Multiple rescue clauses in Ruby

Introduction

Sometimes, different errors need different ways to fix them. Multiple rescue clauses let you handle each error separately.

When you want to handle different errors in different ways.

When your code might fail for several reasons and you want clear fixes.

When you want to show different messages for different problems.

Syntax

Ruby

begin
  # code that might cause errors
rescue ErrorType1
  # handle ErrorType1
rescue ErrorType2
  # handle ErrorType2
else
  # runs if no error
ensure
  # always runs
end

You can have many rescue clauses to catch different error types.

The ensure block runs no matter what, even if there is an error.

Examples

This code catches division by zero specifically, and any other error generally.

Ruby

begin
  1 / 0
rescue ZeroDivisionError
  puts "Can't divide by zero!"
rescue StandardError
  puts "Some other error happened."
end

Different errors from file operations are handled separately.

Ruby

begin
  file = File.open('missing.txt')
rescue Errno::ENOENT
  puts "File not found!"
rescue IOError
  puts "IO error happened!"
end

Sample Program

This program asks for a number and divides 10 by it. It handles zero division and invalid input separately.

Ruby

begin
  puts "Enter a number:"
  num = Integer(gets.chomp)
  result = 10 / num
  puts "10 divided by your number is #{result}"
rescue ZeroDivisionError
  puts "Oops! You can't divide by zero."
rescue ArgumentError
  puts "That's not a valid number."
end

Important Notes

Order matters: Ruby checks rescue clauses from top to bottom and stops at the first match.

Use specific error classes first, then more general ones later.

You can use rescue without specifying an error to catch all StandardError exceptions.

Summary

Multiple rescue clauses let you handle different errors in different ways.

Write rescue clauses from specific to general errors.

Use ensure to run code no matter what happens.

Practice

1. What is the purpose of using multiple rescue clauses in Ruby?

easy

A. To repeat the same error handling multiple times

B. To run code only when no errors occur

C. To handle different types of errors with specific responses

D. To skip error handling entirely

Solution

1. Step 1: Understand rescue clauses

   Multiple rescue clauses allow you to catch different error types separately.

2. Step 2: Purpose of specific error handling

   This helps you respond differently depending on the error type.

3. Final Answer:

   To handle different types of errors with specific responses -> Option C

4. Quick Check:

   Multiple rescue clauses = specific error handling [OK]

Hint: Multiple rescue clauses catch different errors separately [OK]

Common Mistakes:

• Thinking rescue clauses run only when no errors occur
• Assuming multiple rescue repeats same handling
• Believing rescue skips error handling

2. Which of the following is the correct syntax for multiple rescue clauses in Ruby?

easy

A. try
# code
rescue ZeroDivisionError
# handle zero division
rescue StandardError
# handle other errors
end

B. begin
# code
catch ZeroDivisionError
# handle zero division
catch StandardError
# handle other errors
end

C. begin
# code
rescue ZeroDivisionError, StandardError
# handle errors
end

D. begin
# code
rescue ZeroDivisionError
# handle zero division
rescue StandardError
# handle other errors
end

Solution

1. Step 1: Identify Ruby error handling syntax

   Ruby uses begin and rescue for error handling, not try or catch.

2. Step 2: Check multiple rescue clauses

   Multiple rescue clauses are written one after another inside begin...end.

3. Final Answer:

   begin # code rescue ZeroDivisionError # handle zero division rescue StandardError # handle other errors end -> Option D

4. Quick Check:

   Ruby uses begin-rescue-end with multiple rescue [OK]

Hint: Use begin-rescue-end blocks for multiple error types [OK]

Common Mistakes:

• Using try or catch instead of rescue
• Combining errors in one rescue without comma
• Incorrect block keywords

3. What will be the output of this Ruby code?

begin
  1 / 0
rescue ZeroDivisionError
  puts 'Zero division error caught'
rescue StandardError
  puts 'Standard error caught'
end

medium

A. Zero division error caught

B. Standard error caught

C. No output, program crashes

D. SyntaxError

Solution

1. Step 1: Identify the error raised

   The code 1 / 0 raises a ZeroDivisionError.

2. Step 2: Match error with rescue clauses

   The first rescue clause catches ZeroDivisionError and prints the message.

3. Final Answer:

   Zero division error caught -> Option A

4. Quick Check:

   ZeroDivisionError triggers first rescue [OK]

Hint: Match error type to first rescue clause that fits [OK]

Common Mistakes:

• Assuming StandardError rescue runs first
• Thinking program crashes without rescue
• Confusing syntax error with runtime error

4. Identify the error in this Ruby code with multiple rescue clauses:

begin
  puts 'Start'
rescue
  puts 'Rescue block'
rescue ZeroDivisionError
  puts 'Zero division error'
end

medium

A. Missing ensure block causes error

B. Multiple rescue clauses after a generic rescue cause syntax error

C. No error, code runs fine

D. Rescue clauses must be inside methods only

Solution

1. Step 1: Check for syntax errors

   In Ruby, a generic rescue clause must come after all specific rescue clauses. Placing a generic rescue before specific ones causes a syntax error.

2. Step 2: Analyze the code

   The code places a generic rescue first, then a specific rescue, which is invalid syntax.

3. Final Answer:

   Multiple rescue clauses after a generic rescue cause syntax error -> Option B

4. Quick Check:

   Generic rescue must be last [OK]

Hint: Generic rescue clause must come after specific rescue clauses [OK]

Common Mistakes:

• Thinking generic rescue before specific causes syntax error
• Believing ensure block is mandatory
• Assuming rescue clauses only work inside methods

5. Given this Ruby code, what will be printed?

def test
  begin
    raise ArgumentError, 'Wrong argument'
  rescue ZeroDivisionError
    puts 'Zero division error'
  rescue ArgumentError
    puts 'Argument error caught'
  ensure
    puts 'Always runs'
  end
end
test

hard

A. Argument error caught
Always runs

B. Zero division error
Always runs

C. Always runs
Argument error caught

D. No output, error not handled

Solution

1. Step 1: Identify raised error

   The code raises ArgumentError with message 'Wrong argument'.

2. Step 2: Match rescue clauses

   The ArgumentError rescue clause runs and prints 'Argument error caught'.

3. Step 3: Understand ensure block

   The ensure block always runs, printing 'Always runs'.

4. Final Answer:

   Argument error caught Always runs -> Option A

5. Quick Check:

   ArgumentError rescued, ensure always runs [OK]

Hint: Ensure block runs after rescue regardless of error [OK]

Common Mistakes:

• Thinking ensure runs before rescue
• Assuming wrong rescue clause runs
• Ignoring ensure block output