c++ - 如何从元组 C++ 中过滤重复类型

Question

如何过滤元组中的重复类型？

例如:

using Tuple = std::tuple<int, double, int, double, std::string, std::string>
using FilteredTuple = without_duplicates<Tuple>;

其中 without_duplicates 的实现方式是生成以下 FilteredTuple 类型:

std::tuple<int, double, std::string>

Answer 1

#include <type_traits>
#include <tuple>

template <typename T, typename... Ts>
struct unique : std::type_identity<T> {};

template <typename... Ts, typename U, typename... Us>
struct unique<std::tuple<Ts...>, U, Us...>
    : std::conditional_t<(std::is_same_v<U, Ts> || ...)
                       , unique<std::tuple<Ts...>, Us...>
                       , unique<std::tuple<Ts..., U>, Us...>> {};

template <typename... Ts>
using unique_tuple = typename unique<std::tuple<>, Ts...>::type;

DEMO