2017-11-13 21:23 GMT+01:00 François Dumont <[email protected]>:
> On 10/11/2017 21:57, Jonathan Wakely wrote:
>>> diff --git a/libstdc++-v3/include/bits/streambuf_iterator.h
>>> b/libstdc++-v3/include/bits/streambuf_iterator.h
>>> index 0a6c7f9..b60626a 100644
>>> --- a/libstdc++-v3/include/bits/streambuf_iterator.h
>>> +++ b/libstdc++-v3/include/bits/streambuf_iterator.h
>>> @@ -417,6 +421,55 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>> return __last;
>>> }
>>>
>>> + template<typename _CharT, typename _Distance>
>>> + inline _GLIBCXX17_CONSTEXPR void
>>
>>
>> This function can never be constexpr.
>
> I just replicate the _GLIBCXX17_CONSTEXPR qualification of the general
> std::advance overload. I am not clear about those different constexpr
> concepts but I also found strange that it could be consider as such.
The general std::advance function can be constexpr, depending on the
actual iterator, e.g.
#include <iterator>
template<class T>
constexpr T* next(T* p)
{
std::advance(p, 1);
return p;
}
int main()
{
static int arr[2] = {1, 2};
constexpr int* p = next(arr);
}
but as Jonathan already said, for std::istreambuf_iterator<T> this can
never be true (because of the involved IO operations).
- Daniel
