Ability to remove components

tests/zecsy.cpp

@@ -113,3 +113,19 @@ TEST_CASE("Retrieve a component from an entity and verify its data matches what
 
     REQUIRE(e.get<Name>().value == "super-zecsy!");
 }
+
+TEST_CASE("Remove a component from an entity and verify it is no longer attached")
+{
+    world w;
+
+    auto e = w.make_entity();
+    e.set(ChoosenOne{});
+    REQUIRE_NOTHROW(e.remove<ChoosenOne>());
+
+    REQUIRE_FALSE(e.has<ChoosenOne>());
+
+    e.set(ChoosenOne{});
+    REQUIRE_NOTHROW(w.remove<ChoosenOne>(e));
+
+    REQUIRE_FALSE(w.has<ChoosenOne>(e));
+}

zecsy.hpp

@@ -2,10 +2,10 @@
 #include <cstdint>
 #include <bitset>
 #include <format>
+#include <queue>
 #include <stdexcept>
 #include <typeindex>
 #include <unordered_map>
-#include <new>
 
 #ifndef MAX_ZECSY_ENTITIES
     #define MAX_ZECSY_ENTITIES 65536
@@ -38,6 +38,9 @@ namespace zecsy
 
         template<typename T>
         void set(const T& comp = T{});
+
+        template<typename T>
+        void remove();
     private:
         entity_id id = 0;
         class world* w = nullptr;
@@ -56,6 +59,9 @@ namespace zecsy
 
         template<typename T>
         void set(entity_id e, const T& comp = T{});
+
+        template<typename T>
+        void remove(entity_id e);
     private:
         using comp_index = std::type_index;
         using comp_to_bitset = std::unordered_map<comp_index, zecsy_bits>;
@@ -67,9 +73,13 @@ namespace zecsy
         using comp_to_storage = std::unordered_map<comp_index, 
               std::vector<uint8_t>>;
 
+        using comp_to_reusable_ids = std::unordered_map<comp_index, 
+              std::queue<size_t>>;
+
         comp_to_bitset bitset_dict;
         comp_to_entity_dict entity_dict; 
         comp_to_storage storage_dict;
+        comp_to_reusable_ids reusable_id_queues;
     };
 
     class world final
@@ -93,6 +103,9 @@ namespace zecsy
 
         template<typename T>
         void set(entity_id e, const T& comp = T{});
+
+        template<typename T>
+        void remove(entity_id e);
     private:
         zecsy_bits entities_bitset;
         entity_id entity_counter = 0;
@@ -196,14 +209,28 @@ namespace zecsy
 
         auto& storage = storage_dict[typeid(T)];
 
-        size_t T_size = sizeof(T);
-        size_t old_size = storage.size();
+        auto& reusable_ids = reusable_id_queues[typeid(T)];
 
-        storage.resize(old_size + T_size);
-        void* ptr = &storage[0] + old_size;
-        new(ptr) T(comp);
+        if(reusable_ids.empty())
+        {
+            size_t T_size = sizeof(T);
+            size_t old_size = storage.size();
 
-        entity_dict[typeid(T)][e] = old_size / T_size;
+            storage.resize(old_size + T_size);
+            void* ptr = &storage[0] + old_size;
+            new(ptr) T(comp);
+
+            entity_dict[typeid(T)][e] = old_size / T_size;
+            return;
+        }
+
+        auto index = reusable_ids.front();
+        reusable_ids.pop();
+
+        auto ptr = reinterpret_cast<T*>(&storage[0]);
+        new(ptr + index) T(comp);
+
+        entity_dict[typeid(T)][e] = index;
     }
 
     template<typename T>
@@ -217,4 +244,29 @@ namespace zecsy
     {
         w->set(id, comp);
     }
+
+    template<typename T>
+    inline void component_storage::remove(entity_id e)
+    {
+        if(!has<T>(e))
+        {
+            return;
+        }
+
+        bitset_dict[typeid(T)].reset(e);
+        reusable_id_queues[typeid(T)].push(entity_dict[typeid(T)][e]);
+        entity_dict[typeid(T)].erase(e);
+    }
+
+    template<typename T>
+    inline void world::remove(entity_id e)
+    {
+        storage.remove<T>(e);
+    }
+
+    template<typename T>
+    inline void entity::remove()
+    {
+        w->remove<T>(id);
+    }
 };