From: Tomas Matousek <Tomas.Matousek@...>
Date: 2009-03-06T16:52:47+09:00
Subject: [ruby-core:22698] Re: [Bug #1248] e.exception(e) returns self

Well the reason is that arg is supposed to be a message, right? A message can be an arbitrary object. So if I pass e as a message, why it doesn't become a value of the message property?

irb(main):001:0> a = Exception.new
=> #<Exception: Exception>
irb(main):002:0> b = Exception.new
=> #<Exception: Exception>
irb(main):003:0> c = a.exception(b)
=> #<Exception: #<Exception:0x31f1d34>>              # this is ok, b is now a message of c
irb(main):004:0> c.message == b 
=> true
irb(main):005:0> c = a.exception(a)
=> #<Exception: Exception>
irb(main):006:0> c.message == a                      # a is not a message of c
=> false
irb(main):007:0> c == a                              # instead, c is a
=> true

It's not about saving an allocation. It's that for all objects, except for self, the method sets a message on a new exception object. Only for self it doesn't. (at least as far as I observe)

Tomas

-----Original Message-----
From: Yukihiro Matsumoto [mailto:matz@ruby-lang.org] 
Sent: Thursday, March 05, 2009 10:55 PM
To: ruby-core@ruby-lang.org
Subject: [ruby-core:22696] Re: [Bug #1248] e.exception(e) returns self

Hi,

In message "Re: [ruby-core:22687] [Bug #1248] e.exception(e) returns self"
    on Fri, 6 Mar 2009 04:36:56 +0900, Tomas Matousek <redmine@ruby-lang.org> writes:

|Exception#exception(arg) instance method should return a new exception of the same class as self with message arg. It does so for any object passed in as an argument except for if e is passed in. I don't see any reason for special casing the method this way.
|
|Repro:
|e = Exception.new
|p e.exception(e).object_id == e.object_id  # => true; it should return false

You've missed the reason why you considered this behavior to be a bug.
Have you been bitten by this?  Or just for the sake of your feeling of
consistency?  Avoiding object allocation is one good reason.

							matz.