Class.new for dynamic class creation in Ruby - Step-by-Step Execution

Concept Flow - Class.new for dynamic class creation

Call Class.new

↓

Create new anonymous class

↓

Optionally add methods inside block

↓

Assign class to variable

↓

Create instances with .new

↓

Use instances as normal objects

This flow shows how calling Class.new creates a new class dynamically, optionally adding methods, then assigning it to a variable to create instances.

Execution Sample

Ruby

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

Creates a new class with a greet method, makes an instance, and prints the greeting.

Execution Table

Step	Action	Evaluation	Result
1	Call Class.new with block	Creates new anonymous class	Class object assigned to MyClass
2	Define method greet inside block	Method added to new class	MyClass has greet method
3	Call MyClass.new	Creates instance of MyClass	obj is instance of MyClass
4	Call obj.greet	Runs greet method	Returns string "Hello!"
5	puts output	Prints to console	Hello!

💡 Program ends after printing greeting

Variable Tracker

Variable	Start	After Step 1	After Step 3	Final
MyClass	nil	Class object (anonymous class)	Class object	Class object
obj	nil	nil	Instance of MyClass	Instance of MyClass

Key Moments - 3 Insights

Why do we assign Class.new to a variable?

Assigning the new class to a variable like MyClass lets us create instances and call methods on it later, as shown in execution_table step 1 and 3.

How does the block inside Class.new add methods?

The block runs in the context of the new class, so defining methods inside it adds them to the class, as seen in step 2.

What type is obj after MyClass.new?

obj is an instance of the dynamically created class MyClass, confirmed in step 3 and tracked in variable_tracker.

Visual Quiz - 3 Questions

Look at the execution_table, what is the result of calling obj.greet at step 4?

A "Hello!"

B An error

C nil

D Class object

💡 Hint

Check execution_table row 4 where obj.greet returns "Hello!"

At which step is the new class assigned to MyClass?

A Step 4

B Step 3

C Step 1

D Step 2

💡 Hint

See execution_table row 1 where Class.new returns the class assigned to MyClass

If we remove the block from Class.new, what happens to the greet method?

A It is still defined

B It is not defined

C An error occurs immediately

D The class cannot be created

💡 Hint

Methods are added inside the block as shown in step 2; without the block, no methods are added

Concept Snapshot

Class.new creates a new anonymous class dynamically.
You can add methods inside a block passed to Class.new.
Assign the class to a variable to use it later.
Create instances with .new on that variable.
Instances behave like normal objects of that class.

Full Transcript

This example shows how Ruby's Class.new method creates a new class dynamically. First, Class.new is called with a block that defines a greet method. This creates an anonymous class with that method. The class is assigned to the variable MyClass. Then, calling MyClass.new creates an instance obj of that class. Calling obj.greet runs the greet method and returns "Hello!". Finally, puts prints the greeting. Variables MyClass and obj change from nil to class and instance respectively. This dynamic class creation lets you build classes on the fly and use them like normal classes.