Subclass with < operator in Ruby - Step-by-Step Execution

Concept Flow - Subclass with < operator

Define Parent Class

↓

Define Subclass < Parent

↓

Override < operator method

↓

Create Subclass Instances

↓

Compare Instances with <

↓

Return true/false based on logic

This flow shows how to create a subclass that overrides the < operator to compare instances based on custom logic.

Execution Sample

Ruby

class Animal
  attr_reader :age
  def initialize(age)
    @age = age
  end
end

class Dog < Animal
  def <(other)
    age < other.age
  end
end

puts Dog.new(3) < Dog.new(5)

This code defines a subclass Dog that inherits from Animal and overrides the < operator to compare dogs by age.

Execution Table

Step	Action	Evaluation	Result
1	Create Dog instance with age 3	Dog.new(3)	Dog object with age=3
2	Create Dog instance with age 5	Dog.new(5)	Dog object with age=5
3	Compare Dog(3) < Dog(5)	3 < 5	true
4	Print result	puts true	true printed to console
5	End of program	No more code	Program stops

💡 Program ends after printing the comparison result.

Variable Tracker

Variable	Start	After 1	After 2	Final
dog1.age	nil	3	3	3
dog2.age	nil	nil	5	5
comparison_result	nil	nil	true	true

Key Moments - 2 Insights

Why do we override the < method in the subclass?

We override < in the subclass to define how two subclass objects should be compared, as shown in execution_table row 3 where Dog(3) < Dog(5) uses the custom logic.

What does the < operator compare inside the method?

Inside the < method, it compares the age attributes of the two Dog instances, as seen in execution_table row 3 where 3 < 5 is evaluated.

Visual Quiz - 3 Questions

Look at the execution_table, what is the result of Dog.new(3) < Dog.new(5)?

A nil

B false

C true

D Error

💡 Hint

Check execution_table row 3 where the comparison 3 < 5 evaluates to true.

At which step is the Dog instance with age 5 created?

A Step 1

B Step 2

C Step 3

D Step 4

💡 Hint

Look at execution_table row 2 where Dog.new(5) is created.

If we change dog1's age to 6, what would Dog.new(6) < Dog.new(5) return?

A false

B true

C nil

D Error

💡 Hint

Refer to variable_tracker and execution_table row 3 logic: 6 < 5 is false.

Concept Snapshot

Subclass with < operator in Ruby:
- Define subclass with < ParentClass
- Override < method to compare attributes
- Use instance variables for comparison
- Return true/false based on logic
- Enables custom object comparisons

Full Transcript

This example shows how to create a subclass in Ruby that overrides the less-than operator (<). We define a parent class Animal with an age attribute. Then we create a subclass Dog that inherits from Animal. Inside Dog, we override the < method to compare the age of two Dog instances. When we create two Dog objects with ages 3 and 5, comparing them with < calls our custom method, which returns true because 3 is less than 5. The program prints true and then ends.