Ensure for cleanup in Ruby - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Ruby code using ensure?

Consider the following Ruby code snippet. What will it print when run?

Ruby

def test_ensure
  begin
    puts "Start"
    raise "Error occurred"
  ensure
    puts "Cleanup"
  end
end

test_ensure

A Start\nRuntimeError: Error occurred

B Start\nCleanup

C Cleanup\nStart\nRuntimeError: Error occurred

D Start\nCleanup\nRuntimeError: Error occurred

💡 Hint

Remember that ensure runs no matter what, even if an error is raised.

The code prints "Start" first, then raises an error. The ensure block runs next, printing "Cleanup". After that, the error is propagated, causing the RuntimeError message.

❓ Predict Output

intermediate

What value does the method return with ensure?

What will the following Ruby method return when called?

Ruby

def return_test
  begin
    return 10
  ensure
    return 20
  end
end

return_test

A 20

B 10

C nil

D RuntimeError

💡 Hint

The ensure block can override the return value if it has a return statement.

Even though the begin block returns 10, the ensure block's return 20 overrides it, so the method returns 20.

❓ Predict Output

advanced

What is the output and final value of x?

Analyze this Ruby code. What is printed and what is the final value of x after execution?

Ruby

x = 0
begin
  x = 1
  raise "fail"
rescue
  x = 2
ensure
  x = 3
end
puts x

A 1

B 3

C 2

D RuntimeError

💡 Hint

Ensure runs after rescue and can change variable values.

The begin block sets x=1 then raises an error. Rescue sets x=2. Ensure runs last and sets x=3. So x is 3 when printed.

❓ Predict Output

advanced

What error does this code raise?

What error, if any, will this Ruby code raise?

Ruby

def test
  begin
    raise "Oops"
  ensure
    raise "Cleanup error"
  end
end

test

A No error, method returns normally

B RuntimeError: Oops

C RuntimeError: Cleanup error

D SyntaxError

💡 Hint

An error in ensure overrides any previous error.

The first raise triggers "Oops" error, but the ensure block raises "Cleanup error" which overrides the first error. So the final error is "Cleanup error".

🧠 Conceptual

expert

Why use ensure instead of rescue for cleanup?

Which statement best explains why Ruby programmers use ensure blocks for cleanup instead of rescue blocks?

A Ensure runs regardless of whether an exception occurs, guaranteeing cleanup code always executes.

B Rescue runs only if no exception occurs, so it is unreliable for cleanup.

C Rescue blocks run before the main code, so they cannot clean up after it.

D Ensure blocks catch exceptions and prevent program crashes.

💡 Hint

Think about when cleanup code must run.

Ensure blocks always run after the begin block, whether or not an exception was raised, making them ideal for cleanup tasks like closing files or releasing resources.