asset.rs: Use Rc::get_mut to avoid unnecessary clone

Author: alexdewar

src/asset.rs

@@ -286,16 +286,32 @@ impl AssetPool {
     where
         I: IntoIterator<Item = Rc<Asset>>,
     {
-        let new_pool = assets.into_iter().map(|asset| {
+        let new_pool = assets.into_iter().map(|mut asset| {
             if asset.id.is_some() {
                 // Already commissioned
                 asset.into()
             } else {
-                // Newly created from process. We need to assign an ID.
-                let mut asset = asset.as_ref().clone();
-                asset.id = Some(AssetID(self.next_id));
-                self.next_id += 1;
-                asset.into()
+                let mut update_id = |asset: &mut Asset| {
+                    // We need to assign an ID
+                    asset.id = Some(AssetID(self.next_id));
+                    self.next_id += 1;
+                };
+
+                // Asset is newly created from process. We use `get_mut` to avoid a clone in the
+                // (likely) case that there is only one reference to `asset`
+                let rc_asset = match Rc::get_mut(&mut asset) {
+                    Some(asset_inner) => {
+                        update_id(asset_inner);
+                        asset
+                    }
+                    None => {
+                        let mut asset = asset.as_ref().clone();
+                        update_id(&mut asset);
+                        asset.into()
+                    }
+                };
+
+                rc_asset.into()
             }
         });