using a lambda trampoline - to making a closure into a function ptr.

gistfile1.txt

    // Closure type that runs the original function with the supplied args.
    auto __callable = [&] {
	  std::__invoke(std::forward<_Callable>(__f),
			std::forward<_Args>(__args)...);
    };
    // Trampoline to call the actual fn; we will pass in the closure address.
    void (*__oc_tramp)(void*)
      = [] (void *ca) { (*static_cast<decltype(__callable)*>(ca))(); };


now you can call __oc_tramp ( std::addressof (__callable) )