From 44f28c5ceafafd88b68de6fe2c05fac332ff3c33 Mon Sep 17 00:00:00 2001
From: Felix Morgner <felix.morgner@ost.ch>
Date: Mon, 17 Aug 2026 14:02:08 +0200
Subject: kstd: implement erase_if for flat map

---
 libs/kstd/kstd/flat_map.hpp       | 23 +++++++++++++++++++++++
 libs/kstd/kstd/flat_map.tests.cpp | 31 +++++++++++++++++++++++++++++++
 2 files changed, 54 insertions(+)

(limited to 'libs')

diff --git a/libs/kstd/kstd/flat_map.hpp b/libs/kstd/kstd/flat_map.hpp
index f3cf827a..e140f7dd 100644
--- a/libs/kstd/kstd/flat_map.hpp
+++ b/libs/kstd/kstd/flat_map.hpp
@@ -1121,6 +1121,13 @@ namespace kstd
       key_compare m_comparator;
     };
 
+    template<typename EKeyType, typename EMappedType, typename EKeyCompare, typename EKeyContainerType,
+             typename EMappedContainerType, typename Predicate>
+    constexpr auto friend erase_if(
+        flat_map<EKeyType, EMappedType, EKeyCompare, EKeyContainerType, EMappedContainerType> & map,
+        Predicate predicate)
+        -> flat_map<EKeyType, EMappedType, EKeyCompare, EKeyContainerType, EMappedContainerType>::size_type;
+
     constexpr auto do_sort() -> void
     {
       auto zipped = std::views::zip(m_containers.keys, m_containers.values);
@@ -1161,6 +1168,22 @@ namespace kstd
       -> flat_map<typename KeyContainer::value_type, typename MappedContainer::value_type, Compare, KeyContainer,
                   MappedContainer>;
 
+  template<typename KeyType, typename MappedType, typename KeyCompare, typename KeyContainerType,
+           typename MappedContainerType, typename Predicate>
+  constexpr auto erase_if(flat_map<KeyType, MappedType, KeyCompare, KeyContainerType, MappedContainerType> & map,
+                          Predicate predicate)
+      -> flat_map<KeyType, MappedType, KeyCompare, KeyContainerType, MappedContainerType>::size_type
+  {
+    auto zipped = std::views::zip(map.m_containers.keys, map.m_containers.values);
+    auto removed = std::ranges::remove_if(zipped, predicate, [](auto const & e) {
+      return
+          typename flat_map<KeyType, MappedType, KeyCompare, KeyContainerType, MappedContainerType>::const_reference{e};
+    });
+    auto count = removed.size();
+    map.erase(map.end() - count, map.end());
+    return count;
+  }
+
 }  // 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 59b5fb99..1c16b5a3 100644
--- a/libs/kstd/kstd/flat_map.tests.cpp
+++ b/libs/kstd/kstd/flat_map.tests.cpp
@@ -388,6 +388,37 @@ SCENARIO("Flat Map modifiers", "[flat_map]")
         REQUIRE(map.size() == old_size);
       }
     }
+
+    WHEN("erasing a single element by predicate")
+    {
+      auto count = erase_if(map, [](auto const & v) { return v.first == 'b'; });
+
+      THEN("one element is removed")
+      {
+        REQUIRE(count == 1);
+        REQUIRE_FALSE(map.contains('b'));
+      }
+
+      THEN("the size is reduced")
+      {
+        REQUIRE(map.size() < old_size);
+      }
+    }
+
+    WHEN("erasing multiple elements by predicate")
+    {
+      auto count = erase_if(map, [](auto const & v) { return v.first == 'b' || v.first == 'f'; });
+
+      THEN("two elements are removed")
+      {
+        REQUIRE(count == 2);
+      }
+
+      THEN("the size is reduced")
+      {
+        REQUIRE(map.size() < old_size);
+      }
+    }
   }
 }
 
-- 
cgit v1.2.3