risingwave_common/row/
once.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::{Row, assert_row};
16use crate::types::{DatumRef, ToDatumRef};
17
18/// Row for the [`once`] function.
19#[derive(Debug, PartialEq, Eq, Clone, Copy)]
20pub struct Once<D>(D);
21
22impl<D: ToDatumRef> Row for Once<D> {
23    #[inline]
24    fn datum_at(&self, index: usize) -> DatumRef<'_> {
25        if index == 0 {
26            self.0.to_datum_ref()
27        } else {
28            panic!("index out of bounds: the len of `Once` is 1 but the index is {index}")
29        }
30    }
31
32    #[inline]
33    unsafe fn datum_at_unchecked(&self, _index: usize) -> DatumRef<'_> {
34        // Always ignore the index and return the datum, which is okay for undefined behavior.
35        self.0.to_datum_ref()
36    }
37
38    #[inline]
39    fn len(&self) -> usize {
40        1
41    }
42
43    #[inline]
44    fn iter(&self) -> impl ExactSizeIterator<Item = DatumRef<'_>> {
45        std::iter::once(self.0.to_datum_ref())
46    }
47}
48
49/// Creates a row which contains a single [`Datum`](crate::types::Datum) or [`DatumRef`].
50pub fn once<D: ToDatumRef>(datum: D) -> Once<D> {
51    assert_row(Once(datum))
52}
risingwave_common/row/once.rs

risingwave_common/row/
once.rs
