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✨ Add easy way to select optional implementation #231

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Merged
elbeno merged 1 commit into from
May 30, 2025
Merged

✨ Add easy way to select optional implementation #231

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10 changes: 7 additions & 3 deletions include/stdx/optional.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -15,9 +15,12 @@
namespace stdx {
inline namespace v1 {
template <typename T, typename = void> struct tombstone_traits {
static_assert(
stdx::always_false_v<T>,
"To use stdx::optional you must specialize stdx::tombstone_traits");
using unspecialized = int;
constexpr auto operator()() const {
static_assert(
stdx::always_false_v<T>,
"To use stdx::optional you must specialize stdx::tombstone_traits");
}
};

template <typename T>
Expand Down Expand Up @@ -47,6 +50,7 @@ template <typename T, typename TS = tombstone_traits<T>> class optional {
not stdx::is_specialization_of_v<TS, tombstone_traits>,
"Don't define tombstone traits for plain integral types");
constexpr static inline auto traits = TS{};
using check_specialization_t [[maybe_unused]] = decltype(traits());
T val{traits()};

public:
Expand Down
16 changes: 16 additions & 0 deletions test/optional.cpp
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Expand Up @@ -427,3 +427,19 @@ TEST_CASE("tombstone with non-structural value", "[optional]") {
CHECK(*o == std::string_view{});
}
#endif

#if __cplusplus >= 202002L
namespace {
template <typename T>
using my_optional = stdx::conditional_t<requires {
typename stdx::tombstone_traits<T>::unspecialized;
}, std::optional<T>, stdx::optional<T>>;
} // namespace

TEST_CASE("select optional implementation based on whether tombstone traits "
"are present",
"[optional]") {
static_assert(std::is_same_v<my_optional<S>, stdx::optional<S>>);
static_assert(std::is_same_v<my_optional<int>, std::optional<int>>);
}
#endif