should I use decltype(auto) or auto for return type?

[JUANDENT]

Hi,

I have this code.. I don't know if operator() should return decltype(auto) or auto.
What is the difference? Which should I use?

template<typename CB>
class CountCalls
{
private:
	CB callback;
	long calls = 0;
public:
	CountCalls(CB cb) : callback(cb) {}
	template<typename ...Args>
	decltype(auto) operator()(Args&&...args)
	{
		++calls;
		return callback(std::forward<Args>(args)...);
	}
	long count() const
	{
		return calls;
	}
};

Regards,
Juan

[TheToaster]

decltype(auto), because your callback could return a cv-qualified value or reference type, and you need to be sure that your function call operator forwards whatever your callback returns to the user.

[JUANDENT]

thanks!!