Rescue modifier (inline form) in Ruby - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of rescue modifier with division by zero

What is the output of this Ruby code?

result = 10 / 0 rescue "error"
puts result

Ruby

result = 10 / 0 rescue "error"
puts result

A 0

B Infinity

C error

D ZeroDivisionError

💡 Hint

The rescue modifier catches exceptions and returns the rescue value instead.

The division by zero raises an exception, but the rescue modifier catches it and returns the string "error".

❓ Predict Output

intermediate

Rescue modifier with method call

What will this Ruby code print?

def greet(name)
  "Hello, #{name}!"
end

message = greet(nil) rescue "No greeting"
puts message

Ruby

def greet(name)
  "Hello, #{name}!"
end

message = greet(nil) rescue "No greeting"
puts message

A Hello, nil!

B No greeting

C TypeError

D Hello, !

💡 Hint

Passing nil to string interpolation does not raise an error.

The method returns "Hello, nil!" because #{nil} becomes "nil". No exception occurs, so rescue is not triggered.

❓ Predict Output

advanced

Rescue modifier with multiple expressions

What is the output of this Ruby code?

value = (1 + 2; raise 'fail') rescue 'rescued'
puts value

Ruby

value = (1 + 2; raise 'fail') rescue 'rescued'
puts value

A SyntaxError

B 3

C fail

D rescued

💡 Hint

The raise happens after 1 + 2, triggering rescue.

The expression raises an exception, so the rescue modifier returns 'rescued'.

❓ Predict Output

advanced

Rescue modifier with method returning nil

What will this Ruby code output?

def maybe_fail
  nil
end

result = maybe_fail rescue "error"
puts result.nil?

Ruby

def maybe_fail
  nil
end

result = maybe_fail rescue "error"
puts result.nil?

A true

B false

C error

D NoMethodError

💡 Hint

No exception is raised, so rescue is not triggered.

The method returns nil normally, so result is nil and result.nil? returns true.

❓ Predict Output

expert

Rescue modifier with chained method calls and exception

What is the output of this Ruby code?

class Box
  def initialize(value)
    @value = value
  end
  def unwrap
    @value or raise "Empty"
  end
end

box = Box.new(nil)
result = box.unwrap rescue "rescued"
puts result

Ruby

class Box
  def initialize(value)
    @value = value
  end
  def unwrap
    @value or raise "Empty"
  end
end

box = Box.new(nil)
result = box.unwrap rescue "rescued"
puts result

A NoMethodError

B rescued

C nil

D Empty

💡 Hint

unwrap raises if @value is nil, rescue catches it.

unwrap raises "Empty" because @value is nil, rescue modifier catches and returns "rescued".

Practice

1. What does the rescue modifier do in Ruby when used like value = 10 / x rescue 0?

easy

A. It ignores the division and returns nil

B. It always returns 10 divided by x

C. It returns 0 if dividing by x causes an error

D. It raises an error if x is zero

Solution

1. Step 1: Understand the rescue modifier usage

   The rescue modifier catches exceptions raised by the expression before it and returns the value after rescue if an error occurs.

2. Step 2: Apply to the example

   If 10 / x raises an error (like division by zero), the rescue modifier returns 0 instead of crashing.

3. Final Answer:

   It returns 0 if dividing by x causes an error -> Option C

4. Quick Check:

   rescue modifier returns fallback on error [OK]

Hint: Rescue modifier returns fallback if error happens [OK]

Common Mistakes:

• Thinking rescue modifier prevents all errors
• Assuming it always returns the original expression
• Confusing rescue modifier with if-else

2. Which of the following is the correct syntax for using the rescue modifier inline in Ruby?

easy

A. result = some_method rescue fallback_value

B. result = rescue some_method fallback_value

C. result = some_method ? rescue fallback_value

D. result = some_method else rescue fallback_value

Solution

1. Step 1: Recall the rescue modifier syntax

   The rescue modifier is placed after an expression, followed by the fallback value, like expression rescue fallback.

2. Step 2: Match with options

   Only result = some_method rescue fallback_value matches this syntax correctly: result = some_method rescue fallback_value.

3. Final Answer:

   result = some_method rescue fallback_value -> Option A

4. Quick Check:

   Correct rescue modifier syntax = result = some_method rescue fallback_value [OK]

Hint: Rescue modifier goes after expression, then fallback [OK]

Common Mistakes:

• Placing rescue before the expression
• Using question marks or else with rescue modifier
• Confusing rescue modifier with rescue block

3. What is the output of this Ruby code?

value = Integer('abc') rescue 'error'
puts value

medium

A. abc

B. error

C. 0

D. Raises an exception

Solution

1. Step 1: Understand Integer conversion with invalid string

   Calling Integer('abc') raises an ArgumentError because 'abc' is not a valid number.

2. Step 2: Apply rescue modifier

   The rescue modifier catches this error and returns the string 'error' instead of crashing.

3. Final Answer:

   error -> Option B

4. Quick Check:

   Invalid Integer conversion rescued to 'error' [OK]

Hint: Rescue returns fallback when conversion fails [OK]

Common Mistakes:

• Expecting the original string as output
• Thinking rescue returns nil by default
• Assuming code raises exception without rescue

4. Identify the error in this Ruby code snippet using rescue modifier:

result = 10 / 0 rescue puts 'Error!'

medium

A. No error; prints 'Error!' and result is nil

B. Syntax error because rescue modifier cannot follow puts

C. Runtime error because rescue modifier is misplaced

D. result will be 0 without error

Solution

1. Step 1: Analyze rescue modifier with puts

   The rescue modifier catches the division by zero error and executes puts 'Error!', which prints the message.

2. Step 2: Understand return value of puts

   puts returns nil, so result is assigned nil after rescue.

3. Final Answer:

   No error; prints 'Error!' and result is nil -> Option A

4. Quick Check:

   Rescue modifier runs puts and assigns nil [OK]

Hint: Rescue modifier returns last expression value after rescue [OK]

Common Mistakes:

• Expecting rescue modifier to return printed string
• Thinking rescue modifier causes syntax error here
• Assuming result keeps original expression value

5. You want to safely convert user input to integer but return -1 if conversion fails. Which code correctly uses rescue modifier for this?

hard

A. num = Integer(user_input) else rescue -1

B. num = rescue Integer(user_input) -1

C. num = Integer(user_input) ? rescue -1

D. num = Integer(user_input) rescue -1

Solution

1. Step 1: Understand rescue modifier placement

   The rescue modifier must come after the expression to catch exceptions and provide fallback.

2. Step 2: Check options for correct syntax and logic

   Only num = Integer(user_input) rescue -1 correctly places rescue after Integer(user_input) and returns -1 on failure.

3. Final Answer:

   num = Integer(user_input) rescue -1 -> Option D

4. Quick Check:

   Correct rescue modifier usage for fallback = num = Integer(user_input) rescue -1 [OK]

Hint: Put rescue after expression, then fallback value [OK]

Common Mistakes:

• Placing rescue before expression
• Using invalid syntax with question marks or else
• Forgetting rescue modifier for error handling