entity: add clone_entity utility - close #1351

Author: skypjack

src/entt/entity/utility.hpp

@@ -1,6 +1,7 @@
 #ifndef ENTT_ENTITY_UTILITY_HPP
 #define ENTT_ENTITY_UTILITY_HPP
 
+#include "../config/config.h"
 #include "../core/fwd.hpp"
 #include "../core/type_traits.hpp"
 #include "../stl/memory.hpp"
@@ -248,6 +249,27 @@ struct sigh_helper<Registry, Type> final: sigh_helper<Registry> {
 template<typename Registry>
 sigh_helper(Registry &) -> sigh_helper<Registry>;
 
+/**
+ * @brief Clones an entity and all its components.
+ * @tparam Entity A valid entity type.
+ * @tparam Args Registry type template parameters.
+ * @param ref A valid reference to a registry.
+ * @param src Source entity to copy from.
+ * @return The newly created entity that is a copy of the given one, if any.
+ */
+template<typename Entity, typename... Args>
+[[nodiscard]] Entity clone_entity(basic_registry<Entity, Args...> &ref, const Entity src) {
+    const auto dst = ref.create();
+
+    for([[maybe_unused]] auto [id, storage]: ref.storage()) {
+        if(storage.contains(src)) {
+            storage.push(dst, storage.value(src));
+        }
+    }
+
+    return dst;
+}
+
 } // namespace entt
 
 #endif

test/entt/entity/utility.cpp

@@ -165,3 +165,39 @@ TEST_F(SighHelper, Functionalities) {
 
     ASSERT_EQ(counter, 6);
 }
+
+TEST(CloneEntity, NullEntity) {
+    entt::registry registry{};
+    const entt::entity entity = entt::null;
+    const auto other = entt::clone_entity(registry, entity);
+
+    ASSERT_NE(entity, other);
+    ASSERT_TRUE(registry.valid(other));
+    ASSERT_TRUE(registry.orphan(other));
+}
+
+TEST(CloneEntity, EmptyEntity) {
+    entt::registry registry{};
+    const auto entity = registry.create();
+    const auto other = entt::clone_entity(registry, entity);
+
+    ASSERT_NE(entity, other);
+    ASSERT_TRUE(registry.valid(other));
+    ASSERT_TRUE(registry.orphan(other));
+}
+
+TEST(CloneEntity, ValidEntity) {
+    entt::registry registry{};
+    const auto entity = registry.create();
+
+    registry.emplace<char>(entity, 'c');
+    registry.emplace<int>(entity, 1);
+
+    const auto other = entt::clone_entity(registry, entity);
+
+    ASSERT_NE(entity, other);
+    ASSERT_TRUE(registry.valid(other));
+    ASSERT_TRUE((registry.all_of<char, int>(other)));
+    ASSERT_EQ(registry.get<char>(other), 'c');
+    ASSERT_EQ(registry.get<int>(other), 1);
+}