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🎨 Improve type shrinking and apply it to type_map #328

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Merged
elbeno merged 2 commits into from
Feb 12, 2026
Merged

🎨 Improve type shrinking and apply it to type_map #328

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15b91b2
:art: Improve type shrink/expand
elbeno Feb 10, 2026
1b06a2d
:art: Shrink `type_map` symbols
elbeno Feb 10, 2026
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35 changes: 33 additions & 2 deletions include/stdx/type_traits.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -228,12 +228,43 @@ template <typename T>
constexpr auto is_cx_value_v<T, std::void_t<typename T::cx_value_t>> = true;

#if __cplusplus >= 202002L
namespace detail {
template <typename T> struct shrinkwrap {
using is_shrinkwrapped = void;
using type = T;
};

template <typename T>
using shrink_t = decltype([]() -> T (*)() { return nullptr; });
concept is_shrinkwrapped = requires { typename T::is_shrinkwrapped; };

template <typename T> using expand_t = decltype(T{}()());
template <typename T,
auto F = []()->auto (*)() -> shrinkwrap<T> { return nullptr; }>
CONSTEVAL auto shrink() {
return F;
}

template <typename T>
concept is_shrunk = requires(T t) {
{ t()() } -> is_shrinkwrapped;
};

template <typename T> CONSTEVAL auto maybe_expand() -> T;
template <is_shrunk T>
CONSTEVAL auto maybe_expand() -> typename decltype(T{}()())::type;
} // namespace detail

template <typename T> CONSTEVAL auto shrink() -> decltype(detail::shrink<T>());

template <typename T>
CONSTEVAL auto expand() -> decltype(detail::maybe_expand<T>());
#else
template <typename T> CONSTEVAL auto shrink() -> T;
template <typename T> CONSTEVAL auto expand() -> T;
#endif

template <typename T> using shrink_t = decltype(shrink<T>());
template <typename T> using expand_t = decltype(expand<T>());

STDX_PRAGMA(diagnostic push)
#ifdef __clang__
STDX_PRAGMA(diagnostic ignored "-Wunknown-warning-option")
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22 changes: 11 additions & 11 deletions include/stdx/utility.hpp
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Expand Up @@ -29,6 +29,8 @@ namespace detail {
template <auto V> struct value_t {
constexpr static inline auto value = V;
};

template <typename... Ts> struct type_map : Ts... {};
} // namespace detail

template <typename K, typename V> struct type_pair {
Expand All @@ -43,7 +45,7 @@ template <typename K, auto V> using tv_pair = tt_pair<K, detail::value_t<V>>;
template <auto K, auto V>
using vv_pair = tt_pair<detail::value_t<K>, detail::value_t<V>>;

template <typename... Ts> struct type_map : Ts... {};
template <typename... Ts> using type_map = shrink_t<detail::type_map<Ts...>>;

namespace detail {
template <typename K, typename Default>
Expand All @@ -58,20 +60,19 @@ constexpr static auto reverse_lookup(type_pair<K, V>) -> K;
} // namespace detail

template <typename M, typename K, typename Default = void>
using type_lookup_t = decltype(detail::lookup<K, Default>(std::declval<M>()));
using type_lookup_t = decltype(detail::lookup<K, Default>(expand<M>()));

template <typename M, typename V, typename Default = void>
using reverse_type_lookup_t =
decltype(detail::reverse_lookup<V, Default>(std::declval<M>()));
decltype(detail::reverse_lookup<V, Default>(expand<M>()));

template <typename M, auto K, typename Default = void>
using value_lookup_t =
decltype(detail::lookup<detail::value_t<K>, Default>(std::declval<M>()));
decltype(detail::lookup<detail::value_t<K>, Default>(expand<M>()));

template <typename M, auto V, typename Default = void>
using reverse_value_lookup_t =
decltype(detail::reverse_lookup<detail::value_t<V>, Default>(
std::declval<M>()));
decltype(detail::reverse_lookup<detail::value_t<V>, Default>(expand<M>()));

namespace detail {
template <typename T>
Expand All @@ -81,27 +82,26 @@ using is_not_void = std::bool_constant<not std::is_void_v<T>>;
template <typename M, typename K, auto Default = 0>
constexpr static auto type_lookup_v =
type_or_t<detail::is_not_void,
decltype(detail::lookup<K, void>(std::declval<M>())),
decltype(detail::lookup<K, void>(expand<M>())),
detail::value_t<Default>>::value;

template <typename M, typename V, auto Default = 0>
constexpr static auto reverse_type_lookup_v =
type_or_t<detail::is_not_void,
decltype(detail::reverse_lookup<V, void>(std::declval<M>())),
decltype(detail::reverse_lookup<V, void>(expand<M>())),
detail::value_t<Default>>::value;

template <typename M, auto K, auto Default = 0>
constexpr static auto value_lookup_v =
type_or_t<detail::is_not_void,
decltype(detail::lookup<detail::value_t<K>, void>(
std::declval<M>())),
decltype(detail::lookup<detail::value_t<K>, void>(expand<M>())),
detail::value_t<Default>>::value;

template <typename M, auto V, auto Default = 0>
constexpr static auto reverse_value_lookup_v =
type_or_t<detail::is_not_void,
decltype(detail::reverse_lookup<detail::value_t<V>, void>(
std::declval<M>())),
expand<M>())),
detail::value_t<Default>>::value;

#if __cpp_lib_forward_like < 202207L
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6 changes: 3 additions & 3 deletions test/type_traits.cpp
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Expand Up @@ -255,9 +255,9 @@ TEST_CASE("type shrinkage", "[type_traits]") {
using B = long_type_name<A, A, A, A, A, A, A, A>;
using C = long_type_name<B, B, B, B, B, B, B, B>;
using X = stdx::shrink_t<C>;
STATIC_REQUIRE(stdx::type_as_string<X>().size() <
stdx::type_as_string<C>().size());
STATIC_REQUIRE(std::same_as<stdx::expand_t<X>, C>);
STATIC_CHECK(stdx::type_as_string<X>().size() <
stdx::type_as_string<C>().size());
STATIC_CHECK(std::same_as<stdx::expand_t<X>, C>);
}
#endif

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