
ob1=ClassA.new(10,20) 
ob2=ClassA.new(13,200)
ob1.prnt
ob2.prnt

Output

First value is : 10
Second value is : 20
First value is : 13
Second value is : 200

In the above example, you can observe that we are providing values to "new" and "new" is proving those values to initialize method.