Fix major incorrect usage of mrb class definitions causing segfaults

include/app/app.h

@@ -8,7 +8,6 @@
 
 namespace app {
 struct Element {
-  int reference_count = 0;
   Vec2<float> position = {0, 0};
   float rotation = 0;
   Vec2<float> scale = {1, 1};
@@ -21,11 +20,8 @@ struct Element {
   virtual Vec2<float> size(Window *window) = 0;
 
   void click() {
-    if (!mrb_nil_p(on_click.proc)) {
-      int x = mrb_gc_arena_save(Ruby::mrb);
+    if (!mrb_nil_p(on_click.proc))
       on_click.call();
-      mrb_gc_arena_restore(Ruby::mrb, x);
-    }
   }
 };
 
@@ -93,21 +89,15 @@ struct ERect : Element {
   }
 };
 
-inline Pool<Element *> element_pool;
+inline Pool<Element> element_pool;
 
 struct Scene {
-  bool unused = false;
   std::vector<int> element_ids;
   Ruby::Block update;
 
   ~Scene() {
-    for (const int &id : element_ids) {
-      element_pool[id]->reference_count--;
-      if (element_pool[id]->reference_count <= 0) {
-        delete element_pool[id];
-        element_pool.release(id);
-      }
-    }
+    for (const int &id : element_ids)
+      element_pool.release(id);
   }
 
   void add_element(int element_id) {
@@ -116,31 +106,27 @@ struct Scene {
       element_ids.end(),
       element_id,
       [](auto &a, auto &b) {
-        return element_pool[a]->z < element_pool[b]->z || (element_pool[a]->z == element_pool[b]->z && a < b);
+        auto e_a = element_pool[a];
+        auto e_b = element_pool[b];
+        return e_a->z < e_b->z || (e_a->z == e_b->z && a < b);
       }
     );
-    element_pool[element_id]->reference_count++;
+    element_pool.use(element_id);
     element_ids.insert(it, element_id);
   }
 
   void delete_element(int element_id) {
     auto it = std::find(element_ids.begin(), element_ids.end(), element_id);
     if (it != element_ids.end()) {
-      element_pool[element_id]->reference_count--;
-      if (element_pool[element_id]->reference_count <= 0) {
-        delete element_pool[element_id];
-        element_pool.release(element_id);
-      }
+      element_pool.release(element_id);
       element_ids.erase(it);
     }
   }
 
   void update_scene(uint64_t delta_time) {
     if (!mrb_nil_p(update.proc)) {
-      int x = mrb_gc_arena_save(Ruby::mrb);
       mrb_value dt_val = mrb_int_value(Ruby::mrb, delta_time);
       update.call(1, &dt_val);
-      mrb_gc_arena_restore(Ruby::mrb, x);
     }
   }
 
@@ -165,24 +151,15 @@ struct Scene {
   }
 };
 
-inline Pool<Scene *> scene_pool;
+inline Pool<Scene> scene_pool;
 
 struct App {
   int current_scene_id = 0;
   bool running = true;
 
   void switch_to_scene(int scene_id) {
-    int scene_pool_size = (int)scene_pool.all().size();
-    for (int i = 0; i < scene_pool_size; ++i) {
-      auto &val = scene_pool[i];
-      if (i == scene_id && val != nullptr && val->unused)
-        val->unused = false;
-      if (val != nullptr && val->unused) {
-        delete val;
-        scene_pool.release(i);
-      }
-    }
-
+    scene_pool.release(current_scene_id);
+    scene_pool.use(scene_id);
     current_scene_id = scene_id;
   }