Exceptions

Rescue a failure

Wrap risky code in begin/rescue.

begin
  Integer("abc")
rescue ArgumentError => e
  puts "Could not parse: #{e.message}"
end

Raise your own

Raise when a method receives invalid input.

def find(id)
  raise ArgumentError, "id must be positive" if id <= 0
  "ok"
end

Ensure cleanup

ensure runs whether or not an error occurred.

begin
  puts "work"
ensure
  puts "cleanup"
end

Exception tips

• Rescue specific classes when possible
• Do not rescue StandardError silently everywhere
• Use exceptions for exceptional cases, not normal branching
• Let unexpected bugs surface during learning