I would like to filter repeated types from a std::variant like this:
std::variant<int, double, int, std::string, int> -> std::variant<int, double, std::string>
std::variant<std::string, std::string, int> -> std::variant<std::string, int>
How can this be done?
#include <type_traits>
#include <variant>
template <typename T, typename... Ts>
struct filter_duplicates { using type = T; };
template <template <typename...> class C, typename... Ts, typename U, typename... Us>
struct filter_duplicates<C<Ts...>, U, Us...>
: std::conditional_t<(std::is_same_v<U, Ts> || ...)
, filter_duplicates<C<Ts...>, Us...>
, filter_duplicates<C<Ts..., U>, Us...>> {};
template <typename T>
struct unique_variant;
template <typename... Ts>
struct unique_variant<std::variant<Ts...>> : filter_duplicates<std::variant<>, Ts...> {};
template <typename T>
using unique_variant_t = typename unique_variant<T>::type;