sparse_set: ::clear honors the modality of the set

TODO

@@ -5,6 +5,7 @@
 * custom pools example (multi instance, tables, enable/disable, and so on...)
 
 WIP:
+* review pop_at/push_at to avoid multiple calls to page/offset
 * make sparse_set/storage adhere to AllocatorAwareContainer requirements
 * fast-contains for sparse sets (low prio but nice-to-have)
 * runtime components (registry), runtime events (dispatcher/emitter), ...

src/entt/entity/sparse_set.hpp

@@ -920,13 +920,9 @@ public:
      */
     void clear(void *ud = nullptr) {
         for(auto &&entity: *this) {
-            if(entity != tombstone) {
-                in_place_pop(entity, ud);
-            }
+            // honor the modality and filter all tombstones
+            remove(entity, ud);
         }
-
-        free_list = tombstone;
-        count = {};
     }
 
 private:

test/entt/entity/sparse_set.cpp

@@ -454,10 +454,14 @@ TEST(SparseSet, StableErase) {
 
     set.clear();
 
-    ASSERT_EQ(set.size(), 0u);
+    ASSERT_EQ(set.size(), 1u);
     ASSERT_EQ(set.current(entities[2u]), traits_type::to_version(entt::tombstone));
     ASSERT_EQ(set.slot(), 0u);
 
+    set.compact();
+
+    ASSERT_EQ(set.size(), 0u);
+
     set.insert(std::begin(entities), std::end(entities));
     set.erase(entities[2u]);
 
@@ -645,10 +649,14 @@ TEST(SparseSet, StableRemove) {
 
     set.clear();
 
-    ASSERT_EQ(set.size(), 0u);
+    ASSERT_EQ(set.size(), 1u);
     ASSERT_EQ(set.current(entities[2u]), traits_type::to_version(entt::tombstone));
     ASSERT_EQ(set.slot(), 0u);
 
+    set.compact();
+
+    ASSERT_EQ(set.size(), 0u);
+
     set.insert(std::begin(entities), std::end(entities));
 
     ASSERT_EQ(set.remove(entities[2u]), 1u);

test/entt/entity/storage.cpp

@@ -306,6 +306,10 @@ TEST(Storage, StableErase) {
 
     pool.clear();
 
+    ASSERT_EQ(pool.size(), 1u);
+
+    pool.compact();
+
     ASSERT_EQ(pool.size(), 0u);
 
     pool.emplace(entities[0u], stable_type{0});
@@ -440,6 +444,10 @@ TEST(Storage, StableRemove) {
 
     pool.clear();
 
+    ASSERT_EQ(pool.size(), 1u);
+
+    pool.compact();
+
     ASSERT_EQ(pool.size(), 0u);
 
     pool.emplace(entities[0u], stable_type{0});