merge_entity.cpp

void mergeEntity (entt::registry& source_registry, entt::registry& destination_registry, entt::entity source_entity, entt::entity destination_entity, bool overwrite_components)
{
    for(auto [id, source_storage]: source_registry.storage()) {
        auto destination_storage = destination_registry.storage(id);
        if (destination_storage != nullptr && source_storage.contains(source_entity)) {
            if (! destination_storage->contains(destination_entity)) {
                destination_storage->emplace(destination_entity, source_storage.get(source_entity));
            // If destination already contains the component, then either skip or "overwrite"
            } else if (overwrite_components) {
                destination_storage->erase(destination_entity);
                destination_storage->emplace(destination_entity, source_storage.get(source_entity));
            }
        }
    }
}