std::function with noexcept in C++17

Question

In C++17 noexcept has been added to the type system:

void r1( void (*f)() noexcept ) { f(); } void foo() { throw 1; }  int main() {     r1(foo); } 

The latest versions of GCC and Clang in C++17 mode reject the call r1(foo), because void (*)() cannot be implicitly converted to void (*)() noexcept.

But with std::function instead:

#include <functional>  void r2( std::function<void() noexcept> f ) { f(); } void foo() { throw 1; }  int main() {     r2(foo); } 

Clang accepts the program, apparently ignoring the noexcept specifier; and g++ gives a strange error regarding std::function<void() noexcept>.

What is the correct behaviour for this second program in C++17?

Answer 1

std::function's definition hasn't changed in the current working draft:

template<class T> class function; // not defined  template<class R, class... ArgTypes> class function<R(ArgTypes...)> {     /* ... */ }; 

Since void() noexcept doesn't match the partial specialization, std::function<void() noexcept> is an incomplete type. Both Clang and GCC trunk diagnose this accordingly.