example: stamp is back

test/example/entity_copy.cpp

@@ -0,0 +1,38 @@
+#include <gtest/gtest.h>
+#include <entt/entity/registry.hpp>
+
+TEST(Example, EntityCopy) {
+    using namespace entt::literals;
+
+    entt::registry registry{};
+    auto &&custom = registry.storage<double>("custom"_hs);
+
+    const auto src = registry.create();
+    const auto dst = registry.create();
+    const auto other = registry.create();
+
+    custom.emplace(src, 1.);
+    registry.emplace<int>(src, 42);
+    registry.emplace<char>(src, 'c');
+    registry.emplace<double>(other, 3.);
+
+    ASSERT_TRUE(custom.contains(src));
+    ASSERT_FALSE(registry.all_of<double>(src));
+    ASSERT_TRUE((registry.all_of<int, char>(src)));
+    ASSERT_FALSE((registry.any_of<int, char, double>(dst)));
+    ASSERT_FALSE(custom.contains(dst));
+
+    registry.visit(src, [src, dst](auto &&storage) {
+        // discard chars because why not, this is just an example after all
+        if(storage.type() != entt::type_id<char>()) {
+            storage.emplace(dst, storage.get(src));
+        }
+    });
+
+    ASSERT_TRUE((registry.all_of<int>(dst)));
+    ASSERT_FALSE((registry.any_of<char, double>(dst)));
+    ASSERT_TRUE(custom.contains(dst));
+
+    ASSERT_EQ(registry.get<int>(dst), 42);
+    ASSERT_EQ(custom.get(dst), 1.);
+}