Message-oriented (duck-typed) exceptions

I thought somebody would implement the message-oriented exception mechanism I hinted at, but nobody did so here's the obvious implementation (4 minutes wall clock time):

Usage

def foo
  #...
  raise EX[:critical, :alert_user] # if ...
  # ...
end

def bar
  begin
    foo
  rescue EX[:critical]
    puts "Releasing resources"
    raise
  end
end

begin
  bar
rescue EX[:alert_user] => e
  puts "=" * 80
  puts "Bad news:"
  puts e.backtrace
  puts "=" * 80
end
# >> Releasing resources
# >> ================================================================================
# >> Bad news:
# >> -:30:in `foo'
# >> -:36:in `bar'
# >> -:44
# >> ================================================================================

Implementation

Using respond_to? to remain close to the message-oriented nature of huh everything else:

def MOException(data, *methods) # message-oriented exceptions
  Class.new(Exception) do
    class <<self; self end.class_eval do
      define_method(:===){|ex| methods.any?{|m| ex.respond_to?(m)}}
    end
    methods.each{|m| define_method(m){ }} 
    # something of interest could be done in them? maybe some sort of
    # negotiation between the exception and the ex. handler...
    define_method(:data){ data }
  end
end

EX = Class.new{ def [](*meths); MOException(nil, *meths) end }.new

That's great - Brian Mitchell (2007-03-23 (Fri) 12:17:59)

That's great, though I wonder if some exceptions I tend to use, have such boring interfaces that it makes it hard to use this outside of my own library code. Maybe this is a sign that we need our exceptions to be more interesting. This has been quite thought provoking for me. I'll keep this in mind next time I build up some exceptions and see if I can't break out of this type of one-line lazyness:

   class DumbException < RuntimeException; end

Thanks for the great content you share here, Brian.

mfp 2007-03-24 (Sat) 17:39:33

Yes, it also seems to me that maybe exceptions could be more intelligent, carry more information about what went wrong and somehow collaborate with the exception handler. Just a gut feeling.

Thanks for your encouragement.