Almost working save sytem but the data I store is totally wrong. I need to also save the entity IDs being used and map them to the components.

save.cpp

@@ -0,0 +1,63 @@
+#include "save.hpp"
+#include <fstream>
+#include "dbc.hpp"
+#include <fmt/core.h>
+
+using namespace components;
+
+
+template<typename CompT>
+inline void extract(DinkyECS::World &world, std::vector<CompT> &into) {
+  auto from_world = world.entity_map_for<CompT>();
+  for(auto [entity, value] : from_world) {
+    into.push_back(std::any_cast<CompT>(value));
+  }
+}
+
+void save::to_file(std::string path, DinkyECS::World &world) {
+  SaveData save_data;
+  tser::BinaryArchive archive;
+
+  save_data.player = world.get_the<Player>();
+  extract<Position>(world, save_data.position);
+  extract<Combat>(world, save_data.combat);
+  extract<Motion>(world, save_data.motion);
+
+  archive.save(save_data);
+  std::string_view archive_view = archive.get_buffer();
+
+  std::ofstream out(path, std::ios::binary);
+  out << archive_view;
+  out.flush();
+}
+
+
+void save::from_file(std::string path, DinkyECS::World &world_out) {
+  tser::BinaryArchive archive(0);
+
+  if(std::ifstream in_file{path, std::ios::binary | std::ios::ate}) {
+    auto size = in_file.tellg();
+    std::string in_data(size, '\0');
+    in_file.seekg(0);
+
+    if(in_file.read(&in_data[0], size)) {
+      std::string_view in_view(in_data);
+      archive.initialize(in_view);
+    } else {
+      dbc::sentinel(fmt::format("wrong size or error reading {}", path));
+    }
+  } else {
+    dbc::sentinel(fmt::format("failed to load file {}", path));
+  }
+
+  auto save_data = archive.load<SaveData>();
+
+  // BUG: need the entities!
+  world_out.set_the<Player>(save_data.player);
+
+  for(auto position : save_data.position) {
+    auto entity = world_out.entity();
+    // BUG: actually do need the entities
+    world_out.set<Position>(entity, position);
+  }
+}