Make IntoOwnedRow cache generic

Author: momobel

diesel/src/row.rs

@@ -3,8 +3,8 @@
 use crate::backend::Backend;
 use crate::deserialize;
 use deserialize::FromSql;
+use std::default::Default;
 use std::ops::Range;
-use std::sync::Arc;
 
 #[cfg(feature = "i-implement-a-third-party-backend-and-opt-into-breaking-changes")]
 #[doc(inline)]
@@ -157,8 +157,11 @@ pub trait IntoOwnedRow<'a, DB: Backend>: Row<'a, DB> {
     /// The owned version of the row
     type OwnedRow: Row<'a, DB> + Send + 'static;
 
+    /// A store for cached information between rows for faster access
+    type Cache: Default + 'static;
+
     /// Turn the row into its owned version
-    fn into_owned(self, column_name_cache: &mut Option<Arc<[Option<String>]>>) -> Self::OwnedRow;
+    fn into_owned(self, cache: &mut Self::Cache) -> Self::OwnedRow;
 }
 
 // These traits are not part of the public API

diesel/src/sqlite/connection/row.rs

@@ -26,7 +26,9 @@ pub(super) enum PrivateSqliteRow<'stmt, 'query> {
 impl<'stmt> IntoOwnedRow<'stmt, Sqlite> for SqliteRow<'stmt, '_> {
     type OwnedRow = OwnedSqliteRow;
 
-    fn into_owned(self, column_name_cache: &mut Option<Arc<[Option<String>]>>) -> Self::OwnedRow {
+    type Cache = Option<Arc<[Option<String>]>>;
+
+    fn into_owned(self, column_name_cache: &mut Self::Cache) -> Self::OwnedRow {
         self.inner.borrow().moveable(column_name_cache)
     }
 }