[英]how select multiple elements from a tuple by several types in C++?
這是我的代碼, a
應該獲取類型為std::tuple<int,bool>
的變量。 但是,它不起作用。 那么,到底出了什么問題以及如何解決呢?
#include <vector>
#include <tuple>
template <class... Ts>
class vector_df {
public:
std::tuple<std::vector<Ts>...> data;
template <class... As>
auto select() {
return std::make_tuple(std::get<As>(data)...);
}
};
int main() {
vector_df<int,char,bool> df;
auto a = df.select<int,bool>();
return 0;
}
這是在線 C++ IDE 上的代碼鏈接。https://godbolt.org/z/BwzvCZ錯誤消息:
/opt/compiler-explorer/gcc-9.1.0/include/c++/9.1.0/tuple: In instantiation of 'constexpr _Tp& std::get(std::tuple<_Elements ...>&) [with _Tp = int; _Types = {std::vector<int, std::allocator<int> >, std::vector<char, std::allocator<char> >, std::vector<bool, std::allocator<bool> >}]':
<source>:11:38: required from 'auto vector_df<Ts>::select() [with As = {int, bool}; Ts = {int, char, bool}]'
<source>:17:34: required from here
/opt/compiler-explorer/gcc-9.1.0/include/c++/9.1.0/tuple:1365:37: error: no matching function for call to '__get_helper2<int>(std::tuple<std::vector<int, std::allocator<int> >, std::vector<char, std::allocator<char> >, std::vector<bool, std::allocator<bool> > >&)'
1365 | { return std::__get_helper2<_Tp>(__t); }
| ~~~~~~~~~~~~~~~~~~~~~~~^~~~~
auto a = df.select<int,bool>();
此模板 function 的參數是int
和bool
。
但很明顯,您的data
元組包含其中的std::vector
,因此您的select()
方法應該是:
template <class... As>
auto select() {
return std::make_tuple(std::get<std::vector<As>>(data)...);
}
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