store generation on creation

src/engine.rs

@@ -125,6 +125,7 @@ impl From<NewCallArgs> for EngineState {
 pub struct Engine {
     state: EngineState,
     origin: Address,
+    generation: u32,
 }
 
 // TODO: upgrade to Berlin HF
@@ -139,7 +140,12 @@ impl Engine {
     }
 
     pub fn new_with_state(state: EngineState, origin: Address) -> Self {
-        Self { state, origin }
+        let generation = Self::get_generation(&origin);
+        Self {
+            state,
+            origin,
+            generation,
+        }
     }
 
     /// Saves state into the storage.
@@ -520,10 +526,9 @@ impl evm::backend::Backend for Engine {
         Engine::get_code(&address)
     }
 
-    /// Get storage value of address at index.
-    fn storage(&self, address: Address, index: H256) -> H256 {
-        let generation = Self::get_generation(&address);
-        Engine::get_storage(&address, &index, generation)
+    /// Get storage value of address at key.
+    fn storage(&self, address: Address, key: H256) -> H256 {
+        Engine::get_storage(&address, &key, self.generation)
     }
 
     /// Get original storage value of address at index, if available.