SFINAE constexpr error in Microsoft Visual C++ - c++

Question

Simple SFINAE code using constexpr fails to compile. The same code compiles in g++.
This issue comes only when constexpr is used. While using std::is_integral_v<T>, it compiles.
// test code
#include<iostream>
template<typename T>
constexpr inline bool is_integral() {
return std::is_integral_v<T>;
}
template<typename T>
constexpr inline bool is_floating_point() {
return std::is_floating_point_v<T>;
}
struct tester {
template<typename T>
std::enable_if_t<is_integral<T>(), void> operator()(int* p){
//integral version
std::cout<<"integral\n";
}
template<typename T>
std::enable_if_t<is_floating_point<T>(), void> operator()(int* p){
//floating point version
std::cout<<"floating\n";
}
template <typename T, typename... Args>
std::enable_if_t<!is_integral<T>() && !is_floating_point<T>(), void> operator()(Args&&...)
{
std::cerr<<"not supported.\n";
}
};
enum class type { INT, FLOAT, STRING};
void type_dispatcher(type tp) {
tester t;
switch(tp) {
case type::INT:
t.operator()<int>(nullptr);
break;
case type::FLOAT:
t.operator()<float>(nullptr);
break;
default:
std::cout<<"Unsupported\n";
}
}
int main() {
type t1{type::INT}, t2{type::FLOAT}, t3{type::STRING};
type_dispatcher(t1);
type_dispatcher(t2);
type_dispatcher(t3);
return 0;
}
Error: cl.exe /std:c++17 ..\sfinae_test.cpp
Microsoft (R) C/C++ Optimizing Compiler Version 19.29.30136 for x64
Copyright (C) Microsoft Corporation. All rights reserved.
sfinae_test.cpp
..\sfinae_test.cpp(21): error C2535: 'enable_if<0,void>::type tester::operator ()(int *)': member function already defined or declared
..\sfinae_test.cpp(16): note: see declaration of 'tester::operator ()'
..\sfinae_test.cpp(44): error C2672: 'tester::operator ()': no matching overloaded function found
..\sfinae_test.cpp(44): error C2893: Failed to specialize function template 'enable_if<0,void>::type tester::operator ()(int *)'
..\sfinae_test.cpp(16): note: see declaration of 'tester::operator ()'
..\sfinae_test.cpp(44): note: With the following template arguments:
..\sfinae_test.cpp(44): note: 'T=float'
Folding all the code into if constexpr works.
Related issue: https://developercommunity.visualstudio.com/t/constexpr-function-in-sfinae/1048586
Is there any solution/hack to this problem?

Answer 1

You can use enable_if as template parameter, like this.