Re: [boost] [variant] Please vote for behavior

Subject: Re: [boost] [variant] Please vote for behavior
From: Paul Smith (pl.smith.mail_at_[hidden])
Date: 2013-02-01 10:20:38

On Fri, Feb 1, 2013 at 4:57 PM, Dave Abrahams <dave_at_[hidden]> wrote:
>
> on Thu Jan 31 2013, Paul Smith <pl.smith.mail-AT-gmail.com> wrote:
>
>> On Thu, Jan 31, 2013 at 10:11 PM, Dave Abrahams <dave_at_[hidden]> wrote:
>>>
>>> on Thu Jan 31 2013, Paul Smith <pl.smith.mail-AT-gmail.com> wrote:
>>>
>>>> On Thu, Jan 31, 2013 at 3:22 AM, Dave Abrahams <dave_at_[hidden]> wrote:
>>>>>
>>
>>>>> on Mon Jan 28 2013, Paul Smith <pl.smith.mail-AT-gmail.com> wrote:
>>>>>
>>>>>> This issue has been discussed more than once before, and nothing I say
>>>>>> here is my own opinion, so please don't take it out on me.
>>>>
>>>>>> For example, see N3264 (CH-18 and US-85: Clarifying the state of
>>>>>> moved-from objects (Revision 1)):
>>>>>>
>>>>>> http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2011/n3264.htm
>>>>>>
>>>>>>> and Dave confirms that,
>>>>>>
>>>>>> I don't want to read into what Dave said too much, because he's here
>>>>>> and he can clarify it. But I believe what he said is that specific
>>>>>> algorithms, in their own localized context, practically only require
>>>>>> destructibility and assignability. And even then,
>>>
>>> I was disavowing this part because I don't claim to know it for sure:
>>>
>>>>>> it's not something the standard actually guarantees in general,
>>>>>> though, and the requirements are still much stricter, perhaps
>>>>>> superfluously so.
>>>
>>> and I was disavowing this part because I disagree with it:
>>>
>>>>>> it's a good selling point for having destructive move semantics -
>>>>>
>>>>> That doesn't sound like anything I meant to say, but I do agree fully
>>>>> with the resolutions (if not the NB comments) in the paper cited above.
>>>>
>>>> Then what did you mean?
>>>
>>> See above.
>>
>> Actually, that's not really what I asked. Joel asked you if
>> destructibility and assignability is all the standard library needs
>> from moved-from objects. You responded: "That's all the standard
>> library will use."
>
> Yes.
>
>> Now you seem to say the opposite.
>
> Where?
>
>> I think this was a source of confusion :-)
>
> I can imagine it would be.

Okay, I'm truely confused about what you're saying then.

Either the standard library requires moved-from user-types to keep
meeting all their requirements, or it only requires them to remain
destructible and assignable. The standard says the former. The wording
that appears in the standard is the same (or almost the same) wording
as the resolution of N3264, which is what you say you fought for.

The only other way I can interpret "That's (destructibility and
assignability) all that srandard library will use" is "that's all it
will use in practice", but you say you disavow that.

So, please, could you rephrase this sentence in a more elaborate way?

--
Paul Smith