Crystal by example: Exceptions

Errors are a fundamental part of software development and are important for diagnosing problems. They should not be avoided, they should be used to solve a problem.

In Crystal, errors can be raised using the raise keyword, which immediately stops the program when the error occurs. They support both messages and classes that inherit from the Exception class.

loop do
  input = gets

  case input
  when nil
    break
  when ""
    puts "Insert somenthing!"
  else
    if input.chomp == "hi"
      raise "Cannot say hi"
    elsif input == "hello"
      raise "Cannot say hello"
    else
      puts "bonjur"
    end
  end
end

$ crystal run exceptions.cr

hi
Unhandled exception: Cannot say hi! (Exception)
  from exceptions.cr:12 in '__crystal_main'