From 419af63648b98d848346ecdf7ef6e72fc18bd72d Mon Sep 17 00:00:00 2001
From: Nana Sakisaka <1901813+saki7@users.noreply.github.com>
Date: Thu, 1 Oct 2026 14:51:00 +0900
Subject: [PATCH] Add more container traits

---
 include/iris/container_traits.hpp | 199 +++++++++++++++++++++++-------
 test/container_traits.cpp         |  63 ++++++++++
 2 files changed, 220 insertions(+), 42 deletions(-)

diff --git a/include/iris/container_traits.hpp b/include/iris/container_traits.hpp
index eaa095f..47a0b19 100644
--- a/include/iris/container_traits.hpp
+++ b/include/iris/container_traits.hpp
@@ -41,6 +41,27 @@ concept unique_mapping_container =
     };
 
 
+namespace detail {
+
+template<class T>
+struct element_impl
+{
+    using type = T;
+};
+
+template<class K, class V>
+struct element_impl<std::pair<K const, V>>
+{
+    using type = std::pair<K, V>;
+};
+
+} // detail
+
+// The type of an element made before it is added to `ContainerT`: the value type, whose key is not const
+template<class ContainerT>
+using element_t = detail::element_impl<std::ranges::range_value_t<ContainerT>>::type;
+
+
 namespace detail {
 
 template<class ContainerT>
@@ -108,32 +129,38 @@ template<class R> concept back_accessible = requires(R& r) { back(r); };
 namespace detail {
 
 template<class ContainerT, class... Args>
-concept has_emplace_front =
-    requires(ContainerT& cont) {
-        cont.emplace_front(std::declval<Args>()...);
-    };
+concept emplaceable = std::constructible_from<std::ranges::range_value_t<ContainerT>, Args...>;
 
 template<class ContainerT, class... Args>
-concept has_push_front =
-    sizeof...(Args) == 1 &&
-    requires(ContainerT& cont) {
-        cont.push_front(std::declval<Args>()...);
-    };
+concept position_emplaceable =
+    emplaceable<ContainerT, Args...> &&
+    !requires { typename std::remove_cvref_t<ContainerT>::key_type; };
 
 template<class ContainerT, class... Args>
-concept has_begin_emplace =
-    std::ranges::range<ContainerT> &&
-    requires(ContainerT& cont) {
-        cont.emplace(std::ranges::begin(cont), std::declval<Args>()...);
-    };
+concept has_emplace_front = requires(ContainerT& cont) {
+    requires emplaceable<ContainerT, Args...>;
+    cont.emplace_front(std::declval<Args>()...);
+};
 
 template<class ContainerT, class... Args>
-concept has_begin_insert =
-    sizeof...(Args) == 1 &&
-    std::ranges::range<ContainerT> &&
-    requires(ContainerT& cont) {
-        cont.insert(std::ranges::begin(cont), std::declval<Args>()...);
-    };
+concept has_push_front = requires(ContainerT& cont) {
+    requires sizeof...(Args) == 1;
+    cont.push_front(std::declval<Args>()...);
+};
+
+template<class ContainerT, class... Args>
+concept has_begin_emplace = requires(ContainerT& cont) {
+    requires std::ranges::range<ContainerT>;
+    requires position_emplaceable<ContainerT, Args...>;
+    cont.emplace(std::ranges::begin(cont), std::declval<Args>()...);
+};
+
+template<class ContainerT, class... Args>
+concept has_begin_insert = requires(ContainerT& cont) {
+    requires sizeof...(Args) == 1;
+    requires std::ranges::range<ContainerT>;
+    cont.insert(std::ranges::begin(cont), std::declval<Args>()...);
+};
 
 } // detail
 
@@ -162,7 +189,10 @@ concept prependable =
     front_pushable<ContainerT, Args...> ||
     detail::has_begin_emplace<ContainerT, Args...> ||
     detail::has_begin_insert<ContainerT, Args...> ||
-    (sizeof...(Args) == 0 && default_prependable<ContainerT>);
+    requires {
+        requires sizeof...(Args) == 0;
+        requires default_prependable<ContainerT>;
+    };
 
