c++ 可变模板参数解包

unpacking_paramater_pack.cpp

#include <iostream>


#if __cplusplus < 201700L
// c++11
template<typename... Args>
constexpr int f(Args&&... args) {
    int sum = 0;
    int arr[] = {(sum+=args, 0)...};
    return sum;
}
#else
// c++17 - fold expression
template<typename... Args>
constexpr int f(Args&&... args) {
    return (args + ...);
}
#endif

struct A {
        constexpr static int a = f(1,2);
};

#define SHOW(expr) \
    std::cout << #expr " = " << expr << std::endl;

int main() {
    SHOW(f(1, 2, 3));
    SHOW(A::a);
    return 0;
}