Question

In ruby, I’m not quite sure how to handle whether objects are nil or not.

For example I have the following:

begin
    sp = SerialPort.new(@serial_device, @serial_bps, @serial_par, @serial_bits, SerialPort::NONE)
    tcp = TCPSocket.new(@host, @port)

    if (sp)
        sp.print(command)
        sp.close
    elsif
        tcp.print(command)
        tcp.close
    end

    say siri_output
rescue
    pp $!
    puts "Sorry, I encountered an error: #{$!}"
ensure
    request_completed 
end

The problem is that the first object returns an error relating to:

No route to host - connect(2)

Which is correct, because TCP isn’t connected duh. So I’d like it to use the next object instead.

Is there a way to do this without using certain Exceptions, I was wondering if there’s a better way of doing what I’m after any how.

Answer 1

The problem is not the checks, you are doing that right. Anything that’s not nil or false is true in ruby. It’s that when you get an exception on the row that starts with “sp = ..” the execution jumps to the resque block. You should restructure the code like this (I’ve removed the ensure clause because I do not know what it does). A good thing to do it’s to rescue every specific type of exception in it’s own row. by class name ex. NoConnectivityException => e (or what the class of the exception would be).

 begin
     sp = SerialPort.new(@serial_device, @serial_bps, @serial_par, @serial_bits, SerialPort::NONE)
     sp.print(command)
     sp.close
     say siri_output
 rescue Exception => e
     puts "Sorry, I encountered an error: #{e.inspect}"
     puts "trying TCP"
     begin
         tcp = TCPSocket.new(@host, @port)
         tcp.print(command)
         tcp.close
         say siri_output
     rescue Exception => e
         puts "Sorry, I encountered an error: #{e.inspect}"
     end
 end

For quick and sloppy programming you can do another thing, but it’s not recommended and generally a pain to debug, as any error results in nil and is silenced.

sp = SerialPort.new(@serial_device, @serial_bps, @serial_par, @serial_bits, SerialPort::NONE) rescue nil
tcp = TCPSocket.new(@host, @port) rescue nil

This way you’d end up with either a SerialPort object or nil object in the sp variable, and the same for sp.