Why Enumerable is Ruby's most powerful module - Challenge Your Understanding

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of Enumerable#map with a block

What is the output of this Ruby code using Enumerable's map method?

Ruby

numbers = [1, 2, 3, 4]
result = numbers.map { |n| n * 2 }
puts result.inspect

A [2, 4, 6, 8]

B [1, 2, 3, 4]

C 8

D nil

💡 Hint

Enumerable#map applies the block to each element and returns a new array.

The map method takes each element, multiplies it by 2, and returns a new array with these values.

🧠 Conceptual

intermediate

Why does Enumerable require #each?

Why does the Enumerable module require the including class to define the #each method?

A Because Enumerable methods use #each to iterate over elements.

B Because #each is used to sort elements automatically.

C Because #each defines the class constructor.

D Because #each is needed to convert elements to strings.

💡 Hint

Enumerable methods rely on a way to visit each element in a collection.

Enumerable uses the #each method to loop through elements, so it must be defined by the class.

🔧 Debug

advanced

Fix the error when using Enumerable methods

What error will this code produce and why? class Box include Enumerable def initialize(items) @items = items end end box = Box.new([1, 2, 3]) box.map { |x| x * 2 }

A TypeError: can't convert Box to Array

B ArgumentError: wrong number of arguments for map

C NoMethodError: undefined method `each' for #<Box:...>

D SyntaxError: unexpected end-of-input

💡 Hint

Enumerable needs #each to work properly.

The Box class includes Enumerable but does not define #each, so calling map raises NoMethodError.

🚀 Application

advanced

Implement #each to use Enumerable methods

Complete the Box class so that Enumerable methods like #select work correctly on its items.

Ruby

class Box
  include Enumerable
  def initialize(items)
    @items = items
  end

  # Your code here
end

box = Box.new([1, 2, 3, 4])
selected = box.select { |x| x.even? }
puts selected.inspect

A

def each
  yield @items
end

B

def each
  @items.each
end

C

def each
  @items.map { |item| yield item }
end

D

def each
  @items.each { |item| yield item }
end

💡 Hint

The #each method must yield each element to the block.

Defining #each to yield each item allows Enumerable methods to iterate properly.

❓ Predict Output

expert

Output of Enumerable#reduce with initial value

What is the output of this Ruby code using Enumerable's reduce method with an initial value?

Ruby

values = [2, 3, 4]
result = values.reduce(10) { |sum, n| sum + n }
puts result

A 9

B 19

C 24

D TypeError

💡 Hint

Reduce starts with the initial value and adds each element.

Starting from 10, adding 2, then 3, then 4 results in 19.