Re: constexpr memeber function not constexpt anymore in v10

[Klaus Doldinger <klaus.doldinger64@xxxxxxxxx>]

Am 19.02.20 um 11:02 schrieb Jonathan Wakely:
> On Wed, 19 Feb 2020 at 07:53, Klaus Doldinger
> <klaus.doldinger64@xxxxxxxxx> wrote:
>>
>> The following was possible in v9:
>>
>> template<auto N>
>> struct A {
>>     constexpr auto size() const {
>>         return N;
>>     }
>> };
>>
>> template<typename A>
>> void foo(const A& a) {
>>     constexpr auto s = a.size();
>> }
>>
>> int main() {
>>     A<10> x1;
>>     foo(x1);
>> }
>>
>> In v10 this is rejected.
>>
>> Looks like a bug?
> 
> No, I don't think so. The parameter a is not a constant expression, so
> a.size() is not a constant expression, so can't be used to initialize
> a constexpr variable.
> 

That would be weird.
If so, the follwing would be impossible:

    std::array<int, 10> a;
    std::array<int, a.size()> b;