From: Ara.T.Howard@...
Date: 2005-05-14T06:35:29+09:00
Subject: Re: Customing the Exception class

On Sat, 14 May 2005, Daniel Berger wrote:

> Hi all,
>
> I have a program where I want to send all errors to a file.  So, I did this:
>
> class Exception
>    alias :old_init :initialize
>    def initialize(arg)
>       old_init(arg)
>       File.open("log.txt","a+"){ |fh| fh.puts("Error: #{arg}") }
>    end
> end
>
> This works for most errors, but it doesn't seem to work when the error
> is a SystemCallError.
>
> For example, this writes to the log as expected:
>
> print "Some crazy division: "
> p 1/0
>
> But this does not:
>
> File.open("non-existant file")
>
> The latter raises an Errno::ENOENT.
>
> Why, if SystemCallError is a subclass of Exception, does my approach not
> work?  How do I make this work as expected?

maybe new?


   harp:~ > cat a.rb
   class Exception
     class << self
       alias ____new new
       def new(*a, &b)
         ret = ____new(*a, &b)
         STDERR.puts "new: <#{ a.inspect }>"
         ret
       end
     end
     alias ____init initialize
     def initialize(*a, &b)
       ret = ____init(*a, &b)
       STDERR.puts "initialize: <#{ a.inspect }>"
       ret
     end
   end

   SystemCallError::new 42

   harp:~ > ruby a.rb
   new: <[42]>

not sure why...

-a
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