declared Asset trait combining Drop with a getter and setter for an asset id

src/asset.h

@@ -0,0 +1,34 @@
+#ifndef _fencer_asset_h
+#define _fencer_asset_h
+
+#include "drop.h"
+#include "typeclass_helpers.h"
+#include <SDL2/SDL_render.h>
+
+typedef uintptr_t asset_id;
+
+typedef struct {
+    asset_id (*const get_id)(void*);
+    void (*const set_id)(void*, asset_id);
+} IAsset;
+
+typedef struct Asset {
+    void* data;
+    IAsset const* tc;
+    IDrop const* drop;
+} Asset;
+
+#define impl_Asset_for(T, get_id_f, set_id_f)\
+static inline Asset T##_as_Asset(T* x) {\
+    TC_FN_TYPECHECK(asset_id, get_id_f, T*);\
+    TC_FN_TYPECHECK(void, set_id_f, T*, asset_id);\
+    TC_FN_TYPECHECK(Drop, T##_as_Drop, T*);\
+    static IAsset tc = (IAsset){\
+        .get_id = (asset_id(*const)(void*))      get_id_f,\
+        .set_id = (void(*const)(void*,asset_id)) set_id_f,\
+    };\
+    IDrop const* drop = T##_as_Drop(x).tc;\
+    return (Asset){.data=x, .tc=&tc, .drop=drop};\
+}
+
+#endif // !_fencer_asset_h