Why blocks are fundamental to Ruby - Challenge Your Understanding

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Ruby code using a block?

Consider the following Ruby code that uses a block with the method times. What will it print?

Ruby

3.times do |i|
  puts i * 2
end

A

1
2
3

B

0
2
4

C

0
1
2

D

2
4
6

💡 Hint

Remember that the block variable i starts at 0 and goes up to one less than the number.

The times method runs the block 3 times with i values 0, 1, and 2. Multiplying each by 2 gives 0, 2, and 4.

🧠 Conceptual

intermediate

Why are blocks important in Ruby?

Which of the following best explains why blocks are fundamental to Ruby?

A Blocks are a way to write comments that the interpreter ignores.

B Blocks are used only for defining classes and modules in Ruby.

C Blocks replace variables and constants in Ruby programs.

D Blocks allow methods to accept chunks of code to be executed later, enabling flexible iteration and callbacks.

💡 Hint

Think about how blocks let you pass code to methods like each or map.

Blocks let you pass a piece of code to a method, which can run it multiple times or at specific moments. This makes Ruby very flexible and expressive.

🔧 Debug

advanced

What error does this Ruby code raise?

Look at this Ruby code using a block. What error will it raise when run?

Ruby

def greet
  yield
  yield('friend')
end

greet do |name|
  puts "Hello, #{name}!"
end

A ArgumentError: wrong number of arguments (given 0, expected 1)

B SyntaxError: unexpected keyword_end

C NoMethodError: undefined method 'yield' for main:Object

D No error, prints 'Hello, !' and 'Hello, friend!'

💡 Hint

Check how many arguments the block expects and how many are passed.

The block expects one argument (name), but the first yield call passes none, causing an ArgumentError.

📝 Syntax

advanced

Which option correctly defines a method that takes a block and calls it twice?

Choose the Ruby code that defines a method twice which calls the given block two times.

A

def twice
  yield
  yield
end

B

def twice
  yield()
  yield()
end

C All of the above

D

def twice(&block)
  block.call
  block.call
end

💡 Hint

Blocks can be called with yield or by passing an explicit block parameter.

All three ways correctly call the block twice. Option C and C use yield, B uses an explicit block parameter.

🚀 Application

expert

What is the output of this Ruby code using blocks and enumerators?

Analyze this Ruby code and select the exact output it produces.

Ruby

result = (1..5).map do |n|
  if n.even?
    n * 2
  else
    n
  end
end

puts result.inspect

A

[1, 4, 3, 8, 5]

B

[2, 4, 6, 8, 10]

C

[1, 2, 3, 4, 5]

D

[1, 8, 3, 16, 5]

💡 Hint

Remember that n.even? checks if a number is even, and map transforms each element.

For even numbers (2 and 4), the block returns n * 2 (4 and 8). For odd numbers, it returns n unchanged. So the array becomes [1, 4, 3, 8, 5].