Qt 5 class parameter as std::function<>

I am having difficulty with some borrowed code that is supposedly working. It contains a class defined like:

Code:

---

#include <functional>
using namespace std;
 
class ClassName
{
public:
    ClassName(parm1 parm, const std::function<double(quint16,quint16)>& func, parm3 param);
};

---

The Qt 5.5 compiler complains:

Quote:

---

function does not name a type

---

and of course, a few errors that cascade after due to this one.

I am not sure what the compiler error is all about. The library <functional> is where the function<> is contained and is included.

What am I missing here?

I can compile without any problem this

Code:

---

class ClassName
{
public:
    ClassName(int x, const std::function<double(quint16,quint16)>& func, int y, int z);
};

---

and inside .pro file I have line

Code:

---

CONFIG += C++14

---