storage: added empty ::get method to storage for empty types

src/entt/entity/storage.hpp

@@ -767,6 +767,19 @@ public:
         return allocator_type{base_type::get_allocator()};
     }
 
+    /**
+     * @brief Returns the object assigned to an entity, that is `void`.
+     *
+     * @warning
+     * Attempting to use an entity that doesn't belong to the storage results in
+     * undefined behavior.
+     *
+     * @param entt A valid identifier.
+     */
+    void get([[maybe_unused]] const entity_type entt) const ENTT_NOEXCEPT {
+        ENTT_ASSERT(base_type::contains(entt), "Storage does not contain entity");
+    }
+
     /**
      * @brief Returns an empty tuple.
      *
@@ -992,10 +1005,7 @@ public:
     decltype(auto) emplace(basic_registry<entity_type> &owner, const entity_type entt, Args &&... args) {
         Type::emplace(entt, std::forward<Args>(args)...);
         construction.publish(owner, entt);
-
-        if constexpr(!ignore_as_empty_v<value_type>) {
-            return this->get(entt);
-        }
+        return this->get(entt);
     }
 
     /**
@@ -1032,10 +1042,7 @@ public:
     decltype(auto) patch(basic_registry<entity_type> &owner, const entity_type entt, Func &&... func) {
         Type::patch(entt, std::forward<Func>(func)...);
         update.publish(owner, entt);
-
-        if constexpr(!ignore_as_empty_v<value_type>) {
-            return this->get(entt);
-        }
+        return this->get(entt);
     }
 
 private:

test/entt/entity/storage.cpp

@@ -208,6 +208,7 @@ TEST(Storage, EmptyType) {
 
     ASSERT_NO_THROW([[maybe_unused]] auto alloc = pool.get_allocator());
     ASSERT_TRUE(pool.contains(entt::entity{99}));
+    ASSERT_DEATH(pool.get(entt::entity{}), "");
 }
 
 TEST(Storage, Insert) {