mz_repr/
fixed_length.rs

1// Copyright Materialize, Inc. and contributors. All rights reserved.
2//
3// Use of this software is governed by the Business Source License
4// included in the LICENSE file.
5//
6// As of the Change Date specified in that file, in accordance with
7// the Business Source License, use of this software will be governed
8// by the Apache License, Version 2.0.
9
10//! Provides abstractions for types that can append their datums to a vector.
11//! `Row` is the most obvious implementor, but other trace types that may use more advanced
12//! representations only need to commit to implementing this trait.
13
14use crate::{Datum, Row, RowArena};
15
16/// A helper trait for types that can append their datums to a `Vec<Datum>`.
17pub trait ExtendDatums {
18    /// Append datums to `target` — all of them (`max == None`) or at most
19    /// `max` (`Some`) — branching on representation ONCE rather than once per
20    /// datum.
21    ///
22    /// `arena` provides storage for data that the appended datums borrow from
23    /// but that does not already live in `self`. Representations backed directly
24    /// by packed bytes (`Row`, row-spine's `DatumSeq`) ignore it, while
25    /// compressed representations can decode into it so the resulting
26    /// `Datum<'a>`s borrow from the arena rather than from `self`. Implementors
27    /// should push directly into `target` in a tight loop, branching on their
28    /// representation once rather than once per datum.
29    fn extend_datums<'a>(
30        &'a self,
31        arena: &'a RowArena,
32        target: &mut Vec<Datum<'a>>,
33        max: Option<usize>,
34    );
35}
36
37impl<T: ExtendDatums + ?Sized> ExtendDatums for &T {
38    #[inline]
39    fn extend_datums<'a>(
40        &'a self,
41        arena: &'a RowArena,
42        target: &mut Vec<Datum<'a>>,
43        max: Option<usize>,
44    ) {
45        // Forward to T's impl so an override isn't lost behind a reference.
46        (**self).extend_datums(arena, target, max)
47    }
48}
49
50// Identity implementation for Row, whose datums borrow directly from its bytes.
51impl ExtendDatums for Row {
52    #[inline]
53    fn extend_datums<'a>(
54        &'a self,
55        _arena: &'a RowArena,
56        target: &mut Vec<Datum<'a>>,
57        max: Option<usize>,
58    ) {
59        match max {
60            Some(max) => target.extend(self.iter().take(max)),
61            None => target.extend(self.iter()),
62        }
63    }
64}
mz_repr/fixed_length.rs

mz_repr/
fixed_length.rs
