VecMapper update with index

framework/base/src/storage/mappers/vec_mapper.rs

@@ -209,6 +209,16 @@ where
         self.set_unchecked(index, item);
     }
 
+    /// Syntactic sugar, to more compactly express a get, update and set in one line.
+    /// Takes whatever lies in storage, apples the given closure and saves the final value back to storage.
+    /// Propagates the return value of the given function.
+    pub fn update<R, F: FnOnce(&mut T) -> R>(&mut self, index: usize, f: F) -> R {
+        let mut value = self.get(index);
+        let result = f(&mut value);
+        self.set(index, &value);
+        result
+    }
+
     /// Keeping `set_unchecked` private on purpose, so developers don't write out of index limits by accident.
     fn set_unchecked(&self, index: usize, item: &T) {
         storage_set(self.item_key(index).as_ref(), item);

framework/scenario/tests/test_vec_mapper.rs

@@ -79,6 +79,20 @@ fn test_vec_swap_remove() {
     check_vec(&vect, vec![42, 45]);
 }
 
+#[test]
+fn test_vec_update() {
+    let mut vect = create_vec();
+
+    vect.extend_from_slice(&[42, 43, 44, 45, 46]);
+
+    assert_eq!(vect.len(), 5);
+    assert_eq!(vect.get(5), 46);
+    vect.update(5, |item| *item = 42);
+    assert_eq!(vect.len(), 5);
+    assert_eq!(vect.get(5), 42);
+    check_vec(&vect, vec![42, 43, 44, 45, 42]);
+}
+
 #[test]
 fn test_vec_iter_processing() {
     let mut vect = create_vec();