Re: [boost] [chrono] Interoperability with ICL and common concepts

Subject: Re: [boost] [chrono] Interoperability with ICL and common concepts
From: Joachim Faulhaber (afojgo_at_[hidden])
Date: 2011-03-16 11:59:42

2011/3/16 Vicente Botet <vicente.botet_at_[hidden]>:
>
> Joachim Faulhaber wrote:
>>
>> 2011/3/16 Howard Hinnant &lt;howard.hinnant_at_[hidden]&gt;:
>>> On Mar 16, 2011, at 8:50 AM, Joachim Faulhaber wrote:
>>>
>>>> 2011/3/15 Howard Hinnant &lt;howard.hinnant_at_[hidden]&gt;:
>>>>> On Mar 15, 2011, at 2:00 PM, Vicente Botet wrote:
>>>>>
>>>>> The current std::chrono::duration default constructor has this
>>>>> definition:
>>>>>
>>>>> constexpr duration() = default;
>>>>
>>>> hmm, I'm a little confused now
>>>>
>>>>> The rationale for this is to give the client and the Rep author as many
>>>>> options as possible:
>>>>>
>>>>> typedef std::chrono::duration D;
>>>>>
>>>>> D d1;  // d1.count() uninitialized - speed
>>>>> D d2 = D();  // d2.count() zero-initialized - safety if you believe 0
>>>>> is safe
>>>>
>>>> This behavior is exactly what I desire
>>>>
>>>>> typedef std::chrono::duration CustomD;
>>>>>
>>>>> CustomD d3;  // d3.count() default constructed
>>>>
>>>> But the current implementation of Boost.Chrono does not work like that:
>>>>
>>>> typedef std::chrono::duration D;
>>>> D d2 = D();  // d2.count() UNINITIALIZED
>>>>
>>>> Will the semantics of
>>>>
>>>>> constexpr duration() = default;
>>>>
>>>> implement the proposed behavior with the new standard?
>>>
>>> Yes.  I'm not sure if any compiler yet implements =default for default
>>> constructors.  I'm hopeful that this feature will be widely implemented
>>> soon.  It has the semantics of defining a compiler-generated default
>>> constructor, which you can only do in C++03 if you don't have any other
>>> constructors declared.
>>
>> That's good to hear, so my wishes for durations default ctor behavior
>> will be fulfilled at least in the future.
>>
>>>>> D d2 = D();  // d2.count() zero-initialized - safety if you believe 0
>>>>> is safe
>>
>
> Howard I have see this behavior with enum classes. It toke me a while to
> understand why the two preceding assignments results in different values,
> but after that it is the same as
>
> int i;
> int j= int();
>
> It is extraneous however :(
>
> Joachim, it seems that you have found a Bug on the emulation of =default
> Boost.Chrono does. Please could you create a ticket.

with pleasure :)

> I think that the user could survive to a duration that is initialized to 0
> even when the user has not requested it.

>From my view (generic interoperability) it's the better choice than
leaving it undefined in both cases.

Best,
Joachim

-- 
Interval Container Library [Boost.Icl]
http://www.joachim-faulhaber.de