From: Gennady Bystritsky <Gennady.Bystritsky@...>
Date: 2010-03-25T00:37:49+09:00
Subject: Re: what's the suggested raise Exception idiom?


On Mar 24, 2010, at 1:31 AM, Robert Klemme wrote:

> 2010/3/24 Gennady Bystritsky <Gennady.Bystritsky@quest.com>:
>> 
>> On Mar 23, 2010, at 2:45 PM, Robert Klemme wrote:
> 
>>> I believe raise a,b,c,d... is merely syntactig sugar for raise
>>> a.new(b,c,d...) with a bit of added functionality (e.g. if a is not an
>>> exception class there is an error, if a is a String a StandardError is
>>> raised).
>> 
>> Not exactly so. According to the passage from RI below, "raise" with an exception class as a first paremeter accepts up to 2 additional parameters -- the first one will be used as an argument to new when the exception object is instantiated, and the second, if any, must be an array representing callback information.
> 
> Right you are.  Thanks for the education!  Apparently I never had the
> need for this. :-)
> 
>> When I need an exception class with more than one argument, I use something like the following:
>> 
>> class DimensionError < RuntimeError
>>  attr_reader :width, :hight
>>  def initialize(*args)
>>    @width, @hight = *args
>>    super "Wrong dimension #{width}x#{hight}"
>>  end
>> end
>> 
>> begin
>>  raise DimensionError, [ 5, 3 ]
>> rescue DimensionError => error
>>  error.wigth
>>  error.length
>> end
> 
> That does not seem to work as you expect on 1.9:
> 
> irb(main):038:0> class E1 < Exception
> irb(main):039:1> def initialize(*a) p a end
> irb(main):040:1> end
> => nil
> irb(main):041:0> begin; raise E1,[1,2]; rescue Exception => e; p e; end
> [[1, 2]]
> #<E1: E1>
> => #<E1: E1>
> irb(main):042:0> class E1 < Exception
> irb(main):043:1> def initialize(*a) x,y=*a; p x,y end
> irb(main):044:1> end
> => nil
> irb(main):045:0> begin; raise E1,[1,2]; rescue Exception => e; p e; end
> [1, 2]
> nil
> #<E1: E1>
> => #<E1: E1>
> irb(main):046:0> RUBY_VERSION
> => "1.9.1"
> 
> You would have to do
> 
> irb(main):047:0> class E1 < Exception
> irb(main):048:1> def initialize(a) x,y=*a; p x,y end
> irb(main):049:1> end
> => nil
> irb(main):050:0> begin; raise E1,[1,2]; rescue Exception => e; p e; end
> 1
> 2
> #<E1: E1>
> => #<E1: E1>
> irb(main):051:0>
> 
> Note the missing splash operator in initialize's argument list.

Well, I am still on 1.8.6, missed the issue on 1.9.x ;-). Thanks for pointing this out. Besides, an exception's initialize() accepts only one parameter anyway, so your no-splash version should work for 1.8.x as well. I started using Hash-based initialize() recently, and it seems to work same way both in 1.8 and 1.9.

Gennady.