c++17 example

Wu zhen hai (112)
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'

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#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 (11237)
It looks like you have mixed up the syntax for deduction guides and constructors. 

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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
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