lasitha wrote:
On Tue, Mar 3, 2009 at 5:58 AM, I�aki Baz C. [email protected] wrote:
I would like to just write:
�IPAddr.new(value) rescue ArgumentError puts “Invalid IP”
Unfortunatelly it doesn’t work when the rescue action occurs:
Invalid IP
NoMethodError: undefined method `ArgumentError’ for main:Object
The rescue statement modifier doesn’t take an exception parameter.
You’d have to make do with:
IPAddr.new(value) rescue puts “Invalid IP”
… which rescues StandardError and all subclasses.
However you probably wouldn’t want to do this:
addr = IPAddr.new(value) rescue puts “Invalid IP”
do_something_with(addr)
because the second line would get addr equal to nil, and further errors
would occur. One solution is just to let the ArgumentError propagate
upwards, because the exception message already says “invalid address”:
irb(main):002:0> IPAddr.new(“x”)
ArgumentError: invalid address
Having said that, sometimes I do like to include the offending value in
error messages, so I can end up writing stuff like
begin
addr = IPAddr.new(value)
rescue ArgumentError
raise ArgumentError, “Invalid IP address #{value.inspect}”
end
The risk here is that if the user provides an arbitrarily long string,
you’ll get an arbitrarily long exception message too.
Another option is to stick rescue clause(s) at the end of a method body,
because you don’t need a ‘begin’.
def foo(value)
addr = IPAddr.new(value)
do_something_with(addr)
rescue ArgumentError
puts “Invalid IP address”
raise # or not, it’s up to you
end
On the plus side, this prevents the nil addr being used. On the minus
side, any ArgumentError in the body of foo or any of the methods it
calls will be reported as “Invalid IP address”
Regards,
Brian.