mz_repr/adt/jsonb.rs
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652 653 654 655 656 657 658 659 660 661 662 663 664 665 666 667 668 669 670 671 672 673 674 675 676 677 678 679 680 681 682 683 684 685 686 687 688 689 690 691 692 693 694 695 696 697 698 699 700 701 702 703 704 705 706 707 708 709 710 711 712 713 714 715
// Copyright Materialize, Inc. and contributors. All rights reserved.
//
// Use of this software is governed by the Business Source License
// included in the LICENSE file.
//
// As of the Change Date specified in that file, in accordance with
// the Business Source License, use of this software will be governed
// by the Apache License, Version 2.0.
//! JSON representation.
//!
//! This module provides a [`serde_json`]-like API that is backed by the native
//! Materialize data format, i.e., [`Row`] and [`Datum`]. It supports
//! efficiently parsing and serializing JSON strings and byte slices with
//! minimal allocations. It also provides seamless interop with APIs that
//! require [`serde_json::Value`], though at a small performance cost.
//!
//! There are two core types in the module:
//!
//! * [`Jsonb`] represents owned JSON data. This type houses the
//! deserialization functions.
//!
//! * [`JsonbRef`] is a borrowed view of JSON data. This type houses the
//! serialization functions.
//!
//! The name "jsonb" is based on the PostgreSQL data type of the same name.
//! Various sources claim this stands for "JSON better", as compared to the
//! less-efficient `json` data type in PostgreSQL.
//!
//! ## Constructing JSON objects
//!
//! To parse JSON from a string, use the [`FromStr`] implementation. Once
//! parsed, the underlying [`Row`] can be extracted with [`Jsonb::into_row`].
//!
//! ```
//! # use mz_repr::adt::jsonb::Jsonb;
//! let jsonb: Jsonb = r#"{"a": 1, "b": 2}"#.parse()?;
//! let row = jsonb.into_row();
//! # Ok::<(), Box<dyn std::error::Error>>(())
//! ```
//!
//! If the source JSON is in bytes, use [`Jsonb::from_slice`] instead:
//!
//! ```
//! # use mz_repr::adt::jsonb::Jsonb;
//! let jsonb = Jsonb::from_slice(br#"{"a": 1, "b": 2}"#);
//! # Ok::<(), Box<dyn std::error::Error>>(())
//! ```
//!
//! ## Serializing JSON objects
//!
//! To write a JSON object to a string, use the [`fmt::Display`] implementation.
//! The alternate format produces pretty output.
//!
//! ```
//! # use mz_repr::adt::jsonb::Jsonb;
//! # let jsonb: Jsonb = "null".parse().unwrap();
//! format!("compressed: {}", jsonb);
//! format!("pretty: {:#}", jsonb);
//! ```
//!
//! ## Direct JSON deserialization
//!
//! You can skip [`Jsonb`] entirely and deserialize JSON directly into an
//! existing [`Row`] with [`JsonbPacker`]. This saves an allocation and a
//! copy.
//!
//! ```rust
//! # use mz_repr::adt::jsonb::JsonbPacker;
//! # use mz_repr::{Datum, Row};
//! let mut row = Row::default();
//! let mut packer = row.packer();
//! packer.push(Datum::Int32(42));
//! JsonbPacker::new(&mut packer).pack_str("[1, 2]")?;
//! # Ok::<(), Box<dyn std::error::Error>>(())
//! ```
use std::borrow::Cow;
use std::str::{self, FromStr};
use std::{fmt, io};
use dec::OrderedDecimal;
use serde::de::{self, DeserializeSeed, Deserializer, MapAccess, SeqAccess, Visitor};
use serde::ser::{Serialize, SerializeMap, SerializeSeq, SerializeStruct, Serializer};
use crate::adt::jsonb::vec_stack::VecStack;
use crate::adt::numeric::Numeric;
use crate::{strconv, Datum, Row, RowPacker, SharedRow};
/// An owned JSON value backed by a [`Row`].
///
/// Similar to [`serde_json::Value`], but the conversion to [`Row`] is free.
///
/// All numbers are represented as [`f64`]s. It is not possible to construct a
/// `Jsonb` from a JSON object that contains integers that cannot be represented
/// exactly as `f64`s.
#[derive(Debug, Clone, PartialOrd, Ord, PartialEq, Eq)]
pub struct Jsonb {
row: Row,
}
impl Jsonb {
/// Constructs a new `Jsonb` from a [`serde_json::Value`].
pub fn from_serde_json(val: serde_json::Value) -> Result<Self, anyhow::Error> {
let mut row = Row::default();
JsonbPacker::new(&mut row.packer()).pack_serde_json(val)?;
Ok(Jsonb { row })
}
/// Parses a `Jsonb` from a byte slice `buf`.
