main.cc

// clang++ -std=c++11 -stdlib=libc++ main.cpp
#include <thread>
#include <vector>
#include <iostream>

using namespace std;

template <typename T> class sum {
    vector<T> &v;
    T &r;
    T a;

public:
    sum(vector<T> &data, T acc, T &result): v(data), a(acc), r(result) {}
    void operator()();
};

template <typename T> void sum<T>::operator()() {
    for (auto i: v) {
        a += i;
    }

    r = a;
}

int main() {
    int result;
    vector<int> data(4, 100);

    thread t(sum<int>(data, 0, result));
    t.join();

    cout << result << endl;
    return 0;
}