c++ - Template error C2244 unable to match function definition to an existing declaration using constexpr in Microsoft Visual Studio 2015 -

i'm getting : error c2244 unable match function definition existing declaration while using constexpr.

template<int n> constexpr int x() {     return n*n; }  template<int x, int n> class b { public:     int data; };  template<int n> class { public:     int f(b<x<n>(), n> b); };  template<int n> int a<n>::f(b<x<n>(), n> b) {     return b.data; }  int main() {     a<10> a;     return 0; } 

if remove constexpr function , replace expression n*n, works fine.

gnu c++ compiles , expect, according https://msdn.microsoft.com/en-us/library/hh567368.aspx, constexpr works correctly on visual studio 2015.