risingwave_common/types/
cow.rs

1// Copyright 2025 RisingWave Labs
2//
3// Licensed under the Apache License, Version 2.0 (the "License");
4// you may not use this file except in compliance with the License.
5// You may obtain a copy of the License at
6//
7//     http://www.apache.org/licenses/LICENSE-2.0
8//
9// Unless required by applicable law or agreed to in writing, software
10// distributed under the License is distributed on an "AS IS" BASIS,
11// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12// See the License for the specific language governing permissions and
13// limitations under the License.
14
15use super::{Datum, DatumRef, ToDatumRef, ToOwnedDatum};
16
17/// 🐮 A borrowed [`DatumRef`] or an owned [`Datum`].
18///
19/// We do not use [`std::borrow::Cow`] because it requires the borrowed variant
20/// to be a reference, whereas what we have is a [`DatumRef`] with a lifetime.
21///
22/// # Usage
23///
24/// Generally, you don't need to match on the variants of `DatumCow` to access
25/// the underlying datum. Instead, you can...
26///
27/// - call [`to_datum_ref`](ToDatumRef::to_datum_ref) to get a borrowed
28///   [`DatumRef`] without any allocation, which can be used to append to an
29///   array builder or to encode into the storage representation,
30///
31/// - call [`to_owned_datum`](ToOwnedDatum::to_owned_datum) to get an owned
32///   [`Datum`] with potentially an allocation, which can be used to store in a
33///   struct without lifetime constraints.
34#[derive(Debug, Clone)]
35pub enum DatumCow<'a> {
36    Borrowed(DatumRef<'a>),
37    Owned(Datum),
38}
39
40impl PartialEq for DatumCow<'_> {
41    fn eq(&self, other: &Self) -> bool {
42        self.to_datum_ref() == other.to_datum_ref()
43    }
44}
45impl Eq for DatumCow<'_> {}
46
47impl From<Datum> for DatumCow<'_> {
48    fn from(datum: Datum) -> Self {
49        DatumCow::Owned(datum)
50    }
51}
52
53impl<'a> From<DatumRef<'a>> for DatumCow<'a> {
54    fn from(datum: DatumRef<'a>) -> Self {
55        DatumCow::Borrowed(datum)
56    }
57}
58
59impl ToDatumRef for DatumCow<'_> {
60    fn to_datum_ref(&self) -> DatumRef<'_> {
61        match self {
62            DatumCow::Borrowed(datum) => *datum,
63            DatumCow::Owned(datum) => datum.to_datum_ref(),
64        }
65    }
66}
67
68impl ToOwnedDatum for DatumCow<'_> {
69    fn to_owned_datum(self) -> Datum {
70        match self {
71            DatumCow::Borrowed(datum) => datum.to_owned_datum(),
72            DatumCow::Owned(datum) => datum,
73        }
74    }
75}
76
77impl DatumCow<'_> {
78    /// Equivalent to `DatumCow::Owned(Datum::None)`.
79    pub const NULL: DatumCow<'static> = DatumCow::Owned(None);
80}
risingwave_common/types/cow.rs

risingwave_common/types/
cow.rs
