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How does one filter duplicate types from a tuple?
For example:
using Tuple = std::tuple<int, double, int, double, std::string, std::string>
using FilteredTuple = without_duplicates<Tuple>;
In which without_duplicates is implemented in such a way that it generates the following FilteredTuple type:
std::tuple<int, double, std::string>
818
Method #1 : Using set() + tuple() This is the most straight forward way to remove duplicates. In this, we convert the tuple to a set, removing duplicates and then converting it back again using tuple().
Formal query languages are based on mathematical relations. Thus no duplicates appear in relations.
#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
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