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

Practice - 5 Tasks

1fill in blank

easy

Complete the code to include the Enumerable module in the class.

Ruby

class Collection
  include [1]
end

Drag options to blanks, or click blank then click option'

AEnumerableClass

BEnumerableModule

CEnumerable

DEnumerableMixin

Attempts:

3 left

💡 Hint

Common Mistakes

Using a wrong module name like EnumerableModule or EnumerableClass.

Forgetting to include the module.

The Enumerable module is included by writing include Enumerable inside the class.

2fill in blank

medium

Complete the code to define the required method for Enumerable to work.

Ruby

class Collection
  include Enumerable

  def [1]
    @items.each { |item| yield item }
  end
end

Drag options to blanks, or click blank then click option'

Aeach

Bloop

Citerate

Deach_item

Attempts:

3 left

💡 Hint

Common Mistakes

Defining a method with a different name like each_item or iterate.

Not yielding items inside the method.

The Enumerable module requires the class to define an each method that yields items.

3fill in blank

hard

Fix the error in the code to use Enumerable's map method correctly.

Ruby

collection = Collection.new
collection.instance_variable_set(:@items, [1, 2, 3])
result = collection.[1] { |x| x * 2 }

Drag options to blanks, or click blank then click option'

Amap

Bcollect

Ceach

Dfor_each

Attempts:

3 left

💡 Hint

Common Mistakes

Using each which returns the original collection, not a transformed one.

Using a non-existent method like for_each.

The map method is provided by Enumerable and returns a new array with the results of running the block on each element.

4fill in blank

hard

Complete the code to create a hash with word lengths for words longer than 3 characters.

Ruby

words = ['cat', 'house', 'dog', 'elephant']
lengths = words.inject({}) { |hash, word| word.length [1] 3 ? hash.merge(word: word.length) : hash }

Drag options to blanks, or click blank then click option'

A:

B>

C<

D==

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong separator like comma instead of colon.

Using wrong comparison operators like < or ==.

In Ruby, using Enumerable's inject to build a hash conditionally, merge word: word.length when word.length > 3.

5fill in blank

hard

Fill all three blanks to filter and transform a collection using Enumerable methods.

Ruby

numbers = [1, 2, 3, 4, 5]
result = numbers.[1] { |n| n [2] 2 == 0 }.[3] { |n| n * 10 }

Drag options to blanks, or click blank then click option'

Aselect

B%

Cmap

Dfilter

Attempts:

3 left

💡 Hint

Common Mistakes

Using filter which is not a Ruby Enumerable method.

Using wrong operators instead of modulo.

Using each instead of map for transformation.

select filters elements where the block returns true. The modulo operator % checks for even numbers. Then map transforms each number by multiplying by 10.

Practice

1. What is the main reason Enumerable is considered Ruby's most powerful module?

easy

A. It speeds up your program by using threads.

B. It automatically creates classes for you.

C. It replaces the need for loops entirely.

D. It provides many useful methods once you define each.

Solution

1. Step 1: Understand what Enumerable requires

   The module requires you to define only the each method in your class.

2. Step 2: Recognize the benefit of defining each

   Once each is defined, you get many collection methods like map, select, and reduce for free.

3. Final Answer:

   It provides many useful methods once you define each. -> Option D

4. Quick Check:

   Defining each unlocks Enumerable methods = C [OK]

Hint: Remember: define each, get many methods [OK]

Common Mistakes:

• Thinking Enumerable creates classes
• Believing it manages threads automatically
• Assuming it removes all loops

2. Which of the following is the correct way to include Enumerable in a Ruby class?

easy

A. class MyCollection; include Enumerable; def each; end; end

B. class MyCollection; extend Enumerable; def each; end; end

C. class MyCollection; require Enumerable; def each; end; end

D. class MyCollection; import Enumerable; def each; end; end

Solution

1. Step 1: Recall how modules are added to classes

   To add instance methods from a module, use include.

2. Step 2: Check the syntax for including Enumerable

   The correct syntax is include Enumerable inside the class, and define each method.

3. Final Answer:

   class MyCollection; include Enumerable; def each; end; end -> Option A

4. Quick Check:

   Use include for instance methods = A [OK]

Hint: Use include to add Enumerable instance methods [OK]

Common Mistakes:

• Using extend instead of include
• Trying to require or import modules
• Not defining the each method

3. What will be the output of this Ruby code?

class Numbers
  include Enumerable
  def initialize(nums)
    @nums = nums
  end
  def each
    @nums.each { |n| yield n }
  end
end

nums = Numbers.new([1, 2, 3])
p nums.map { |x| x * 2 }

medium

A. [1, 2, 3]

B. NoMethodError

C. [2, 4, 6]

D. SyntaxError

Solution

1. Step 1: Understand the class and Enumerable inclusion

   The class defines each to yield elements from @nums, so Enumerable methods like map work.

2. Step 2: Trace the map method call

   nums.map { |x| x * 2 } doubles each element: 1*2=2, 2*2=4, 3*2=6.

3. Final Answer:

   [2, 4, 6] -> Option C

4. Quick Check:

   Enumerable map doubles elements = [2, 4, 6] [OK]

Hint: Enumerable methods work if each yields elements [OK]

Common Mistakes:

• Forgetting to define each method
• Confusing map output with original array
• Expecting errors without yield

4. Identify the error in this Ruby class using Enumerable:

class MyList
  include Enumerable
  def initialize(items)
    @items = items
  end
  def each
    @items.each
  end
end

list = MyList.new([1, 2, 3])
p list.select { |x| x > 1 }

medium

A. The initialize method is missing.

B. The each method does not yield elements to the block.

C. select method is not defined in Enumerable.

D. Enumerable cannot be included in custom classes.

Solution

1. Step 1: Check the each method implementation

   The each method calls @items.each but does not yield elements to the block given to MyList's each.

2. Step 2: Understand why this causes an error

   Enumerable methods expect each to yield elements; without yield, methods like select won't work properly.

3. Final Answer:

   The each method does not yield elements to the block. -> Option B

4. Quick Check:

   each must yield elements = D [OK]

Hint: Ensure each yields elements to the block [OK]

Common Mistakes:

• Assuming calling each without yield is enough
• Thinking Enumerable can't be included
• Believing select is not part of Enumerable

5. Given a custom class that includes Enumerable, how can you use Enumerable methods to find the sum of even numbers in a collection stored inside the class?

hard

A. Define each to yield elements, then use select(&:even?).sum on the instance.

B. Override the sum method to filter even numbers manually.

C. Use a for loop outside the class to sum even numbers.

D. Enumerable does not support sum or select methods.

Solution

1. Step 1: Ensure each yields elements from the collection

   Implement the each method to yield each element so Enumerable methods work.

2. Step 2: Use Enumerable methods to filter and sum

   Call select(&:even?) to get even numbers, then sum to add them.

3. Final Answer:

   Define each to yield elements, then use select(&:even?).sum on the instance. -> Option A

4. Quick Check:

   each + select + sum = A [OK]

Hint: Use select(&:even?).sum after defining each [OK]

Common Mistakes:

• Trying to override sum unnecessarily
• Using loops outside instead of Enumerable methods
• Thinking Enumerable lacks sum or select