Comparable module usage in Ruby - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of the Comparable module in Ruby?

The Comparable module allows objects to be compared using operators like <, <=, ==, >, and >= by defining a single <=> method.

beginner

Which method must be defined in a class to use the Comparable module?

You must define the <=> method (called the spaceship operator) that returns -1, 0, or 1 depending on whether the object is less than, equal to, or greater than another object.

intermediate

How does the <=> method work in the Comparable module?

It compares two objects and returns -1 if the first is less, 0 if equal, and 1 if greater. This single method enables all comparison operators.

intermediate

Example: How to include Comparable in a class and define <code><=></code>?

class Box
  include Comparable
  attr_reader :volume
  def initialize(volume)
    @volume = volume
  end
  def <=>(other)
    volume <=> other.volume
  end
end

This lets you compare Box objects by volume.

advanced

What happens if you include Comparable but do not define <=>?

Ruby will raise a NoMethodError when you try to compare objects because Comparable depends on the <=> method to work.

What does the <=> method return when the first object is greater than the second?

A 1

B -1

C 0

D true

The <=> method returns 1 if the first object is greater than the second.

Which module do you include to get comparison operators by defining only <=>?

A Enumerable

B Comparable

C Kernel

D Math

The Comparable module provides comparison operators when you define the <=> method.

If you want to compare objects by their age attribute, what should <=> return?

A age + other.age

B age == other.age

C age <=> other.age

D age > other.age

The <=> method should return the result of comparing the age attributes using <=>.

What error occurs if Comparable is included but <=> is missing?

A SyntaxError

B ArgumentError

C TypeError

D NoMethodError

Ruby raises a NoMethodError because Comparable requires the <=> method.

Which of these operators is NOT provided by including Comparable?

A ===

B ==

C !=

D <

The === operator is not provided by Comparable; it is used for case equality and pattern matching.

Explain how to use the Comparable module in a Ruby class to enable object comparisons.

Think about what method Comparable needs and what it returns.

Describe what the spaceship operator (<=>) does and why it is important for Comparable.

It's the heart of how Comparable works.