Question

I want to make functor to generic function, but I get compiler error.
Here is the code:

template <class T>
struct Creator
{
    template <typename...Ts>
    static std::shared_ptr<T> create(Ts&&... vs)
    {
        std::shared_ptr<T> t(new T(std::forward<Ts>(vs)...));
        return t;
    }
};

class Car:
        public Creator<Car>
{
    private:
        friend class Creator<Car>;
        Car()
        {
        }
};

int main()
{
    auto car=Car::create();
    std::function< std::shared_ptr<Car> () > createFn=&Car::create;

    return 0;
}

I get the following error in GCC 4.6.3 on the second statement(the first is OK):

error: conversion from ‘<unresolved overloaded function type>’
       to non-scalar type ‘std::function<std::shared_ptr<Car>()>’ requested

Any hint appreciated.

Answer 1

If the pointer of a template function is needed, the template must be instantiated first.

std::function<std::shared_ptr<Car>()> createFn = &Car::create<>;

This will make it compile on clang++ 3.1, but g++ 4.8 still refuses to compile, which I believe is a bug.

You could provide a lambda function instead:

std::function<std::shared_ptr<Car>()> createFn = []{ return Car::create(); };