From 6d2db29fbc13ac6f58c3e554c53d88fc2a49b8bd Mon Sep 17 00:00:00 2001
From: Nana Sakisaka <1901813+saki7@users.noreply.github.com>
Date: Sun, 27 Sep 2026 01:37:18 +0900
Subject: [PATCH] Improve throughput of type list related metafunctions

---
 include/iris/type_list.hpp | 120 +++++++++++++++++++++++++++++--------
 test/type_list.cpp         |   2 +-
 2 files changed, 97 insertions(+), 25 deletions(-)

diff --git a/include/iris/type_list.hpp b/include/iris/type_list.hpp
index b4f19b5..05484e0 100644
--- a/include/iris/type_list.hpp
+++ b/include/iris/type_list.hpp
@@ -59,20 +59,97 @@ struct concat_type_list<type_list<Ts...>, type_list<Us...>, Rest...>
 
 // ----------------------------------------------------------
 
-namespace detail {
+template<class... Ts>
+struct type_bases : Ts...
+{
+    template<template<class...> class TT>
+    using rebind = TT<Ts...>;
+};
 
 template<class... Ts>
-struct identity_bases : std::type_identity<Ts>...
+    requires (sizeof...(Ts) > 0)
+struct type_bases<std::type_identity<Ts>...> : std::type_identity<Ts>...
 {
     template<template<class...> class TT>
     using rebind = TT<Ts...>;
 };
 
+namespace detail {
+
+template<class Bases, class T>
+struct type_bases_push_back_impl;
+
+template<class... Ts, class T>
+struct type_bases_push_back_impl<type_bases<std::type_identity<Ts>...>, T>
+{
+    using type = type_bases<std::type_identity<Ts>..., std::type_identity<T>>;
+};
+
+} // detail
+
+template<class Bases, class T>
+using type_bases_push_back = detail::type_bases_push_back_impl<Bases, T>::type;
+
+// --------------------------------------------------
+
+template<class... Ts>
+using identity_bases = type_bases<std::type_identity<Ts>...>;
+
 template<class T, class BasesT>
-concept identity_base_of = requires(BasesT* bases) {
+concept has_identity_base = requires(BasesT* bases) {
     static_cast<std::type_identity<T>*>(bases);
 };
 
+// --------------------------------------------------
+
+template<std::size_t I, class T>
+struct indexed_virtual_identity : virtual std::type_identity<T>
+{
+    static void select(std::type_identity<T>*);
+};
+
+template<std::size_t... Is, class... Ts>
+    requires (sizeof...(Ts) > 0)
+struct type_bases<indexed_virtual_identity<Is, Ts>...> : indexed_virtual_identity<Is, Ts>...
+{
+    template<template<class...> class TT>
+    using rebind = TT<Ts...>;
+
+    using indexed_virtual_identity<Is, Ts>::select...;
+};
+
+template<class T, class BasesT>
+concept has_exactly_one_identity_base = requires(std::type_identity<T>* base) {
+    // If multiple bases exist, overload resolution is ambiguous
+    BasesT::select(base);
+};
+
+// --------------------------------------------------
+
+namespace detail {
+
+template<template<std::size_t, class> class IdentityTT, class Indexes, class... Ts>
+struct indexed_identity_bases_impl;
+
+template<template<std::size_t, class> class IdentityTT, std::size_t... Is, class... Ts>
+struct indexed_identity_bases_impl<
+    IdentityTT, std::index_sequence<Is...>, Ts...
+>
+{
+    using type = type_bases<IdentityTT<Is, Ts>...>;
+};
+
+} // detail
+
+template<class... Ts>
+using indexed_virtual_identity_bases = detail::indexed_identity_bases_impl<
+    indexed_virtual_identity, std::index_sequence_for<Ts...>, Ts...
+>::type;
+
+// --------------------------------------------------
+
+namespace detail {
+
 template<class BasesT, class... Ts>
 struct unique_type_list_impl;
 
@@ -83,13 +160,13 @@ struct unique_type_list_impl<BasesT>
 };
 
 template<class BasesT, class T, class... Rest>
-    requires identity_base_of<T, BasesT>
+    requires has_identity_base<T, BasesT>
 struct unique_type_list_impl<BasesT, T, Rest...>
     : unique_type_list_impl<BasesT, Rest...>
 {};
 
 template<class... AcceptedTs, class T, class... Rest>
-    requires (!identity_base_of<T, identity_bases<AcceptedTs...>>)
+    requires (!has_identity_base<T, identity_bases<AcceptedTs...>>)
 struct unique_type_list_impl<identity_bases<AcceptedTs...>, T, Rest...>
     : unique_type_list_impl<identity_bases<AcceptedTs..., T>, Rest...>
 {};
@@ -109,7 +186,7 @@ template<class... Ts>
 struct unique_type_list<type_list<Ts...>>
 {
     using type = detail::unique_type_list_impl<
-        detail::identity_bases<>, Ts...
+        identity_bases<>, Ts...
     >::type::template rebind<type_list>;
 };
 
@@ -248,33 +325,28 @@ inline constexpr std::size_t find_index_v = find_index<T, List>::value;
 
 
 template<class T, class... Ts>
-struct is_in : std::disjunction<std::is_same<T, Ts>...> {};
+struct is_in : std::bool_constant<
+    has_identity_base<T, indexed_virtual_identity_bases<Ts...>>
+>
+{};
 
 template<class T, class... Ts>
-inline constexpr bool is_in_v = is_in<T, Ts...>::value;
+inline constexpr bool is_in_v = has_identity_base<T, indexed_virtual_identity_bases<Ts...>>;
 
 // ----------------------------------------------------------
 
-namespace detail {
-
-template<bool Found, class T, class... Us>
-struct exactly_once_impl : std::bool_constant<Found> {};
-
-template<class T, class U, class... Us>
-struct exactly_once_impl<false, T, U, Us...>
-    : exactly_once_impl<std::is_same_v<T, U>, T, Us...> {};
-
-template<class T, class U, class... Us>
-struct exactly_once_impl<true, T, U, Us...>
-    : std::conditional_t<std::is_same_v<T, U>, std::false_type, exactly_once_impl<true, T, Us...>> {};
-
-} // detail
-
 template<class T, class List>
 struct exactly_once;
 
 template<class T, template<class...> class TT, class... Ts>
-struct exactly_once<T, TT<Ts...>> : detail::exactly_once_impl<false, T, Ts...>
+struct exactly_once<T, TT<Ts...>> : std::false_type
+{
+    static_assert(sizeof...(Ts) > 0);
+};
+
+template<class T, template<class...> class TT, class... Ts>
+    requires has_exactly_one_identity_base<T, indexed_virtual_identity_bases<Ts...>>
+struct exactly_once<T, TT<Ts...>> : std::true_type
 {
     static_assert(sizeof...(Ts) > 0);
 };
diff --git a/test/type_list.cpp b/test/type_list.cpp
index 19bb5e9..9af2ff4 100644
--- a/test/type_list.cpp
+++ b/test/type_list.cpp
@@ -78,7 +78,7 @@ TEST_CASE("pack_indexing")
 TEST_CASE("exactly_once")
 {
     STATIC_CHECK(iris::exactly_once_v<int, type_list<int, float>>);
-    STATIC_CHECK_FALSE(iris::exactly_once_v<int, type_list<int, int>>);
+    STATIC_CHECK(!iris::exactly_once_v<int, type_list<int, int>>);
 }
 
 TEST_CASE("is_in")