9

With my compiler 

typedef const double&(*fT)(const double&, const double&);
typedef std::function<const double&(const double&, const double&)> std_func;

fT f1 = std::max<double>;                            //(1)
std_func f2 = static_cast<fT>(std::max<double>);     //(2)
std_func f3 = f1;                                    //(3)

(1, 2, 3) work but 

auto f4 = std::max<double>;                          //(4)
std_func f5 = std::max<double>;                      //(5)

(4, 5) don't. The compiler complains about its incapability to choose the overload for case 5.

Is this behavior normal?

What is the most portable and correct way to write it?

Martin Bonner supports Monica
  • 28,528
  • 3
  • 51
  • 88
jimifiki
  • 5,377
  • 2
  • 34
  • 60
  • 1
    What are you trying to achieve? – Slava May 29 '18 at 14:27
  • @Slava I'm trying to fix the compiling errors of an old code base on one more compiler. The old code was (5). I fixed it by writing (3). Thx for your commen, an answer is welcome :-) – jimifiki May 29 '18 at 14:32
  • I think then you should rephrase your question as how to make (5) compile and what variants you tried, as it is written it is not clear at all – Slava May 29 '18 at 14:39

1 Answers1

12

There are two possible overloads of instantiation of std::max<double>: std::max(double, double) and std::max(std::initializer_list<double>). Because of that, versions 4 and 5 fail, since it can't figure out which overload matches.

Cases 1, 2 and 3 succeed because of the special rules - when taking an address of overload function, type of the result is used to select the proper overload.

SergeyA
  • 61,605
  • 5
  • 78
  • 137