Matt Pulver wrote:
For example, the following will not compile with pre-17 compilers if `constexpr` is dropped:
template<typename RealType,size_t Order> constexpr size_t dimension<RealType,Order>::depth() { if constexpr (is_dimension<RealType>::value) return 1 + RealType::depth(); else return 1; }
This specific case isn't hard to support either, although whether you would want to invest the effort is up to you. template<typename RealType,size_t Order> constexpr size_t dimension<RealType,Order>::depth() { return dimension<RealType,Order>::depth_impl( is_dimension<RealType>() ); } template<typename RealType,size_t Order> constexpr size_t dimension<RealType,Order>::depth_impl( true_type ) { return 1 + RealType::depth(); } template<typename RealType,size_t Order> constexpr size_t dimension<RealType,Order>::depth_impl( false_type ) { return 1; }