 namespace detail {
 
@@ -296,32 +326,30 @@ struct prepend_fn
 namespace detail {
 
 template<class ContainerT, class... Args>
-concept has_emplace_back =
-    requires(ContainerT& cont) {
-        cont.emplace_back(std::declval<Args>()...);
-    };
+concept has_emplace_back = requires(ContainerT& cont) {
+    requires emplaceable<ContainerT, Args...>;
+    cont.emplace_back(std::declval<Args>()...);
+};
 
 template<class ContainerT, class... Args>
-concept has_push_back =
-    sizeof...(Args) == 1 &&
-    requires(ContainerT& cont) {
-        cont.push_back(std::declval<Args>()...);
-    };
+concept has_push_back = requires(ContainerT& cont) {
+    requires sizeof...(Args) == 1;
+    cont.push_back(std::declval<Args>()...);
+};
 
 template<class ContainerT, class... Args>
-concept has_end_emplace =
-    std::ranges::range<ContainerT> &&
-    requires(ContainerT& cont) {
-        cont.emplace(std::ranges::end(cont), std::declval<Args>()...);
-    };
+concept has_end_emplace = requires(ContainerT& cont) {
+    requires std::ranges::range<ContainerT>;
+    requires position_emplaceable<ContainerT, Args...>;
+    cont.emplace(std::ranges::end(cont), std::declval<Args>()...);
+};
 
 template<class ContainerT, class... Args>
-concept has_end_insert =
-    sizeof...(Args) == 1 &&
-    std::ranges::range<ContainerT> &&
-    requires(ContainerT& cont) {
-        cont.insert(std::ranges::end(cont), std::declval<Args>()...);
-    };
+concept has_end_insert = requires(ContainerT& cont) {
+    requires sizeof...(Args) == 1;
+    requires std::ranges::range<ContainerT>;
+    cont.insert(std::ranges::end(cont), std::declval<Args>()...);
+};
 
 } // detail
 
@@ -350,7 +378,10 @@ concept appendable =
     back_pushable<ContainerT, Args...> ||
     detail::has_end_emplace<ContainerT, Args...> ||
     detail::has_end_insert<ContainerT, Args...> ||
-    (sizeof...(Args) == 0 && default_appendable<ContainerT>);
+    requires {
+        requires sizeof...(Args) == 0;
+        requires default_appendable<ContainerT>;
+    };
 
 namespace detail {
 
@@ -614,6 +645,90 @@ concept compatible_range =
     std::ranges::input_range<R> &&
     std::convertible_to<std::ranges::range_reference_t<R>, ElemT>;
 
+// ------------------------------------------------------------
+
+namespace detail {
+
+template<class ContainerT, class R>
+concept has_append_range = requires(ContainerT& cont, R&& r) {
+    cont.append_range(std::forward<R>(r));
+};
+
+template<class ContainerT, class R>
+concept has_end_insert_range =
+    std::ranges::range<ContainerT> &&
+    requires(ContainerT& cont, R&& r) {
+        cont.insert_range(std::ranges::end(cont), std::forward<R>(r));
+    };
+
+template<class ContainerT, class R>
+concept has_insert_range = requires(ContainerT& cont, R&& r) {
+    cont.insert_range(std::forward<R>(r));
+};
+
+template<class ContainerT, class R>
+concept has_end_insert_iterators =
+    std::ranges::range<ContainerT> &&
+    std::ranges::common_range<R> &&
+    requires(ContainerT& cont, R& r) {
+        cont.insert(std::ranges::end(cont), std::ranges::begin(r), std::ranges::end(r));
+    };
+
+template<class ContainerT, class R>
+concept has_insert_iterators =
+    std::ranges::common_range<R> &&
+    requires(ContainerT& cont, R& r) {
+        cont.insert(std::ranges::begin(r), std::ranges::end(r));
+    };
+
+// The elements of `r` at the end of `cont`, or into the associative `cont`
+struct append_range_fn
+{
+    template<class ContainerT, class R>
+        requires
+            compatible_range<R, std::ranges::range_value_t<ContainerT>> &&
+            (
+                has_append_range<ContainerT, R> ||
+                has_end_insert_range<ContainerT, R> ||
+                has_insert_range<ContainerT, R> ||
+                has_end_insert_iterators<ContainerT, R> ||
+                has_insert_iterators<ContainerT, R>
+            )
+    static constexpr void operator()(ContainerT& cont, R&& r)
+    {
+        if constexpr (has_append_range<ContainerT, R>) {
+            cont.append_range(std::forward<R>(r));
+
+        } else if constexpr (has_end_insert_range<ContainerT, R>) {
+            cont.insert_range(std::ranges::end(cont), std::forward<R>(r));
+
+        } else if constexpr (has_insert_range<ContainerT, R>) {
+            cont.insert_range(std::forward<R>(r));
+
+        } else if constexpr (has_end_insert_iterators<ContainerT, R>) {
+            cont.insert(std::ranges::end(cont), std::ranges::begin(r), std::ranges::end(r));
+
+        } else {
+            cont.insert(std::ranges::begin(r), std::ranges::end(r));
+        }
+    }
+};
+
+struct clear_fn
+{
+    template<class ContainerT>
+        requires requires(ContainerT& cont) { cont.clear(); }
+    static constexpr void operator()(ContainerT& cont) noexcept(noexcept(cont.clear()))
+    {
+        cont.clear();
+    }
+};
+
+} // detail
+
+[[maybe_unused]] inline constexpr detail::append_range_fn append_range{};
+[[maybe_unused]] inline constexpr detail::clear_fn clear{};
+
 } // iris::container
 
