diff --git a/develop/singles/headers/meta.hpp/meta_all.hpp b/develop/singles/headers/meta.hpp/meta_all.hpp
index 81dd25f..596dd77 100644
--- a/develop/singles/headers/meta.hpp/meta_all.hpp
+++ b/develop/singles/headers/meta.hpp/meta_all.hpp
@@ -513,6 +513,41 @@ namespace meta_hpp::detail
     };
 }
 
+namespace meta_hpp::detail
+{
+    template < typename Key, typename Compare, typename Allocator >
+    typename std::set<Key, Compare, Allocator>::iterator
+    insert_or_assign(std::set<Key, Compare, Allocator>& set,
+        typename std::set<Key, Compare, Allocator>::value_type&& value)
+    {
+        auto&& [position, inserted] = set.insert(std::move(value));
+
+        if ( inserted ) {
+            return position;
+        }
+
+        auto node = set.extract(position++);
+        node.value() = std::move(value);
+        return set.insert(position, std::move(node));
+    }
+
+    template < typename Key, typename Compare, typename Allocator >
+    typename std::set<Key, Compare, Allocator>::iterator
+    insert_or_assign(std::set<Key, Compare, Allocator>& set,
+        const typename std::set<Key, Compare, Allocator>::value_type& value)
+    {
+        auto&& [position, inserted] = set.insert(value);
+
+        if ( inserted ) {
+            return position;
+        }
+
+        auto node = set.extract(position++);
+        node.value() = value;
+        return set.insert(position, std::move(node));
+    }
+}
+
 namespace meta_hpp::detail
 {
     template < typename T >
diff --git a/develop/untests/meta_base/insert_or_assign.cpp b/develop/untests/meta_base/insert_or_assign.cpp
new file mode 100644
index 0000000..741677d
--- /dev/null
+++ b/develop/untests/meta_base/insert_or_assign.cpp
@@ -0,0 +1,106 @@
+/*******************************************************************************
+ * This file is part of the "https://github.com/blackmatov/meta.hpp"
+ * For conditions of distribution and use, see copyright notice in LICENSE.md
+ * Copyright (C) 2021-2023, by Matvey Cherevko (blackmatov@gmail.com)
+ ******************************************************************************/
+
+#include "../meta_untests.hpp"
+
+namespace
+{
+    struct movable_value {
+        int key{};
+        int data{};
+
+        movable_value(int k, int d) : key{k}, data{d} {}
+
+        [[maybe_unused]] movable_value(movable_value&&) = default;
+        [[maybe_unused]] movable_value& operator=(movable_value&&) = default;
+
+        movable_value(const movable_value&) = delete;
+        movable_value& operator=(const movable_value&) = delete;
+
+        [[maybe_unused]]
+        friend bool operator<(const movable_value& l, const movable_value& r) noexcept {
+            return l.key < r.key;
+        }
+
+        [[maybe_unused]]
+        friend bool operator==(const movable_value& l, const movable_value& r) noexcept {
+            return l.key == r.key && l.data == r.data;
+        }
+    };
+
+    struct copyable_value {
+        int key{};
+        int data{};
+
+        [[maybe_unused]]
+        friend bool operator<(const copyable_value& l, const copyable_value& r) noexcept {
+            return l.key < r.key;
+        }
+
+        [[maybe_unused]]
+        friend bool operator==(const copyable_value& l, const copyable_value& r) noexcept {
+            return l.key == r.key && l.data == r.data;
+        }
+    };
+}
+
+TEST_CASE("meta/meta_base/insert_or_assign") {
+    namespace meta = meta_hpp;
+    using meta::detail::insert_or_assign;
+
+    SUBCASE("movable_value/insert") {
+        std::set<movable_value, std::less<>> s;
+        s.insert({1, 10});
+        s.insert({3, 30});
+        CHECK(*insert_or_assign(s, movable_value{2, 20}) == movable_value{2, 20});
+        {
+            std::set<movable_value, std::less<>> s2;
+            s2.insert({1, 10});
+            s2.insert({2, 20});
+            s2.insert({3, 30});
