CodeToLive

Error Handling in Ruby

Ruby uses exceptions for error handling, which can be caught using begin, rescue, and ensure blocks.

Basic Error Handling

Use begin and rescue to handle exceptions. 


begin
  result = 10 / 0
rescue ZeroDivisionError => e
  puts "Error: #{e.message}"
end

Multiple Rescue Clauses

You can handle multiple types of exceptions by adding multiple rescue clauses. 


begin
  # Code that may raise an exception
  file = File.open("nonexistent_file.txt")
  content = file.read
rescue Errno::ENOENT => e
  puts "File not found: #{e.message}"
rescue StandardError => e
  puts "An error occurred: #{e.message}"
end

Retrying Code

Use retry to re-execute the begin block after an exception is rescued. 


attempts = 0
begin
  attempts += 1
  puts "Attempt #{attempts}"
  raise "An error occurred"
rescue => e
  retry if attempts < 3
  puts "Failed after #{attempts} attempts"
end

Raising Exceptions

You can raise exceptions explicitly using the raise keyword. 


def divide(a, b)
  raise ArgumentError, "Divisor cannot be zero" if b == 0
  a / b
end

begin
  result = divide(10, 0)
rescue ArgumentError => e
  puts "Error: #{e.message}"
end

Custom Exceptions

You can define custom exceptions by subclassing StandardError. 


class CustomError < StandardError
end

begin
  raise CustomError, "Something went wrong!"
rescue CustomError => e
  puts "Caught custom error: #{e.message}"
end

Ensure Block

The ensure block is used to execute code regardless of whether an exception was raised. 


begin
  file = File.open("example.txt")
  content = file.read
rescue => e
  puts "Error: #{e.message}"
ensure
  file.close if file
end

Best Practices

Next: Concurrency in Ruby