Pfthb

I want to unit test equivalent templated member function of a class template. (As a background, I want to offer the users of the library "classical" function notation with .bar() and a tacit notation with |, &, etc. But I do not want to duplicate the complete test code.)

#include <utility> 

template <typename T>
struct foo
(U&& u)&& 
 return bar(std::forward<U>(u));
 

 template <typename U>
 auto bar(U&& u) const& 
 // whatever happens here.
 return foo<T>();
 

 template <typename U>
 auto operator;

int main() 
 using void_t = void();
 using op_t = foo<void>(foo<void>::*)(void_t)&&;

 op_t ops = static_cast<op_t>(&foo<void>::bar<void_t>),
 static_cast<op_t>(&foo<void>::operator;

 for (const auto& op : ops) 
 auto sut = (foo<void>.*op)(());
 // test the behaviour of sut
 

clang e.g., reports me that "the address of overloaded function 'bar' cannot be static_cast to type 'op_t'"

Or am I on the wrong track and this is not possible?
(I tried clang 6 and gcc 7)

I can get the code to compile by changing op_t to

using op_t = foo<void>(foo<void>::*)(void_t &&) &&;
// ^^

and sut to

auto sut = (foo<void>.*op)(*());
// ^

(() can be converted to a function pointer, but *op takes a reference to a function, so we have to dereference the pointer).

Alternatively, instead of changing sut, you can also change void_t to

using void_t = void (*)();
// ^^^

Now void_t is already a function pointer, so you don't have to dereference.