 namespace iris::container::dummy {
diff --git a/test/container_traits.cpp b/test/container_traits.cpp
index 4fdfb88..0590bf0 100644
--- a/test/container_traits.cpp
+++ b/test/container_traits.cpp
@@ -798,3 +798,66 @@ TEST_CASE("container: append")
         STATIC_CHECK(!std::invocable<decltype(iris::container::append_return), Cont&, int, int>);
     }
 }
+
+TEST_CASE("container: append into associative containers")
+{
+    // `emplace(it, x)` of an associative container is a valid expression but not a valid call
+    STATIC_CHECK(iris::container::appendable<std::set<int>, int>);
+    STATIC_CHECK(iris::container::growable_array<std::map<int, int>>);
+
+    std::set<int> s;
+    iris::container::append(s, 2);
+    iris::container::append(s, 1);
+    CHECK(s == std::set<int>{1, 2});
+
+    std::map<int, int> m;
+    iris::container::append(m, std::pair{1, 10});
+    CHECK(m == std::map<int, int>{{1, 10}});
+}
+
+TEST_CASE("container: append_range")
+{
+    std::vector<std::string> source{"a", "b"};
+
+    std::vector<std::string> v{"x"};
+    iris::container::append_range(v, source);
+    CHECK(v == std::vector<std::string>{"x", "a", "b"});
+
+    std::vector<std::string> moved{"x"};
+    iris::container::append_range(moved, source | std::views::as_rvalue);
+    CHECK(moved == std::vector<std::string>{"x", "a", "b"});
+    CHECK(source == std::vector<std::string>{"", ""});
+
+    std::string str = "x";
+    iris::container::append_range(str, "ab"sv);
+    CHECK(str == "xab");
+
+    std::set<int> s{3};
+    iris::container::append_range(s, std::vector{2, 1});
+    CHECK(s == std::set<int>{1, 2, 3});
+
+    std::map<int, int> m{{1, 10}};
+    iris::container::append_range(m, std::vector<std::pair<int, int>>{{2, 20}});
+    CHECK(m == std::map<int, int>{{1, 10}, {2, 20}});
+
+    // `std::vector<int>(std::size_t)` is not a conversion
+    STATIC_CHECK(!std::invocable<decltype(iris::container::append_range), std::vector<std::vector<int>>&, std::vector<int>>);
+    STATIC_CHECK(!std::invocable<decltype(iris::container::append_range), std::array<int, 1>&, std::vector<int>>);
+}
+
+TEST_CASE("container: clear")
+{
+    std::vector<int> v{1, 2};
+    iris::container::clear(v);
+    CHECK(v.empty());
+
+    STATIC_CHECK(!std::invocable<decltype(iris::container::clear), std::array<int, 1>&>);
+    STATIC_CHECK(!std::invocable<decltype(iris::container::clear), std::vector<int> const&>);
+}
+
+TEST_CASE("container: element_t")
+{
+    STATIC_CHECK(std::same_as<iris::container::element_t<std::vector<int>>, int>);
+    STATIC_CHECK(std::same_as<iris::container::element_t<std::map<int, std::string>>, std::pair<int, std::string>>);
+    STATIC_CHECK(std::same_as<iris::container::element_t<std::set<int>>, int>);
+}