fix typo & refine doc

Signed-off-by: Bugen Zhao <[email protected]>

src/common/src/types/cow.rs

@@ -15,6 +15,9 @@
 use super::{Datum, DatumRef, ToDatumRef, ToOwnedDatum};
 
 /// 🐮 A borrowed [`DatumRef`] or an owned [`Datum`].
+///
+/// We do not use [`std::borrow::Cow`] because it requires the borrowed variant
+/// to be a reference, whereas what we have is a [`DatumRef`] with a lifetime.
 #[derive(Debug, Clone)]
 pub enum DatumCow<'a> {
     Borrowed(DatumRef<'a>),

src/connector/codec/src/decoder/mod.rs

@@ -61,7 +61,7 @@ pub trait Access {
             .map(ToOwnedDatum::to_owned_datum)
     }
 
-    /// Similar to `access`, but may return a borrowed [`DatumCow::Ref`] to avoid unnecessary allocation.
+    /// Similar to `access`, but may return a borrowed [`DatumCow::Borrowed`] to avoid unnecessary allocation.
     /// If not overridden, it will call forward to `access` and always wrap the result in [`DatumCow::Owned`].
     ///
     /// This should be preferred over `access` for both callers and implementors.