Constexpr if alternative

Question

I would like to use constexpr if to branch at compile time, but it does not seem to be supported by the latest MSVC compiler. Is there an alternative to the following?:

template<typename T> void MyFunc() {     if constexpr(MeetsConditions<T>::value)     {         FunctionA<T>();     }     else     {         FunctionB<T>();     } } 

In short: Can I simulate constexpr if when it is not supported by the compiler?

Answer 1

One of pre-C++17 ways is to use partial template specializations, like here:

template <typename T, bool AorB> struct dummy;  template <typename T, true> struct dummy {     static void MyFunc() {  FunctionA<T>(); } }  template <typename T, false> struct dummy {     static void MyFunc() {  FunctionB<T>(); } }  template <typename T> void Facade() {     dummy<T, MeetsConditions<T>::value>::MyFunc(); } 

If you need more, than 2 specializations - you can use enum or integral value, and make specializations for all needed enums.

Another way is to use std::enable_if:

template <typename T> std::enable_if<MeetsConditions<T>::value, void>::type MyFunc() {    FunctionA<T>(); }  template <typename T> std::enable_if<!MeetsConditions<T>::value, void>::type MyFunc() {    FunctionB<T>(); } 

Answer 2

You can do it the old fashioned, tried and tested tag dispatch way:

template<typename T> void MyFuncImpl(std::true_type) {   FunctionA<T>(); }  template<typename T> void MyFuncImpl(std::false_type) {   FunctionB<T>(); }  template<typename T> void MyFunc() {   MyFuncImpl<T>(std::integral_constant<bool, MeetsConditions<T>::value>{}); }