Re: [boost] [date-time][threads] Integrating C++0x clocks, time points, and durations into Boost?

From: Darren Garvey (darren.garvey_at_[hidden])
Date: 2008-06-18 23:50:47

Oops, here's the attachments. (I think it's bed time)

2008/6/19 Darren Garvey <darren.garvey_at_[hidden]>:

> 2008/6/18 Beman Dawes <bdawes_at_[hidden]>:
>
>> Beman Dawes wrote:
>>
>>> A slightly updated version of
>>> http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2615.html was
>>> accepted at the C++ committee meeting last week.
>>
>>
>>> <snip>
>>
>>
>>> I've emailed Howard to see if his prototype implementation can be made
>> available with the Boost license. The answer was yes, but he points out that
>> an independent implementation would be better in terms of flushing out
>> issues with the proposed text for the standard.
>>
>> The proposal has several components:
>>
>> <snip>
>
>
>> * ratio: "ratio is a general purpose utility inspired by Walter Brown
>> allowing one to easily and safely compute rational values at compile time."
>> The proposal puts this in the Utilities chapter of the standard library. It
>> has a lot of similarity to type traits.
>>
>
> I thought this bit looked simple enough to have a go at, so I took a shot
> at it and am attaching the results (tested with gcc 4.2.3 on Ubuntu). My
> conclusion is that the (relevant bit of) text is as clear as it needs to be
> - since I could follow it - except for one point:
>
> When it says:
> """
> num shall have the value sign(N)*sign(D)*abs(N)/gcd.
>
> den shall have the value abs(D)/gcd.
>
> """
>
> ... are sign() and abs() supposed to be runtime functions? I implemented
> them as meta-functions - I'm sure these are in boost somewhere, I just don't
> know where. Maybe compilers are generally clever enough, or the standard
> guarantees those functions will be evaluated at compile time? I'm never sure
> where the line is drawn on this one...
>
> The attached code is quite straightforward and basically does what the text
> says it should (I hope), but no more. The main limitation is that it uses
> static_gcd<> from Boost.Math. That meta-function is parametrised with
> `unsigned long` instead of `intmax_t` which limits how big the allowed
> numbers can be. I tried without luck to change the relevant header but I
> suppose it's not really relevant to this experiment.
>
> One other thing that threw me:
>
> """
>
> The proposal is entirely an add-on. It will break no existing C++03 code,
> subject to the usual caveat that user code giving a using namespace stdmay see name clashes. Even that possibility is mitigated because the time
> portion of the proposal is in a std sub-namespace.
>
> """
>
> I had no idea that it was a given that `using namespace std` could cause
> name clashes... Oh well, good thing I don't do that. :)
>
> Anyway, I hope Boost gets a high-resolution timer quick-sharp; it's long
> overdue imho.
>
>
> Kind regards,
>
> Darren
>