From: Joe Van Dyk <joevandyk@...>
Date: 2005-08-31T03:00:31+09:00
Subject: Re: custom exceptions

On 8/30/05, Joe Van Dyk <joevandyk@gmail.com> wrote:
> Hi,
> 
> When should you define your own exceptions?  Any rules of thumb?
> 
> I'm writing an application that runs on a computer and listens for
> requests to start, kill, and view log files for other applications on
> that computer.  Say I get a request to start an application on that
> computer and the requested executable doesn't exist.  Should I throw a
> custom exception then?  Or, say an application dies unexpectedly.
> What should I use for an exception then?

The start function follows:

class Application
...
  def start
    raise "No executable given!" if not @executable
    if @pid = fork
      Process.detach @pid
      @status = :running
    else
      @options.each do |option_name, option_value|
        ENV[option_name] = option_value
      end
      args = @arguments.join " " 
      exec "#{ basedir }/#{ version }/#{ executable } #{ args }"
    end
  end
...
end

So, if there's no valid executable, then the exec call will fail. 
What's the best way of transmitting that information to the rest of
the system?