[boost] Re: [optional] new assignmet semantic and references

From: David Abrahams (dave_at_[hidden])
Date: 2005-03-05 14:20:44

Joel de Guzman <joel_at_[hidden]> writes:

> David Abrahams wrote:
>> "Brock Peabody" <brock.peabody_at_[hidden]> writes:
>> 
>>>it improves my ability to make code self-documenting.
>>> Personally, I like it the way it is.  I've used optional quite a
>>> bit and it
>>>makes sense to me that operator= changes what an optional holds.  I don't
>>>think it is a good idea to give operator= special semantics for references.
>> I had the same feeling.  That's what I meant when I said
>>   "It depends on whether you view optional<T> as a T that might just
>>   happen to be missing, or as a container for a T."
>> I think "a container for a T" is a more manageable meaning for
>> optional<T>.
>
> FWIW, a tuple<T&> can't be re-bound.

Correct.  It's all a question of what we want optional to be.

> I'll state my point again. I noticed this odd behavior of
> optional some years ago: giving optional re-binding semantics
> *is actually* giving it special semantics and requires special
> case handling. This leads to subtle problems like the one
> Fernando is experiencing now. If you want rebinding semantics,
> use a pointer, or use boost::ref. The right behavior, I strongly
> believe, is to do as the references do. This is what tuple did
> and we have nary a problem with it.

Okay.

-- 
Dave Abrahams
Boost Consulting
www.boost-consulting.com