Re: [boost] [gsoc16] Can I quickly check if the below really is the best approach?

Subject: Re: [boost] [gsoc16] Can I quickly check if the below really is the best approach?
From: Nevin Liber (nevin_at_[hidden])
Date: 2016-01-14 12:59:35

On 14 January 2016 at 11:54, Agustín K-ballo Bergé <kaballo86_at_[hidden]>
wrote:

> On 1/14/2016 2:45 PM, Gottlob Frege wrote:
>
>> On Wed, Jan 13, 2016 at 1:56 PM, Nevin Liber <nevin_at_[hidden]>
>> wrote:
>>
>>> On 13 January 2016 at 12:25, Lee Clagett <forum_at_[hidden]> wrote:
>>>
>>> The macro `STRING_VIEW` seems unnecessary because the `string_view`
>>>> constructor taking a single NULL-terminated string is also
>>>> `constexpr`.
>>>>
>>>>
>>> While the templated constructor for basic_string_view is constexpr, this
>>> constructor for string_view cannot be used in a constexpr context because
>>> char_traits<char>::length isn't constexpr. :-(  See LWG 2232
>>> <http://cplusplus.github.io/LWG/lwg-active.html#2232>.
>>>
>>> I've been told it works this way by design...
>>>
>>> So yes, we do need the macro.
>>>
>>
>> Can it be a constexpr function that returns an initializer list?
>>
>
> No, because initializer lists are backed by arrays of automatic storage,
> so the returned `initializer_list` would immediately dangle.
>
> Or
>> something, anything,... I hate macros :-(
>>
>
> Yes, templates, as usual:
>
>     template <typename CharT, std::size_t N>
>     constexpr std::experimental::basic_string_view<CharT>
>     make_string_view(CharT const (&str)[N]) noexcept {
>       return {str, N - 1};
>     }
>
>     constexpr string_view sv = make_string_view("hello");
>     static_assert(sv.size() == 5);
>

That does not do the same thing if the literal has embedded '\0' characters
or if you pass it an array that isn't a '\0'-terminated string.
-- 
 Nevin ":-)" Liber  <mailto:nevin_at_[hidden]>  [phone]