///
/// Errors if the slice is not valid JSON.
pub fn from_slice(buf: &[u8]) -> Result<Jsonb, anyhow::Error> {
let binding = SharedRow::get();
let mut row_builder = binding.borrow_mut();
let mut packer = row_builder.packer();
JsonbPacker::new(&mut packer).pack_slice(buf)?;
Ok(Jsonb {
row: row_builder.clone(),
})
}
/// Constructs a [`JsonbRef`] that references the JSON in this `Jsonb`.
pub fn as_ref(&self) -> JsonbRef {
JsonbRef {
datum: self.row.unpack_first(),
}
}
/// Constructs a `Jsonb` from a [`Row`] containing a single [`Datum`].
///
/// Note that `row` is not checked for validity. Not all `Datum`s are
/// valid JSON.
pub fn from_row(row: Row) -> Jsonb {
Jsonb { row }
}
/// Consumes this `Jsonb` and returns the underlying [`Row`].
pub fn into_row(self) -> Row {
self.row
}
/// Returns a reference to the underlying [`Row`].
pub fn row(&self) -> &Row {
&self.row
}
}
impl FromStr for Jsonb {
type Err = anyhow::Error;
fn from_str(s: &str) -> Result<Self, Self::Err> {
let mut row = Row::default();
JsonbPacker::new(&mut row.packer()).pack_str(s)?;
Ok(Jsonb { row })
}
}
impl fmt::Display for Jsonb {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
self.as_ref().fmt(f)
}
}
/// A borrowed JSON value.
///
/// `JsonbRef` is to [`Jsonb`] as [`&str`](prim@str) is to [`String`].
#[derive(Debug, Copy, Clone)]
pub struct JsonbRef<'a> {
datum: Datum<'a>,
}
impl<'a> JsonbRef<'a> {
/// Constructs a `JsonbRef` from a [`Datum`].
///
/// Note that `datum` is not checked for validity. Not all `Datum`s are
/// valid JSON.
pub fn from_datum(datum: Datum) -> JsonbRef {
JsonbRef { datum }
}
/// Unwraps a `JsonbRef` and returns the inner [`Datum`].
pub fn into_datum(self) -> Datum<'a> {
self.datum
}
/// Constructs an owned [`Jsonb`] from this `JsonbRef`.
pub fn to_owned(&self) -> Jsonb {
Jsonb {
row: Row::pack_slice(&[self.datum]),
}
}
/// Serializes the JSON value into the given IO stream.
///
/// # Panics
///
/// Panics if this `JsonbRef` was constructed with a [`Datum`] that is not
/// representable as JSON.
pub fn to_writer<W>(&self, writer: W) -> Result<(), anyhow::Error>
where
W: io::Write,
{
serde_json::to_writer(writer, &JsonbDatum(self.datum))?;
Ok(())
}
/// Constructs an owned [`serde_json::Value`] from this `JsonbRef`.
///
/// # Panics
///
/// Panics if this `JsonbRef` was constructed with a [`Datum`] that is not
/// representable as JSON.
pub fn to_serde_json(&self) -> serde_json::Value {
serde_json::to_value(JsonbDatum(self.datum))
.expect("conversion to serde_json::Value known to be valid")
}
}
impl fmt::Display for JsonbRef<'_> {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
let alternate = f.alternate();
let mut w = WriterFormatter { inner: f };
if alternate {
serde_json::to_writer_pretty(&mut w, &JsonbDatum(self.datum)).map_err(|_| fmt::Error)
} else {
serde_json::to_writer(&mut w, &JsonbDatum(self.datum)).map_err(|_| fmt::Error)
}
}
}
/// A JSON deserializer that decodes directly into an existing [`RowPacker`].
#[derive(Debug)]
pub struct JsonbPacker<'a, 'row> {
packer: &'a mut RowPacker<'row>,
}
impl<'a, 'row> JsonbPacker<'a, 'row> {
/// Constructs a new `JsonbPacker` that will pack into `row`.
pub fn new(packer: &'a mut RowPacker<'row>) -> JsonbPacker<'a, 'row> {
JsonbPacker { packer }
}
/// Packs a [`serde_json::Value`].
pub fn pack_serde_json(self, val: serde_json::Value) -> Result<(), serde_json::Error> {
let mut commands = vec![];
Collector(&mut commands).deserialize(val)?;
pack(self.packer, &commands);
Ok(())
}
/// Parses and packs a JSON-formatted byte slice.
