From: ES <ruby-ml@...>
Date: 2005-10-07T06:50:11+09:00
Subject: Re: Customizing Exception, but only when an error is raised

Robert Klemme wrote:
> Daniel Berger <Daniel.Berger@qwest.com> wrote:
> 
>> Hi all,
>>
>> Say I do something like this do the Exception class:
>>
>> class Exception
>>    alias :old_init :initialize
>>    def initialize(*args)
>>       old_init(*args)
>>       do_stuff
>>    end
>>
>>    def do_stuff
>>       puts "Hello World!"
>>    end
>> end
>>
>> And, I want +do_stuff+ to fire off if an error is *raised* but not if
>> it is caught (and not re-raised).  In other words, I would expect
>> +do_stuff+ to fire off in this example:
>>
>> begin
>>    0/0
>> rescue ZeroDivisionError
>>    raise
>> end
>>
>> But I don't want to fire off in this example:
>>
>> begin
>>    0/0
>> rescue ZeroDivisionError
>>    # Do nothing
>> end
> 
> 
> The moment an exception is thrown an exception istance is created.  So 
> your code will be invoked on every raise.  No way to prevent that if you 
> put it into the constructor.

Just 'raise' by itself seems to raise the same exception object (it
does not even #dup it I think) so the #initialize would only work
whenever an Exception is raised the first time.

>> Is there a way I can accomplish this?
> 
> 
> Write a custom method that does the raising.
> 
> def my_raise(cl,*a)
>  ex = cl.new(*a)
>  ex.do_stuff
>  raise ex
> end
> 
> Kind regards
> 
>    robert

E