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

Subject: Re: [boost] [variant] Please vote for behavior
From: Larry Evans (cppljevans_at_[hidden])
Date: 2013-02-01 11:06:28

On 02/01/13 09:20, Paul Smith wrote:
> 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.
[snip]
Could you please give a link to the post where Dave disavows that and
give a quote of the sentence where that's made?  It would save other
readers a good bit of time searching for this since this has been
a *long* thread.

TIA.

-regards,
Larry