♻️ add resource_type typename requirement on asset trait

README.md

@@ -246,8 +246,10 @@ resource cache from EnTT, for more information consult
 struct my_asset {
   // ...
 
+  using resource_type = my_asset;
+
   struct loader_type {
-    using result_type = std::shared_ptr<my_asset>;
+    using result_type = std::shared_ptr<resource_type>;
 
     result_type operator()(/* ... */) const {
       // ...
@@ -258,6 +260,54 @@ struct my_asset {
 auto& cache = tw::asset_manager<my_asset>::cache();
 ```
 
+> **NB:** The `resource_type` type name may seem redundant, but it is there for
+> assets that loads the same type of resources, consider the following example:
+
+```cpp
+struct spritesheet {
+  // ...
+};
+
+struct aseprite_sheet {
+  using resource_type = spritesheet;
+
+  struct loader_type {
+    using result_type = std::shared_ptr<resource_type>;
+
+    result_type operator()(/* ... */) const {
+      // ...
+    }
+  };
+};
+
+struct texturepacker_sheet {
+  using resource_type = spritesheet;
+
+  struct loader_type {
+    using result_type = std::shared_ptr<resource_type>;
+
+    result_type operator()(/* ... */) const {
+      // ...
+    }
+  };
+};
+```
+
+Both `aseprite_sheet` and `texturepacker_sheet` assets will return a
+`spritesheet` resource:
+
+```cpp
+auto [it, loaded] = tw::asset_manager<aseprite_sheet>::cache().load(/* ... */);
+auto [id, sheet] = *it;
+// sheet is entt::resource<spritesheet>
+```
+
+```cpp
+auto [it, loaded] = tw::asset_manager<texturepacker_sheet>::cache().load(/* ... */);
+auto [id, sheet] = *it;
+// sheet is entt::resource<spritesheet>
+```
+
 ### Messaging
 
 The message bus is simply a singleton returning an `entt::dispatcher`. For more

include/trollworks/assets.hpp

@@ -8,13 +8,17 @@
 namespace tw {
   template <typename T>
   concept asset_trait = requires(T& asset) {
+    typename T::resource_type;
     typename T::loader_type;
   };
 
   template <asset_trait A>
   class asset_manager {
     public:
-      using cache_type = entt::resource_cache<A, typename A::loader_type>;
+      using cache_type = entt::resource_cache<
+        typename A::resource_type,
+        typename A::loader_type
+      >;
 
       static cache_type& cache() {
         if (!entt::locator<cache_type>::has_value()) {