Exception hierarchy in Ruby - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of exception class inheritance check

What is the output of this Ruby code snippet?

Ruby

puts ZeroDivisionError < StandardError
puts StandardError < Exception
puts Exception < Object

A

true
true
true

B

false
true
true

C

true
false
true

D

true
true
false

💡 Hint

Remember that ZeroDivisionError inherits from StandardError, which inherits from Exception, which inherits from Object.

In Ruby, ZeroDivisionError is a subclass of StandardError, which is a subclass of Exception, and Exception inherits from Object. The < operator checks if the left class is a subclass of the right class.

❓ Predict Output

intermediate

Exception rescue specificity

What will be printed when this Ruby code runs?

Ruby

begin
  raise IOError, 'file error'
rescue StandardError
  puts 'rescued StandardError'
rescue IOError
  puts 'rescued IOError'
end

A rescued IOError

B rescued StandardError

C no output

D RuntimeError

💡 Hint

Consider the order of rescue clauses and inheritance of IOError.

In Ruby, IOError inherits from StandardError. The first rescue clause that matches the exception type is executed. Since rescue StandardError comes before rescue IOError, it catches the IOError first.

🔧 Debug

advanced

Identify the error type raised

What error type will this Ruby code raise when executed?

Ruby

begin
  1 / 0
rescue => e
  puts e.class
end

A ArgumentError

B TypeError

C NoMethodError

D ZeroDivisionError

💡 Hint

Dividing by zero in Ruby raises a specific error.

Dividing an integer by zero in Ruby raises a ZeroDivisionError. The rescue block captures the exception and prints its class.

❓ Predict Output

advanced

Custom exception inheritance check

Given this Ruby code, what is the output?

Ruby

class MyError < StandardError; end
class MySubError < MyError; end

puts MySubError < StandardError
puts MyError < Exception
puts MySubError < Exception

A

true
true
true

B

true
false
true

C

true
true
false

D

false
true
false

💡 Hint

Trace the inheritance chain from subclasses to their ancestors.

Both MyError and MySubError inherit from StandardError, which inherits from Exception. The < operator returns true if the left class is a subclass of the right class.

🧠 Conceptual

expert

Understanding Ruby exception hierarchy root

Which class is the root of all exception classes in Ruby?

A Object

B StandardError

C Exception

D RuntimeError

💡 Hint

Think about which class all exceptions inherit from directly or indirectly.

In Ruby, Exception is the root class for all exceptions. StandardError and other error classes inherit from Exception. Object is the root of all Ruby objects but not specifically exceptions.

Practice

1.

Which class is the root of the exception hierarchy in Ruby?

easy

A. RuntimeError

B. StandardError

C. Exception

D. IOError

Solution

1. Step 1: Understand Ruby's exception hierarchy

   In Ruby, all exceptions inherit from the Exception class, which is the root of the hierarchy.

2. Step 2: Identify the root class

   Other exception classes like StandardError and RuntimeError are subclasses of Exception.

3. Final Answer:

   Exception -> Option C

4. Quick Check:

   Root exception class = Exception [OK]

Hint: Remember: all errors come from Exception root [OK]

Common Mistakes:

• Confusing StandardError as root
• Thinking RuntimeError is root
• Choosing specific error classes instead of root

2.

Which of the following is the correct way to rescue only StandardError exceptions in Ruby?

begin
  # some code
rescue ???
  puts 'Error caught'
end

easy

A. StandardError

B. Exception

C. RuntimeError

D. IOError

Solution

1. Step 1: Understand rescue syntax

   The rescue keyword can specify which exception class to catch by naming it after rescue.

2. Step 2: Choose the correct exception class

   To catch only StandardError exceptions, write rescue StandardError.

3. Final Answer:

   StandardError -> Option A

4. Quick Check:

   Rescue specific error = StandardError [OK]

Hint: Use rescue with exact error class name [OK]

Common Mistakes:

• Using Exception catches too many errors
• Using RuntimeError misses other StandardErrors
• Using IOError catches unrelated errors

3.

What will be the output of this Ruby code?

begin
  raise IOError, 'File error'
rescue StandardError => e
  puts e.class
end

medium

A. StandardError

B. Exception

C. RuntimeError

D. IOError

Solution

1. Step 1: Identify the raised exception

   The code raises an IOError with message 'File error'.

2. Step 2: Check rescue clause

   The rescue catches StandardError and its subclasses. IOError is a subclass of StandardError, so it is caught.

3. Step 3: Output the exception class

   The code prints e.class, which is IOError.

4. Final Answer:

   IOError -> Option D

5. Quick Check:

   Raised error class = IOError [OK]

Hint: Raised error class prints even if rescued [OK]

Common Mistakes:

• Assuming rescue prints StandardError
• Confusing Exception with StandardError
• Thinking RuntimeError is printed

4.

Find the error in this Ruby code snippet:

begin
  raise 'Oops!'
rescue IOError
  puts 'IO error caught'
end

medium

A. The raise statement must specify an exception class

B. The rescue clause will not catch the raised error

C. The rescue clause syntax is incorrect

D. No error; code runs fine

Solution

1. Step 1: Analyze the raised error

   Raising with a string 'Oops!' creates a RuntimeError by default.

2. Step 2: Check rescue clause type

   The rescue only catches IOError, but the raised error is RuntimeError, so it is not caught.

3. Final Answer:

   The rescue clause will not catch the raised error -> Option B

4. Quick Check:

   Rescue type mismatch causes uncaught error [OK]

Hint: Raised error type must match rescue type [OK]

Common Mistakes:

• Thinking rescue catches all errors by default
• Believing string raise is invalid syntax
• Assuming rescue syntax is wrong

5.

You want to catch all exceptions except system-exiting ones like SystemExit and Interrupt. Which class should you rescue to catch most errors but allow system exits?

hard

A. StandardError

B. Exception

C. RuntimeError

D. NoMethodError

Solution

1. Step 1: Understand exception classes for system exit

   Classes like SystemExit and Interrupt inherit directly from Exception, not StandardError.

2. Step 2: Choose rescue class to exclude system exits

   Rescuing StandardError catches most runtime errors but excludes system-exiting exceptions.

3. Step 3: Confirm other options

   Rescuing Exception catches everything including system exits, which is usually not desired.

4. Final Answer:

   StandardError -> Option A

5. Quick Check:

   Rescue StandardError to exclude system exits [OK]

Hint: Rescue StandardError to avoid catching system exits [OK]

Common Mistakes:

• Rescuing Exception catches system exits too
• Choosing RuntimeError misses some errors
• Confusing NoMethodError as base class