+            CHECK(s == s2);
+        }
+    }
+
+    SUBCASE("movable_value/replace") {
+        std::set<movable_value, std::less<>> s;
+        s.insert({1, 10});
+        s.insert({3, 30});
+        CHECK(*insert_or_assign(s, movable_value{3, 42}) == movable_value{3, 42});
+        {
+            std::set<movable_value, std::less<>> s2;
+            s2.insert({1, 10});
+            s2.insert({3, 42});
+            CHECK(s == s2);
+        }
+    }
+
+    SUBCASE("copyable_value/insert/0") {
+        std::set<copyable_value, std::less<>> s{{1, 10}, {3, 30}};
+        CHECK(*insert_or_assign(s, copyable_value{2, 20}) == copyable_value{2, 20});
+        CHECK(s == std::set<copyable_value, std::less<>>{{1, 10}, {2, 20}, {3, 30}});
+    }
+
+    SUBCASE("copyable_value/insert/1") {
+        std::set<copyable_value, std::less<>> s{{1, 10}, {3, 30}};
+        copyable_value v{2, 20};
+        CHECK(*insert_or_assign(s, v) == v);
+        CHECK(s == std::set<copyable_value, std::less<>>{{1, 10}, {2, 20}, {3, 30}});
+    }
+
+    SUBCASE("copyable_value/replace/0") {
+        std::set<copyable_value, std::less<>> s{{1, 10}, {3, 30}};
+        CHECK(*insert_or_assign(s, copyable_value{3, 42}) == copyable_value{3, 42});
+        CHECK(s == std::set<copyable_value, std::less<>>{{1, 10}, {3, 42}});
+    }
+
+    SUBCASE("copyable_value/replace/1") {
+        std::set<copyable_value, std::less<>> s{{1, 10}, {3, 30}};
+        copyable_value v{3, 42};
+        CHECK(*insert_or_assign(s, v) == v);
+        CHECK(s == std::set<copyable_value, std::less<>>{{1, 10}, {3, 42}});
+    }
+}
diff --git a/headers/meta.hpp/meta_base.hpp b/headers/meta.hpp/meta_base.hpp
index c976a40..39b7da8 100644
--- a/headers/meta.hpp/meta_base.hpp
+++ b/headers/meta.hpp/meta_base.hpp
@@ -12,6 +12,7 @@
 #include "meta_base/cvref_traits.hpp"
 #include "meta_base/fixed_function.hpp"
 #include "meta_base/hash_combiner.hpp"
+#include "meta_base/insert_or_assign.hpp"
 #include "meta_base/is_in_place_type.hpp"
 #include "meta_base/memory_buffer.hpp"
 #include "meta_base/noncopyable.hpp"
diff --git a/headers/meta.hpp/meta_base/insert_or_assign.hpp b/headers/meta.hpp/meta_base/insert_or_assign.hpp
new file mode 100644
index 0000000..8c6f22f
--- /dev/null
+++ b/headers/meta.hpp/meta_base/insert_or_assign.hpp
@@ -0,0 +1,44 @@
+/*******************************************************************************
+ * This file is part of the "https://github.com/blackmatov/meta.hpp"
+ * For conditions of distribution and use, see copyright notice in LICENSE.md
+ * Copyright (C) 2021-2023, by Matvey Cherevko (blackmatov@gmail.com)
+ ******************************************************************************/
+
+#pragma once
+
+#include "base.hpp"
+
+namespace meta_hpp::detail
+{
+    template < typename Key, typename Compare, typename Allocator >
+    typename std::set<Key, Compare, Allocator>::iterator
+    insert_or_assign(std::set<Key, Compare, Allocator>& set,
+        typename std::set<Key, Compare, Allocator>::value_type&& value)
+    {
+        auto&& [position, inserted] = set.insert(std::move(value));
+
+        if ( inserted ) {
+            return position;
+        }
+
+        auto node = set.extract(position++);
+        node.value() = std::move(value);
+        return set.insert(position, std::move(node));
+    }
+
+    template < typename Key, typename Compare, typename Allocator >
+    typename std::set<Key, Compare, Allocator>::iterator
+    insert_or_assign(std::set<Key, Compare, Allocator>& set,
+        const typename std::set<Key, Compare, Allocator>::value_type& value)
+    {
+        auto&& [position, inserted] = set.insert(value);
+
+        if ( inserted ) {
+            return position;
+        }
+
+        auto node = set.extract(position++);
+        node.value() = value;
+        return set.insert(position, std::move(node));
+    }
+}