0

在像下面这样的模板中,如何从另一个更复杂的元组中的元素填充元组?

template<typename... Ts>
struct foo {
  std::tuple<std::vector<Ts>...> tuple;

  foo() {
    //populate tuple somehow
    //assume that no vector is empty
  }

  void func() {
    std::tuple<Ts...> back_tuple; // = ...
    //want to populate with the last elements ".back()" of each vector
    //how?
  }
};

我找不到任何用于元组的 push_back 机制,所以我不确定如何使用模板循环技巧来做到这一点。此外,我找不到任何 initializer_list 之类的模板,用于不同类型来收集我的值,然后传递到新的元组中。有任何想法吗?

4

1 回答 1

3

尝试这样的事情:

std::tuple<std::vector<Ts>...> t;

template <int...> struct Indices {};
template <bool> struct BoolType {};

template <int ...I>
std::tuple<Ts...> back_tuple_aux(BoolType<true>, Indices<I...>)
{
    return std::make_tuple(std::get<I>(t).back()...);  // !!
}

template <int ...I>
std::tuple<Ts...> back_tuple_aux(BoolType<false>, Indices<I...>)
{
    return back_tuple_aux(BoolType<sizeof...(I) + 1 == sizeof...(Ts)>(),
                          Indices<I..., sizeof...(I)>());
};

std::tuple<Ts...> back_tuple()
{
    return back_tuple_aux(BoolType<0 == sizeof...(Ts)>(), Indices<>());
}

(魔法发生在标记的行中!!。)

于 2013-07-08T00:43:53.367 回答