Exception hierarchy in Ruby - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to raise a standard error.

Ruby

raise [1], "An error occurred"

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

AStandardError

BException

CRuntimeError

DSyntaxError

Attempts:

3 left

💡 Hint

Common Mistakes

Using Exception directly instead of StandardError.

Using SyntaxError which is for syntax issues.

The StandardError is the default for most errors in Ruby. Using raise StandardError creates a standard error.

2fill in blank

medium

Complete the code to rescue only runtime errors.

Ruby

begin
  # some code
rescue [1] => e
  puts e.message
end

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

ARuntimeError

BStandardError

CException

DNoMethodError

Attempts:

3 left

💡 Hint

Common Mistakes

Using Exception which rescues all exceptions.

Using StandardError which is more general.

To rescue only runtime errors, use rescue RuntimeError. This catches errors of that specific type.

3fill in blank

hard

Fix the error in the code to correctly rescue argument errors.

Ruby

begin
  Integer('abc')
rescue [1] => e
  puts "Error: #{e.message}"
end

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

AStandardError

BArgumentError

CRuntimeError

DTypeError

Attempts:

3 left

💡 Hint

Common Mistakes

Using RuntimeError which does not catch argument errors.

Using TypeError which is different.

The method Integer('abc') raises an ArgumentError when the string is invalid. So rescue ArgumentError to catch it.

4fill in blank

hard

Fill both blanks to create a custom error class inheriting from the correct superclass.

Ruby

class MyError < [1]
  def message
    "Custom error message"
  end
end

raise [2], "Oops!"

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

AStandardError

BException

CMyError

DRuntimeError

Attempts:

3 left

💡 Hint

Common Mistakes

Inheriting from Exception which is too broad.

Raising StandardError instead of the custom error.

Custom errors usually inherit from StandardError. To raise the custom error, use its class name MyError.

5fill in blank

hard

Fill all three blanks to correctly check error class and message.

Ruby

begin
  raise [1], "File not found"
rescue [2] => e
  if e.is_a?([3])
    puts e.message
  end
end

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

ARuntimeError

BStandardError

DArgumentError

Attempts:

3 left

💡 Hint

Common Mistakes

Rescuing ArgumentError which won't catch runtime errors.

Checking for wrong error class in is_a?.

The code raises a RuntimeError, rescues StandardError (which includes runtime errors), and checks if the error is a RuntimeError before printing the message.

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