From e9a59bb0149f7a7e3409fb12dcfbd60eadb9082d Mon Sep 17 00:00:00 2001
From: Michele Caini <michele.caini@gmail.com>
Date: Thu, 11 Aug 2022 12:15:49 +0200
Subject: [PATCH] registry: swap

---
 src/entt/entity/registry.hpp  | 17 +++++++++++++++++
 test/entt/entity/registry.cpp | 30 ++++++++++++++++++++++++++++++
 2 files changed, 47 insertions(+)

diff --git a/src/entt/entity/registry.hpp b/src/entt/entity/registry.hpp
index 5404b08a7..4ff6b1c2b 100644
--- a/src/entt/entity/registry.hpp
+++ b/src/entt/entity/registry.hpp
@@ -425,6 +425,23 @@ public:
         return *this;
     }
 
+    /**
+     * @brief Exchanges the contents with those of a given registry.
+     * @param other Registry to exchange the content with.
+     */
+    void swap(basic_registry &other) {
+        using std::swap;
+        propagate_on_container_swap(free_list.second(), other.free_list.second());
+        swap(free_list.first(), other.free_list.first());
+        swap(pools, other.pools);
+        swap(groups, other.groups);
+        swap(epool, other.epool);
+        swap(vars, other.vars);
+
+        rebind();
+        other.rebind();
+    }
+
     /**
      * @brief Returns the associated allocator.
      * @return The associated allocator.
diff --git a/test/entt/entity/registry.cpp b/test/entt/entity/registry.cpp
index 488f20351..d0620ac82 100644
--- a/test/entt/entity/registry.cpp
+++ b/test/entt/entity/registry.cpp
@@ -396,6 +396,36 @@ TEST(Registry, Move) {
     ASSERT_EQ(test.parent, &registry);
 }
 
+TEST(Registry, Swap) {
+    entt::registry registry;
+    const auto entity = registry.create();
+    owner test{};
+
+    registry.on_construct<int>().connect<&owner::receive>(test);
+    registry.on_destroy<int>().connect<&owner::receive>(test);
+
+    ASSERT_EQ(test.parent, nullptr);
+
+    registry.emplace<int>(entity);
+
+    ASSERT_EQ(test.parent, &registry);
+
+    entt::registry other;
+    other.swap(registry);
+    other.erase<int>(entity);
+
+    registry = {};
+    registry.emplace<int>(registry.create(entity));
+
+    ASSERT_EQ(test.parent, &other);
+
+    registry.swap(other);
+    registry.emplace<int>(entity);
+    registry.emplace<int>(registry.create(entity));
+
+    ASSERT_EQ(test.parent, &registry);
+}
+
 TEST(Registry, ReplaceAggregate) {
     entt::registry registry;
     const auto entity = registry.create();