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Table of contents
1.
Introduction
2.
Defining Ruby Class 
2.1.
Variable In Ruby Class
3.
Defining Ruby Objects
3.1.
Creating Objects in Ruby
4.
Determining Object Type in Ruby
5.
Use #class to Determine the Instance's Class Name in Ruby.
6.
Use #class to Define Classes in Ruby.
7.
Use #is_a? to Determine the Instance's Class Name in Ruby.
8.
Frequently Asked Questions
8.1.
In Ruby, what's the difference between a class and an object?
8.2.
In Ruby, where do you look for the object type?
8.3.
In Ruby, why is everything an object?
8.4.
Is a Ruby function an object?
8.5.
What are Ruby classes?
9.
Conclusion
Last Updated: Mar 27, 2024

Object Class and Object Type in Ruby

Author Mayank Goyal
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Ashwin Goyal
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Introduction

Ruby is a great language for object-oriented programming. Data encapsulation, polymorphism, inheritance, data abstraction, operator overloading, and other properties of an object-oriented programming language. Classes and objects play a vital role in object-oriented programming.

A class is a blueprint for the creation of objects. A class instance is another name for the object. Animals, for example, are a class, and mammals, birds, fish, reptiles, and amphibians are examples. Similarly, the sales department is the class, and the sales data, sales manager, and secretary are the class's objects.

Defining Ruby Class 

When you create a class, you create a blueprint for a data type. This doesn't describe any data, but it does define what the class name signifies: what a class object will be made up of and what operations can be performed on it. A class definition begins with the keyword class, then the class name, and ends with a period. The name must begin with a capital letter, and names with more than one word are run together with each word capitalized and no separating characters, according to the convention.

Syntax:

class Class_name

end

Variable In Ruby Class

Ruby has four different sorts of variables.

Local Variables: The variables defined in a method are known as local variables. Outside of the method, local variables are not accessible. In the next chapter, you'll learn more about the process. Local variables begin with the letter or a lowercase letter.

Instance Variables: For any given instance or object, instance variables are available across methods. As a result, instance variables differ from one object to the next. The at-sign (@) precedes instance variables, followed by the variable name.

Class Variables:  These are a type of variables that can be used across several objects. A class variable is a characteristic of a class that belongs to it. They have the @@ sign before them and the variable name after them.

Global variables: Class variables are not available between classes, although global variables are. You must define a global variable if you want a single variable accessible across all classes. The dollar sign ($) is always present before the global variables.

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Defining Ruby Objects

The default root of all Ruby objects is Object. The object is a descendant of BasicObject, allowing for the creation of alternative object hierarchies. Object methods are available to all classes unless they are expressly overridden. The Kernel module contains object mixes that make the built-in kernel functions globally available. However, the Kernel module defines the instance methods of Object. A class serves as the blueprint for things. Therefore an object is essentially formed from one. The new keyword is used to declare class objects.

Creating Objects in Ruby

Objects represent the class. In Ruby, you can create objects by calling the class's new function. The new method is a special method that comes with the Ruby library. The new method is a member of the class methods group.

Syntax:

object_name=class_name.new

Example:

# class name is the box
class Cricket

# class variable
@@No_of_players = 11

end

# Two Objects of Box class
teamA = Cricktr.new
teamB = Cricket.new

 

Here, Cricket is the class name and No of players in the class variable. The two objects of the box class are teamA and teamB. You use the equal sign (=), then the class name, the dot operator, and the new method.

Determining Object Type in Ruby

In Ruby, there are numerous methods for determining an object's class. The most straightforward method is to ask for it:

ob = "test" #This is an value.
ob.class # This method returns an object representing the String class.