///
/// Errors if the slice is not valid JSON.
pub fn pack_slice(self, buf: &[u8]) -> Result<(), serde_json::Error> {
let mut commands = vec![];
let mut deserializer = serde_json::Deserializer::from_slice(buf);
Collector(&mut commands).deserialize(&mut deserializer)?;
deserializer.end()?;
pack(self.packer, &commands);
Ok(())
}
/// Parses and packs a JSON-formatted string.
///
/// Errors if the string is not valid JSON.
pub fn pack_str(self, s: &str) -> Result<(), serde_json::Error> {
let mut commands = vec![];
let mut deserializer = serde_json::Deserializer::from_str(s);
Collector(&mut commands).deserialize(&mut deserializer)?;
deserializer.end()?;
pack(self.packer, &commands);
Ok(())
}
}
// The magic internal key name that serde_json uses to indicate that an
// arbitrary-precision number should be serialized or deserialized. Yes, this is
// technically private API, but there's no other way to hook into this machinery
// that doesn't involve all the allocations that come with `serde_json::Value`.
// See the comments in `JsonbDatum::Serialize` and `Collector::visit_map` for
// details.
const SERDE_JSON_NUMBER_TOKEN: &str = "$serde_json::private::Number";
// To support arbitrary-precision numbers, serde_json pretends the JSON
// contained a map like the following:
//
// {"$serde_json::private::Number": "NUMBER AS STRING"}
//
// The code here sniffs out that special map and emits just the numeric
// value.
#[derive(Debug)]
pub(crate) enum KeyClass<'de> {
Number,
MapKey(Cow<'de, str>),
}
pub(crate) struct KeyClassifier;
impl<'de> DeserializeSeed<'de> for KeyClassifier {
type Value = KeyClass<'de>;
fn deserialize<D>(self, deserializer: D) -> Result<Self::Value, D::Error>
where
D: serde::Deserializer<'de>,
{
deserializer.deserialize_str(self)
}
}
impl<'de> Visitor<'de> for KeyClassifier {
type Value = KeyClass<'de>;
fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
formatter.write_str("a string key")
}
#[inline]
fn visit_borrowed_str<E>(self, key: &'de str) -> Result<Self::Value, E> {
match key {
SERDE_JSON_NUMBER_TOKEN => Ok(KeyClass::Number),
_ => Ok(KeyClass::MapKey(Cow::Borrowed(key))),
}
}
#[inline]
fn visit_str<E>(self, key: &str) -> Result<Self::Value, E> {
match key {
SERDE_JSON_NUMBER_TOKEN => Ok(KeyClass::Number),
_ => Ok(KeyClass::MapKey(Cow::Owned(key.to_owned()))),
}
}
}
pub(crate) struct NumberParser;
impl<'de> DeserializeSeed<'de> for NumberParser {
type Value = OrderedDecimal<Numeric>;
fn deserialize<D>(self, deserializer: D) -> Result<Self::Value, D::Error>
where
D: serde::Deserializer<'de>,
{
deserializer.deserialize_str(self)
}
}
impl<'de> Visitor<'de> for NumberParser {
type Value = OrderedDecimal<Numeric>;
fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
formatter.write_str("a valid number")
}
#[inline]
fn visit_str<E>(self, value: &str) -> Result<Self::Value, E>
where
E: de::Error,
{
strconv::parse_numeric(value).map_err(de::Error::custom)
}
}
#[derive(Debug)]
enum Command<'de> {
Null,
Bool(bool),
Numeric(OrderedDecimal<Numeric>),
String(Cow<'de, str>),
Array(usize), // further commands
Map(usize), // further commands
}
struct Collector<'a, 'de>(&'a mut Vec<Command<'de>>);
impl<'a, 'de> DeserializeSeed<'de> for Collector<'a, 'de> {
type Value = ();
fn deserialize<D>(self, deserializer: D) -> Result<(), D::Error>
where
D: Deserializer<'de>,
{
deserializer.deserialize_any(self)
}
}
impl<'a, 'de> Visitor<'de> for Collector<'a, 'de> {
type Value = ();
fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
formatter.write_str("a valid JSON datum")
}
#[inline]
fn visit_unit<E>(self) -> Result<(), E> {
self.0.push(Command::Null);
Ok(())
}
#[inline]
fn visit_bool<E>(self, value: bool) -> Result<(), E> {
self.0.push(Command::Bool(value));
Ok(())
}
#[inline]
fn visit_i64<E>(self, value: i64) -> Result<(), E>
where
E: de::Error,
{
self.0.push(Command::Numeric(OrderedDecimal(value.into())));
Ok(())
}
#[inline]
fn visit_u64<E>(self, value: u64) -> Result<(), E>
where
E: de::Error,
{
self.0.push(Command::Numeric(OrderedDecimal(value.into())));
Ok(())
}
#[inline]
