http://ideone.com/ThhAoa
没那么棘手:
#include <cstddef>
#include <utility>
#include <vector>
#include <tuple>
#include <string>
#include <iostream>
using std::size_t;
template<size_t...> struct seq {};
template<size_t Min, size_t Max, size_t... s>
struct make_seq:make_seq< Min, Max-1, Max-1, s... > {};
template<size_t Min, size_t... s>
struct make_seq< Min, Min, s... > {
typedef seq<s...> type;
};
template<size_t Max, size_t Min=0>
using MakeSeq = typename make_seq<Min, Max>::type;
size_t product_size() {
return 1;
}
template<typename... Sizes>
size_t product_size( size_t x, Sizes... tail ) {
return x * product_size(tail...);
}
namespace details {
template<typename max_iterator, typename Lambda>
void for_each_index( max_iterator mbegin, max_iterator mend, Lambda&& f, std::vector<size_t>& idx ) {
if (mbegin == mend) {
f(idx);
} else {
for (size_t i = 0; i < *mbegin; ++i) {
idx.push_back(i);
for_each_index(mbegin+1, mend, f, idx);
idx.pop_back();
}
}
}
template<typename Lambda>
void for_each_index( std::vector<size_t> const& maxes, Lambda&& f ) {
std::vector<size_t> idx;
details::for_each_index( maxes.begin(), maxes.end(), f, idx );
}
template<size_t... s, typename... Ts>
std::vector< std::tuple<Ts...> > does_it_blend( seq<s...>, std::tuple< std::vector<Ts>... >const& input ) {
std::vector< std::tuple<Ts...> > retval;
retval.reserve( product_size( std::get<s>(input).size()... ) );
std::vector<size_t> maxes = {
(std::get<s>(input).size())...
};
for_each_index( maxes, [&](std::vector<size_t> const& idx){
retval.emplace_back( std::get<s>(input)[idx[s]]... );
});
return retval;
}
}
template<typename... Ts>
std::vector< std::tuple<Ts...> > does_it_blend( std::tuple< std::vector<Ts>... >const& input ) {
return details::does_it_blend( MakeSeq< sizeof...(Ts) >(), input );
}
int main() {
std::tuple< std::vector<int>, std::vector<bool>, std::vector<std::string> > input {
{ 1, 2, 3}, { false, true}, { "Hello", "World"}
};
// should become 3 x 2 x 2 = 12 cases { {1, false, "Hello"}, ... , {3, true, "World"} }
std::vector< std::tuple<int, bool, std::string> > test_cases = does_it_blend( input );
for( auto&& x:test_cases ) {
std::cout << std::get<0>(x) << "," << std::get<1>(x) << "," << std::get<2>(x) << "\n";
}
}
在这里,我创建了一个函数,它对可能的索引进行笛卡尔积,然后直接在输出容器中创建元组。
我还费心保留输出大小。
现在用更少的代码。