Simpler recursive solution. It takes vectors as function arguments, not as a tuple. This version doesn’t build temporary tuples, but uses lambdas instead. Now it makes no unnecessary copies/moves and seems to get optimized successfully.
#include<tuple>
#include<vector>
// cross_imp(f, v...) means "do `f` for each element of cartesian product of v..."
template<typename F>
inline void cross_imp(F f) {
f();
}
template<typename F, typename H, typename... Ts>
inline void cross_imp(F f, std::vector<H> const& h,
std::vector<Ts> const&... t) {
for(H const& he: h)
cross_imp([&](Ts const&... ts){
f(he, ts...);
}, t...);
}
template<typename... Ts>
std::vector<std::tuple<Ts...>> cross(std::vector<Ts> const&... in) {
std::vector<std::tuple<Ts...>> res;
cross_imp([&](Ts const&... ts){
res.emplace_back(ts...);
}, in...);
return res;
}
#include<iostream>
int main() {
std::vector<int> is = {2,5,9};
std::vector<char const*> cps = {"foo","bar"};
std::vector<double> ds = {1.5, 3.14, 2.71};
auto res = cross(is, cps, ds);
for(auto& a: res) {
std::cout << '{' << std::get<0>(a) << ',' <<
std::get<1>(a) << ',' <<
std::get<2>(a) << "}\n";
}
}