Add custom drop to AssetStorage

amethyst_assets/src/storage.rs

@@ -112,10 +112,21 @@ impl<A: Asset> AssetStorage<A> {
     }
 
     /// Process finished asset data and maintain the storage.
-    pub fn process<F>(&mut self, mut f: F, errors: &Errors)
+    pub fn process<F>(&mut self, f: F, errors: &Errors)
     where
         F: FnMut(A::Data) -> Result<A, BoxedErr>,
     {
+
+        self.process_custom_drop(f, |_| {}, errors);
+    }
+
+    /// Process finished asset data and maintain the storage.
+    /// This calls the `drop_fn` closure for assets that were removed from the storage.
+    pub fn process_custom_drop<F, D>(&mut self, mut f: F, mut drop_fn: D, errors: &Errors)
+        where
+            D: FnMut(A),
+            F: FnMut(A::Data) -> Result<A, BoxedErr>,
+    {
         while let Some(processed) = self.processed.try_pop() {
             let Processed {
                 data,
@@ -148,7 +159,7 @@ impl<A: Asset> AssetStorage<A> {
             let old = self.handles.swap_remove(i);
             let id = i as u32;
             unsafe {
-                self.assets.remove(id);
+                drop_fn(self.assets.remove(id));
             }
             self.bitset.remove(id);
             self.unused_handles.push(old);