CODEWITHSUNDEEP
c++c++11templates
Llopeth
Llopeth

Reputation: 406

Call std::functions

I am trying to write a class template that would get two std::functions in the constructor parameter and call them upon construction and destruction, in a RAII style.

What am I missing?

template <class T>
class HelloGoodbye{
public:
HelloGoodbye(std::function<T> const & f, std::function<T> const &g)
  :mf(f),mg(g)
{
  mf();
}


~HelloGoodBye()
{
  mg();
}

private:
std::function<T> mf;
std::function<T> mg;
};


class Printer
{
    public:
    void hello()
    {
        std::cout << "hello!" << std::endl;
    }
    void goodbye()
    {
        std::cout << "Goodbye!" << std::endl;   
    }
};

int main()
{
      Printer p;
      auto hi = std::bind(&Printer::hello, &p);
      auto bye = std::bind(&Printer::goodbye, &p);
      HelloGoodbye hgb(hi,bye);      
}

Upvotes: 3

Views: 4056

Answers (2)

max66
max66

Reputation: 66210

You can explicit the template type of hgb, as suggested by songyuanyao, or you can create a make function 

template <typename T>
HelloGoodbye<T> makeHG (std::function<T> const & hi,
                        std::function<T> const & bye)
 { return { hi, bye }; }

and, using auto, you can initialize hgb as follows

auto hgb = makeHG(hi, bye);

Unfortunately, std::bind is a strange beast with an undefined return value, so you can't pass the type returned from std::bind to makeHG() to obtain the T type deduction.

So, if you want to use makeHG(), you can use auto to define hi and bye but you have to explict the type as follows

  std::function<void()> hi = std::bind(&Printer::hello, &p);
  std::function<void()> bye = std::bind(&Printer::goodbye, &p);

So, I suppose, the sonyuanyao one is a better solution.

Upvotes: 0

songyuanyao
songyuanyao

Reputation: 172934

HelloGoodbye is a class template, you need to specify the template argument when use it. e.g.

HelloGoodbye<void()> hgb(hi,bye);

LIVE

BTW: I suppose ~HelloGoodBye() is a typo of ~HelloGoodbye().

Upvotes: 3

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