fn visit_f64<E>(self, value: f64) -> Result<(), E> {
self.0.push(Command::Numeric(OrderedDecimal(value.into())));
Ok(())
}
#[inline]
fn visit_str<E>(self, value: &str) -> Result<(), E> {
self.0.push(Command::String(Cow::Owned(value.to_owned())));
Ok(())
}
#[inline]
fn visit_borrowed_str<E>(self, value: &'de str) -> Result<(), E> {
self.0.push(Command::String(Cow::Borrowed(value)));
Ok(())
}
#[inline]
fn visit_seq<V>(self, mut visitor: V) -> Result<(), V::Error>
where
V: SeqAccess<'de>,
{
self.0.push(Command::Array(0));
let start = self.0.len();
while visitor.next_element_seed(Collector(self.0))?.is_some() {}
self.0[start - 1] = Command::Array(self.0.len() - start);
Ok(())
}
#[inline]
fn visit_map<V>(self, mut visitor: V) -> Result<(), V::Error>
where
V: MapAccess<'de>,
{
match visitor.next_key_seed(KeyClassifier)? {
Some(KeyClass::Number) => {
let n = visitor.next_value_seed(NumberParser)?;
self.0.push(Command::Numeric(n));
}
Some(KeyClass::MapKey(key)) => {
self.0.push(Command::Map(0));
let start = self.0.len();
self.0.push(Command::String(key));
visitor.next_value_seed(Collector(self.0))?;
while visitor.next_key_seed(Collector(self.0))?.is_some() {
visitor.next_value_seed(Collector(self.0))?;
}
self.0[start - 1] = Command::Map(self.0.len() - start);
}
None => self.0.push(Command::Map(0)),
}
Ok(())
}
}
struct DictEntry<'a> {
key: &'a str,
val: &'a [Command<'a>],
}
fn pack(packer: &mut RowPacker, value: &[Command]) {
let mut buf = vec![];
pack_value(packer, VecStack::new(&mut buf), value);
}
#[inline]
fn pack_value<'a, 'scratch>(
packer: &mut RowPacker,
scratch: VecStack<'scratch, DictEntry<'a>>,
value: &'a [Command<'a>],
) {
match &value[0] {
Command::Null => packer.push(Datum::JsonNull),
Command::Bool(b) => packer.push(if *b { Datum::True } else { Datum::False }),
Command::Numeric(n) => packer.push(Datum::Numeric(*n)),
Command::String(s) => packer.push(Datum::String(s)),
Command::Array(further) => {
let range = &value[1..][..*further];
pack_list(packer, scratch, range);
}
Command::Map(further) => {
let range = &value[1..][..*further];
pack_dict(packer, scratch, range);
}
}
}
/// Packs a sequence of values as an ordered list.
fn pack_list<'a, 'scratch>(
packer: &mut RowPacker,
mut scratch: VecStack<'scratch, DictEntry<'a>>,
mut values: &'a [Command<'a>],
) {
packer.push_list_with(|packer| {
while !values.is_empty() {
let value = extract_value(&mut values);
pack_value(packer, scratch.fresh(), value);
}
})
}
/// Packs a sequence of (key, val) pairs as an ordered dictionary.
///
/// The keys are required to be `Command::String` variants, and
/// the entries in the dictionary are sorted by these strings.
/// Multiple values for the same key are detected and only
/// the last value is kept.
fn pack_dict<'a, 'scratch>(
packer: &mut RowPacker,
mut scratch: VecStack<'scratch, DictEntry<'a>>,
mut entries: &'a [Command<'a>],
) {
while !entries.is_empty() {
if let Command::String(key) = &entries[0] {
entries = &entries[1..];
let val = extract_value(&mut entries);
scratch.push(DictEntry { key, val });
} else {
unreachable!("JSON decoding produced invalid command sequence");
}
}
// Keys must be written in ascending order, per the requirements of our
// `Row` representation. If keys are duplicated, we must keep only the last
// value for the key, as ordered by appearance in the source JSON, per
// PostgreSQL's implementation.
scratch.sort_by_key(|entry| entry.key);
packer.push_dict_with(|packer| {
for i in 0..scratch.len() {
if i == scratch.len() - 1 || scratch[i].key != scratch[i + 1].key {
let DictEntry { key, val } = scratch[i];
packer.push(Datum::String(key));
pack_value(packer, scratch.fresh(), val);
}
}
});
}
/// Extracts a self-contained slice of commands for the next parse node.
fn extract_value<'a>(values: &mut &'a [Command<'a>]) -> &'a [Command<'a>] {
let result = match values[0] {
Command::Array(further) => &values[..further + 1],
Command::Map(further) => &values[..further + 1],
_ => &values[0..1],
};
*values = &values[result.len()..];
result
}
/// A wrapper for [`Datum`] that implements [`Serialize`].
