#include <initializer_list>
#include <iostream>
#include <iterator>
#include <numeric>
#include <string>
 
template <typename T>
T add_select(const T* arr, std::initializer_list<std::size_t> selection)
{
    using std::begin; using std::end;
    return std::accumulate(begin(selection), end(selection), T(), [=](T a, std::size_t b) { return a + arr[b]; });
}
 
int main()
{
    int p[10] = { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 };
    int sum = add_select(p, { 5, 4, 7 });
    std::cout << sum << '\n';
 
    std::string s[9] = { "abc", "def", "ghi", "jkl", "mno", "pqr", "stu", "vwx", "yz" };
    std::string result = add_select(s, { 2, 4, 6 });
    std::cout << result << '\n';
}

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