C++17 changes N4268 Allowing more non-type template args

Question

I have VS2019 ver16.11.40 (updated VS).

I have sample C++ code accroding to C++17 changes Allowing more non-type template args:

#include <iostream>
 
template<double Value>
constexpr double getFactorial()
{
    return Value * getFactorial<Value - 1.0>();
}
 
template<>
constexpr double getFactorial<0.0>() { return 1.0; }
 
int main()
{
    std::cout << getFactorial<4.0>() << '\n';
}

This code doesn't want to compile on mine VS2019 ver.16.11.40 despite document:

link

says this C++17 change applied to VS 2017 15.5, see screenshot below:

What the matter? Why this C++17 code doesnt want compiles on my VS2019 v.16.11.40?

Answer 1

It seems that double was not yet supported, but it is possible to use long or long long:

template<long Value>
constexpr long getFactorial( )
{
    return Value * getFactorial<Value - 1>( );
}

template<>
constexpr long getFactorial<0>( ) { return 1; }

To use double, consider C++20 and Visual Studio 2022 (https://en.cppreference.com/w/cpp/language/template_parameters).

Answer 2

Thank you very much for answer. I read this document C++17:

https://en.cppreference.com/w/cpp/compiler_support/17

Code from example describes C++17 changes, but code same doesnt not compiled on my VS2019 ver16.11.40.

#include <iostream>
template<int* p> class X { };

int a[10];

struct S { int m; static int s; } s;

int main()
{
    X<&a[2]> x3; // before C++17 error: address of array element
    X<&s.m> x4;  // before C++17 error: address of non-static member
}