Allow (de)serialization of Cow<'_, T> values#1545
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Lorak-mmk merged 1 commit intoscylladb:mainfrom Jan 20, 2026
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Thanks! I left just a few minor comments.
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| impl<'frame, 'metadata, T: 'frame + ToOwned + ?Sized> DeserializeValue<'frame, 'metadata> | ||
| for Cow<'frame, T> | ||
| where | ||
| &'frame T: DeserializeValue<'frame, 'metadata>, | ||
| { | ||
| fn type_check(typ: &ColumnType) -> Result<(), TypeCheckError> { | ||
| <&T>::type_check(typ).map_err(typck_error_replace_rust_name::<Self>) | ||
| } | ||
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| fn deserialize( | ||
| typ: &'metadata ColumnType<'metadata>, | ||
| v: Option<FrameSlice<'frame>>, | ||
| ) -> Result<Self, DeserializationError> { | ||
| <&T>::deserialize(typ, v) | ||
| .map(Cow::Borrowed) | ||
| .map_err(deser_error_replace_rust_name::<Self>) | ||
| } | ||
| } |
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It's unfortunate that Rust doesn't have lifetime specialization (yes, I know there are big soundness issues with it). It would be great to use the Owned variant when deserializing to Cow<'static, T>, but that's not possible (at least for now).
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In docs/source/data-types/data-types.md there is the following line:
Additionally, BoxandArc serialization and deserialization is supported for all above types.
Could you modify it to also mention Cow?
There is already precedence for doing this for Arc<T> and Box<T>
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There is already precedence for doing this for Arc and Box so this PR merely extends the same functionality to a another stdlib smart pointer.
In particular this is useful for me when doing a maybe borrowed deserialization in serde where the string may or may not need to be owned (depending on whether the string was escaped in the input). This maybe borrowed deserialization is done by storing it in a
Cow<'_, str>. I want to then store thatCow<'_, str>asTEXTin Scylla without too much work but prior to this PR that was not doable.While I personally only care about serializing
Cow<'_, str>I figured the driver should be more general and allow for any T and for both serialization and deserialization as it is done for Arc and Box. The main difference is that I didn't need to special case Cow as a generic implementation works just fine.Pre-review checklist
./docs/source/.Fixes:annotations to PR description.