If you're curious about an object's class hierarchy, you can ask any class what its superclass is:

ob.class # String: o is a String object
ob.class.superclass # Object: superclass of String is Object
ob.class.superclass.superclass # nil: Object has no superclass

The right approach to discover an object's "type," a shaky phrase in Ruby, is to use the object.class. Because classes can inherit from other classes, you can use the call method to see if an object is "of a specific type." To see if an object is of type ClassName or derived from it, use is a? (ClassName). In Ruby, type checking is rarely done; instead, objects are evaluated based on their ability to respond to specific methods, a process known as "Duck typing." In other words, there's no need to be picky about the type if it responds to the methods you require. For example, object. is a?(String) is overly restrictive because another class could include methods to convert it to a string or make it behave exactly like String. A better method to test that the object in question does what you want is to use the object.respond to?(:to s).

There are many ways to determine the class of an object; primarily used techniques are:

  • Use #class to Determine the Instance's Class Name in Ruby.
  • Use #class to Define Classes in Ruby.
  • Use #is_a? to Determine the Instance's Class Name in Ruby.

Use #class to Determine the Instance's Class Name in Ruby.

This method returns the class name of the current instance. Consider the following scenario:

'string'.class
=> String
[].class
=> Array
{}.class
=> Hash
String.class
=> Class

Everything in Ruby is an object because it is an object-oriented programming language. The class Class has objects that are also classes. String.class returns Class because of this.

Use #class to Define Classes in Ruby.

class Human; 
end

alice = Human.new
alice.class

Output:

Human

Check out this article - Compile Time Polymorphism

Use #is_a? to Determine the Instance's Class Name in Ruby.

It returns true if the specified object is a class instance; otherwise, it returns false.

'string'.is_a?(String)
=> true
[].is_a?(Hash)
=> false

#is_a also returns true if the object is an instance of any subclasses.

The === operator is defined in the Class class so that it can be used instead of is a?: Numeric === x # true: x is a Numeric

This is a Ruby-only idiom that is likely less readable than the more standard is a? method. In Ruby, every object has a well-defined class that never changes over the object's lifetime. The type of object, on the other hand, is more fluid. An object's type is linked to its class, but it is only one aspect. When we talk about an object's type, we're referring to the behaviors that define it.

 

Another way of putting it is that an object's type is the collection of methods to which it can react. (Because it's not just the names of the methods that matter, but also the types of arguments those methods can accept, this definition becomes recursive.)

 

In Ruby programming, we often don't care about an object's class; all we worry about is if we can call a method on it. Consider the operator <<, for example. This is an append operator in arrays, strings, files, and other I/O-related classes. We might develop a function that provides textual output generically to use this operator. Then any argument that implements << can be used to call our method. We don't care about the argument's class; all that matters is that we may add to it. The response to? the method can be used to test this:

o.respond to? :"<<" # If o has an << operator, this is true.

 

The disadvantage of this approach is that it only verifies the name of a method, not its arguments. Fixnum and Bignum, for example, implement << as a left-shift operator and expect a number rather than a string as an argument. When we use a respond to? test, integer objects appear to be "appendable," but when we append a string to them, we get an error.

Know What is Object in OOPs here in detail.

Frequently Asked Questions

In Ruby, what's the difference between a class and an object?

An object is a data unit. A class defines the type of data it is.

In Ruby, where do you look for the object type?

The right approach to determine an object's "type," a shaky phrase in Ruby, is to use the object. class. Because classes can inherit from other classes, you can use the call method to see if an object is "of a specific type."

In Ruby, why is everything an object?

Except for control structures, almost everything in Ruby is an Object. Whether a method, code block, or operator is or isn't an Object underneath the covers, they are represented as Objects and can be thought of as such.

Is a Ruby function an object?

Methods are not objects in Ruby.

What are Ruby classes?

In Ruby, classes are first-class objects, with each being an instance of the class Class. Typically, a new class is created using the following syntax: class Name # some code explaining the class behavior end. An object of type Class is produced and assigned to a global constant when a new class is created ( Name in this case).

Conclusion

In this article, we learned about ruby classes and objects and how do we creating ruby objects. Lastly, we saw different techniques to determine the type of class of an object.

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