c++17 example

[Wu zhen hai]

I have read an example from the book 《c++17 STL cookbook》.
But I can not compile it under g++8.1 with '-std=c++17'

#include <type_traits>

template<class T>
struct sum
{
    T value;
    template<typename ... Ts>
    sum(Ts&& ... values)  -> sum<std::common_type_t<Ts...>> : value{(values + ...)} 
    {}
};

int main()
{}

[Peter87]

It looks like you have mixed up the syntax for deduction guides and constructors.

template<class T>
struct sum
{
    T value;
    template<typename ... Ts>
    sum(Ts&& ... values) : value{(values + ...)} {} // constructor
};

template <typename ... Ts>
sum(Ts&& ... ts) -> sum<std::common_type_t<Ts...>>;  // deduction guide