///
/// This is a separate type from `JsonbRef` because the `Serialize`
/// implementation is only valid for use with serde_json. If we implemented it
/// on `JsonbRef` directly, it would be possible to serialize a `JsonbRef` into
/// any serde format, like YAML, but that transformation would not be tested
/// and would likely be invalid.
struct JsonbDatum<'a>(Datum<'a>);
impl Serialize for JsonbDatum<'_> {
fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
where
S: Serializer,
{
match self.0 {
Datum::JsonNull => serializer.serialize_none(),
Datum::True => serializer.serialize_bool(true),
Datum::False => serializer.serialize_bool(false),
Datum::Numeric(n) => {
// To serialize an arbitrary-precision number, we present
// serde_json with the following magic struct:
//
// struct $serde_json::private::Number {
// $serde_json::private::Number: <NUMBER VALUE>,
// }
//
let mut s = serializer.serialize_struct(SERDE_JSON_NUMBER_TOKEN, 1)?;
s.serialize_field(
SERDE_JSON_NUMBER_TOKEN,
&n.into_inner().to_standard_notation_string(),
)?;
s.end()
}
Datum::String(s) => serializer.serialize_str(s),
Datum::List(list) => {
let mut seq = serializer.serialize_seq(None)?;
for e in list.iter() {
seq.serialize_element(&JsonbDatum(e))?;
}
seq.end()
}
Datum::Map(dict) => {
let mut map = serializer.serialize_map(None)?;
for (k, v) in dict.iter() {
map.serialize_entry(k, &JsonbDatum(v))?;
}
map.end()
}
d => unreachable!("not a json-compatible datum: {:?}", d),
}
}
}
/// Implements `io::Write` for `fmt::Formatter`.
struct WriterFormatter<'a, 'b: 'a> {
inner: &'a mut fmt::Formatter<'b>,
}
impl<'a, 'b> io::Write for WriterFormatter<'a, 'b> {
fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
fn io_error<E>(_: E) -> io::Error {
// Error value is dropped by `fmt::Display` implementations above.
io::Error::new(io::ErrorKind::Other, "fmt error")
}
let s = str::from_utf8(buf).map_err(io_error)?;
self.inner.write_str(s).map_err(io_error)?;
Ok(buf.len())
}
fn flush(&mut self) -> io::Result<()> {
Ok(())
}
}
mod vec_stack {
use std::ops::Index;
/// A `VecStack` presents as a stack of [`Vec`]s where only the vector at
/// the top of the stack is accessible. It is backed by a single [`Vec`]
/// whose allocation is reused as elements are added to and dropped from the
/// stack, and so it can be more efficient than allocating individual
/// vectors.
pub struct VecStack<'a, T> {
buf: &'a mut Vec<T>,
i: usize,
}
impl<'a, T> VecStack<'a, T> {
/// Creates a new `VecStack` backed by `buf`.
///
/// The stack starts with a single psuedo-vector.
pub fn new(buf: &'a mut Vec<T>) -> VecStack<'a, T> {
VecStack { buf, i: 0 }
}
/// Adds a new element to the psuedo-vector at the top of the stack.
pub fn push(&mut self, t: T) {
self.buf.push(t)
}
/// Sorts the psuedo-vector at the top of the stack by the key
/// identified by `f`.
pub fn sort_by_key<F, K>(&mut self, f: F)
where
F: FnMut(&T) -> K,
K: Ord,
{
self.buf[self.i..].sort_by_key(f)
}
/// Returns the length of the psuedo-vector at the top of the stack.
pub fn len(&self) -> usize {
self.buf.len() - self.i
}
/// Push a fresh vector onto the stack.
///
/// The returned `VecStack` is a handle to this vector. The
/// psuedo-vector beneath the new vector is inaccessible until the new
/// handle is dropped.
pub fn fresh<'b>(&'b mut self) -> VecStack<'b, T> {
let i = self.buf.len();
VecStack { buf: self.buf, i }
}
}
impl<'a, T> Index<usize> for VecStack<'a, T> {
type Output = T;
fn index(&self, i: usize) -> &Self::Output {
&self.buf[self.i + i]
}
}
impl<'a, T> Drop for VecStack<'a, T> {
fn drop(&mut self) {
self.buf.truncate(self.i)
}
}
}