Function as an argument of a constructor of std::function wrapper - c++

Question

I am writing Monitor class for synchronization problem and I would like to implement an 'Entry' class that will wrap a std::function.
I implemented it a bit, used function traits, but right now I am only able to construct Entry objects using prepared std::function object. Attempts to write a constructor that has an plain function as a parameter failed with compiler messages about template argument deduction/substitution and <anonymous> parameter.
The program is working but I am just curious how to implement given constructor, this is my code:
template <class F>
struct FunctionType;
template <class R, class Object, class... Args>
struct FunctionType<R (Object::*)(Args...)> {
typedef R return_type;
};
template <class R, class Object, class... Args>
struct FunctionType<R (Object::*)(Args...) const> {
typedef R return_type;
};
template <class F> class Entry {
std::function<F> internalFunction;
...
public:
template <F> Entry(const F& function){
// It doesn't work.
}
template <F> Entry(const std::function<F> function) :
internalFunction(function) {
}
template<F, class... Arguments>
typename FunctionType<F>::return_type operator()(Arguments... arguments){
return internalFunction(arguments...);
}
};

Answer 1

A couple of things:
template<F>
doesn't make any sense at all. You get the type of F from the template parameter on the class, use that and remove this altogether.
Next, it's probably easier for you to use a trailing return type on your operator() function:
template<class... Arguments>
auto operator()(Arguments... arguments) -> decltype(internalFunction(arguments...))
{
return internalFunction(arguments...);
}
(If you have C++14 you can just use auto).
Live Demo
Here's your fixed class
template <class F> class Entry {
std::function<F> internalFunction;
public:
Entry(const F& function){
// It doesn't work.
}
Entry(const std::function<F> function) :
internalFunction(function) {
}
template<class... Arguments>
auto operator()(Arguments... arguments) -> decltype(internalFunction(arguments...)){
return internalFunction(arguments...);
}
};