[PATCH] PR libstdc++/79162 ambiguity in string assignment due to string_view overload (LWG 2946)

[Daniel Krügler]

2017-07-28 22:29 GMT+02:00 Daniel Krügler <daniel.kruegler@gmail.com>:
> 2017-07-28 22:25 GMT+02:00 Tim Song <t.canens.cpp@gmail.com>:
>> On Fri, Jul 28, 2017 at 4:10 PM, Daniel Krügler
>> <daniel.kruegler@gmail.com> wrote:
>>> +      // Performs an implicit conversion from _Tp to __sv_type.
>>> +      template<typename _Tp>
>>> +        static __sv_type _S_to_string_view(const _Tp& __svt)
>>> +        {
>>> +          return __svt;
>>> +        }
>>
>> I might have gone for
>>
>> +        static __sv_type _S_to_string_view(__sv_type __svt) noexcept
>> +        {
>> +          return __svt;
>> +        }
>>
>> With that, we can also use noexcept(_S_to_string_view(__t)) to make up
>> for the absence of is_nothrow_convertible (basically the same thing I
>> did in LWG 2993's PR).
>
> Agreed, that makes very much sense. I will adjust the P/R, but before
> I resubmit I would like to get feedback whether the other two compare
> functions also should become conditionally noexcept.

Locally I have now performed the sole change of the _S_to_string_view
declaration getting rid of the template, but would also like to gather
feedback from the maintainers whether I should also change the form of
the conditional noexcept to use the expression

noexcept(_S_to_string_view(__t))

instead of the current

is_same<_Tp, __sv_type>::value

as suggested by Tim Song.

I'm asking also, because I have a paper proposing to standardize
is_nothrow_convertible submitted for the upcoming C++ mailing - This
would be one of the first applications in the library ;-)

> Thanks,
>
> - Daniel