Check static_assert in unit test

Question

I would like to make sure that static_assert works as it should in unit test. That is, if I have

class MyClass {static_assert(my_type_trait<T>::value, "error"); };

then in the unit test MyClass<TypeWithTrait> myClass;should “pass” and MyClass<TypeWithoutTrait> myClass;should “fail”.

Is it possible to do something like this?

Answer 1

If you want to verify that something cannot be compiled, you will need to check the external code. Just write a simple file, for example:

#include "MyClass.h"

int main() { 
    MyClass<%T%> m;
}

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Answer 2

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template <class T>
using void_t = void;

template <class T>
struct foo;

template <>
struct foo <double> {};

template <class T, class = void>
struct has_foo_trait : std::false_type {};

template <class T>
struct has_foo_trait<T, void_t<decltype(foo<T>{})>> : std::true_type {};

int main(int, char**) {
  std::cerr << has_foo_trait<int>::value;
  std::cerr << has_foo_trait<double>::value;
  return 0;
}

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