From 261fc83ff4f6bd9ee8eee338d2ee5559c2e152c2 Mon Sep 17 00:00:00 2001
From: Felix Morgner <felix.morgner@ost.ch>
Date: Sat, 15 Aug 2026 23:02:22 +0200
Subject: kstd: add more flat map ctor tests

---
 libs/kstd/kstd/bits/concepts.hpp  |  6 ++++
 libs/kstd/kstd/flat_map.hpp       | 16 ++++++++++
 libs/kstd/kstd/flat_map.tests.cpp | 67 ++++++++++++++++++++++++++++++++++++++-
 3 files changed, 88 insertions(+), 1 deletion(-)

diff --git a/libs/kstd/kstd/bits/concepts.hpp b/libs/kstd/kstd/bits/concepts.hpp
index f43f4f55..065b6f07 100644
--- a/libs/kstd/kstd/bits/concepts.hpp
+++ b/libs/kstd/kstd/bits/concepts.hpp
@@ -17,6 +17,12 @@ namespace kstd::bits
     lockable.unlock();
   };
 
+  template<typename SuspectType>
+  concept allocator_like = requires(SuspectType & suspect) {
+    typename SuspectType::value_type;
+    suspect.deallocate(suspect.allocate(1), 1);
+  };
+
 }  // namespace kstd::bits
 
 #endif
diff --git a/libs/kstd/kstd/flat_map.hpp b/libs/kstd/kstd/flat_map.hpp
index b9b05366..3eda42d8 100644
--- a/libs/kstd/kstd/flat_map.hpp
+++ b/libs/kstd/kstd/flat_map.hpp
@@ -1,6 +1,7 @@
 #ifndef KSTD_FLAT_MAP_HPP
 #define KSTD_FLAT_MAP_HPP
 
+#include <kstd/bits/concepts.hpp>
 #include <kstd/os/error.hpp>
 #include <kstd/vector.hpp>
 
@@ -912,10 +913,25 @@ namespace kstd
 
   template<typename KeyContainer, typename MappedContainer,
            typename Compare = std::less<typename KeyContainer::value_type>>
+    requires(!bits::allocator_like<Compare>)
   flat_map(KeyContainer, MappedContainer, Compare = Compare{})
       -> flat_map<typename KeyContainer::value_type, typename MappedContainer::value_type, Compare, KeyContainer,
                   MappedContainer>;
 
+  template<typename KeyContainer, typename MappedContainer, typename Allocator>
+    requires(std::uses_allocator_v<KeyContainer, Allocator> && std::uses_allocator_v<MappedContainer, Allocator>)
+  flat_map(KeyContainer, MappedContainer, Allocator)
+      -> flat_map<typename KeyContainer::value_type, typename MappedContainer::value_type,
+                  std::less<typename KeyContainer::value_type>,  // NOLINT(modernize-use-transparent-functors)
+                  KeyContainer, MappedContainer>;
+
+  template<typename KeyContainer, typename MappedContainer, typename Compare, typename Allocator>
+    requires(!bits::allocator_like<Compare> && std::uses_allocator_v<KeyContainer, Allocator> &&
+             std::uses_allocator_v<MappedContainer, Allocator>)
+  flat_map(KeyContainer, MappedContainer, Compare, Allocator)
+      -> flat_map<typename KeyContainer::value_type, typename MappedContainer::value_type, Compare, KeyContainer,
+                  MappedContainer>;
+
 }  // namespace kstd
 
 #endif
\ No newline at end of file
diff --git a/libs/kstd/kstd/flat_map.tests.cpp b/libs/kstd/kstd/flat_map.tests.cpp
index f3384b90..32dbafb2 100644
--- a/libs/kstd/kstd/flat_map.tests.cpp
+++ b/libs/kstd/kstd/flat_map.tests.cpp
@@ -9,6 +9,7 @@
 #include <functional>
 #include <string>
 #include <type_traits>
+#include <utility>
 
 SCENARIO("Flat Map initialization and construction", "[flat_map]")
 {
@@ -46,11 +47,35 @@ SCENARIO("Flat Map initialization and construction", "[flat_map]")
     {
       auto copy = kstd::flat_map<int, int>{map, kstd::allocator<int>{}};
 
-      THEN("the map compare equal")
+      THEN("the maps compare equal")
       {
         REQUIRE(map == copy);
       }
     }
+
+    WHEN("contstructing by move using an allocator")
+    {
+      auto moved = kstd::flat_map<int, int>{std::move(map), kstd::allocator<int>{}};
+
+      THEN("the moved from map is empty")
+      {
+        REQUIRE(map.empty());
+      }
+
+      THEN("the moved to map contains all elements")
+      {
+        REQUIRE(moved.contains(1));
+        REQUIRE(moved.contains(2));
+        REQUIRE(moved.contains(3));
+      }
+
+      THEN("the moved to map has the correct values for each element")
+      {
+        REQUIRE(moved.at(1) == 10);
+        REQUIRE(moved.at(2) == 20);
+        REQUIRE(moved.at(3) == 30);
+      }
+    }
   }
 
   GIVEN("An unsorted key container and an unsorted value container")
@@ -79,6 +104,46 @@ SCENARIO("Flat Map initialization and construction", "[flat_map]")
         REQUIRE(map.at(5) == 'f');
       }
     }
+
+    WHEN("constructing using the containers and an allocator")
+    {
+      auto map = kstd::flat_map{keys, values, kstd::allocator<int>{}};
+
+      THEN("the flat map has size 6")
+      {
+        REQUIRE(map.size() == 6);
+      }
+
+      THEN("the flat map contains all pairs in order")
+      {
+        REQUIRE(map.at(0) == 'a');
+        REQUIRE(map.at(1) == 'b');
+        REQUIRE(map.at(2) == 'c');
+        REQUIRE(map.at(3) == 'd');
+        REQUIRE(map.at(4) == 'e');
+        REQUIRE(map.at(5) == 'f');
+      }
+    }
+
+    WHEN("constructing using the containers and an allocator and a comparator")
+    {
+      auto map = kstd::flat_map{keys, values, std::less<>{}, kstd::allocator<int>{}};
+
+      THEN("the flat map has size 6")
+      {
+        REQUIRE(map.size() == 6);
+      }
+
+      THEN("the flat map contains all pairs in order")
+      {
+        REQUIRE(map.at(0) == 'a');
+        REQUIRE(map.at(1) == 'b');
+        REQUIRE(map.at(2) == 'c');
+        REQUIRE(map.at(3) == 'd');
+        REQUIRE(map.at(4) == 'e');
+        REQUIRE(map.at(5) == 'f');
+      }
+    }
   }
 
   GIVEN("An unsorted key container and an unsorted value container, with duplicate keys")
-- 
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