Class.new for dynamic class creation in Ruby

Introduction

Class.new lets you create a new class on the fly without naming it right away. This helps when you want a quick, custom class without writing a full class definition.

When you need a simple class for a one-time use.

When you want to create many similar classes dynamically.

When you want to add methods or behavior to a class quickly.

When you want to avoid cluttering your code with many class names.

When experimenting or testing small pieces of code.

Syntax

Ruby

my_class = Class.new(superclass = Object) do
  # methods and definitions here
end

You can pass a superclass to inherit from, or leave it blank to inherit from Object.

The block defines methods and behavior inside the new class.

Examples

This creates a new class named MyClass with a method greet that returns "Hello!".

Ruby

MyClass = Class.new do
  def greet
    "Hello!"
  end
end

Here, Dog inherits from Animal and overrides the speak method.

Ruby

Animal = Class.new do
  def speak
    "..."
  end
end

Dog = Class.new(Animal) do
  def speak
    "Woof!"
  end
end

This creates an unnamed class, makes an object, and calls its method.

Ruby

anonymous = Class.new do
  def info
    "I am anonymous"
  end
end

obj = anonymous.new
puts obj.info

Sample Program

This program creates a Greeter class dynamically with a greet method. Then it creates an object and prints a greeting.

Ruby

Greeter = Class.new do
  def greet(name)
    "Hello, #{name}!"
  end
end

g = Greeter.new
puts g.greet("Alice")

Important Notes

You can assign the new class to a constant to use it later by name.

Classes created this way behave like normal classes.

Use this technique to keep your code flexible and DRY (Don't Repeat Yourself).

Summary

Class.new creates a new class dynamically.

You can add methods inside the block.

It helps make quick, custom classes without writing full class definitions.