Enum zerovec::ZeroVec

#[non_exhaustive]
pub enum ZeroVec<'a, T: ?Sized> where
    T: AsULE,  {
    Owned(Vec<T::ULE>),
    Borrowed(&'a [T::ULE]),
}

A zero-copy vector for fixed-width types.

ZeroVec<T> is designed as a drop-in replacement for Vec<T> in situations where it is desirable to borrow data from an unaligned byte slice, such as zero-copy deserialization.

T must implement AsULE, which is auto-implemented for a number of built-in types, including all fixed-width multibyte integers.

How it Works

ZeroVec<T> represents a slice of T as a slice of T::ULE. The difference between T and T::ULE is that T::ULE must be encoded in little-endian with 1-byte alignment. When accessing items from ZeroVec<T>, we fetch the T::ULE, convert it on the fly to T, and return T by value.

Benchmarks can be found in the project repository. We found that for common operations on small and large vectors, ZeroVec<T> performs from slightly faster to 15% slower than Vec<T>. However, the main performance improvement on ZeroVec<T> is when deserializing from a byte array; ZeroVec<T> deserializes 80% faster than Vec<T> in Serde Bincode, and it does not require any heap allocations.

Safety

ZeroVec<T> contains no unsafe code. However, the conversion from &[u8] to &[T::ULE] may be unsafe. For more information, see the ule module.

Example

use zerovec::ZeroVec;

// The little-endian bytes correspond to the numbers on the following line.
let bytes: &[u8] = &[0xD3, 0x00, 0x19, 0x01, 0xA5, 0x01, 0xCD, 0x01];
let nums: &[u16] = &[211, 281, 421, 461];

// Conversion from &[u8] to &[u16::ULE] is infallible.
let zerovec: ZeroVec<u16> = ZeroVec::try_from_bytes(bytes).expect("infallible");

assert!(matches!(zerovec, ZeroVec::Borrowed(_)));
assert_eq!(zerovec.get(2), Some(421));
assert_eq!(zerovec, nums);

Variants (Non-exhaustive)

Non-exhaustive enums could have additional variants added in future. Therefore, when matching against variants of non-exhaustive enums, an extra wildcard arm must be added to account for any future variants.

Owned(Vec<T::ULE>)

Borrowed(&'a [T::ULE])

Implementations

impl<'a, T: ?Sized> ZeroVec<'a, T> where
    T: AsULE, 

pub fn try_from_bytes(
    bytes: &'a [u8]
) -> Result<Self, <<T as AsULE>::ULE as ULE>::Error>

Parses a &[u8] buffer into a ZeroVec<T>.

This function is infallible for built-in integer types, but fallible for other types, such as char. For more information, see ULE::parse_byte_slice.

The bytes within the byte buffer must remain constant for the life of the ZeroVec.

Endianness

The byte buffer must be encoded in little-endian, even if running in a big-endian environment. This ensures a consistent representation of data across platforms.

Example

use zerovec::ZeroVec;

let bytes: &[u8] = &[0xD3, 0x00, 0x19, 0x01, 0xA5, 0x01, 0xCD, 0x01];
let zerovec: ZeroVec<u16> = ZeroVec::try_from_bytes(bytes).expect("infallible");

assert!(matches!(zerovec, ZeroVec::Borrowed(_)));
assert_eq!(zerovec.get(2), Some(421));

pub fn as_bytes(&self) -> &[u8]

Returns a ZeroVec<T> as its underlying &[u8] byte buffer representation.

Useful for serialization.

Example

use zerovec::ZeroVec;

// The little-endian bytes correspond to the numbers on the following line.
let bytes: &[u8] = &[0xD3, 0x00, 0x19, 0x01, 0xA5, 0x01, 0xCD, 0x01];
let nums: &[u16] = &[211, 281, 421, 461];

let zerovec = ZeroVec::from_aligned(nums);

assert_eq!(bytes, zerovec.as_bytes());

pub fn as_slice(&self) -> &[T::ULE]

Dereferences this ZeroVec<T> as &[T::ULE]. Most other functions on ZeroVec<T> use this function as a building block.

pub fn len(&self) -> usize

Returns the number of elements in this ZeroVec<T>.

Example

use zerovec::ZeroVec;
use zerovec::ule::AsULE;

let bytes: &[u8] = &[0xD3, 0x00, 0x19, 0x01, 0xA5, 0x01, 0xCD, 0x01];
let zerovec: ZeroVec<u16> = ZeroVec::try_from_bytes(bytes).expect("infallible");

assert_eq!(4, zerovec.len());
assert_eq!(
    bytes.len(),
    zerovec.len() * std::mem::size_of::<<u16 as AsULE>::ULE>()
);

pub fn is_empty(&self) -> bool

Returns whether the vec is empty.

Example

use zerovec::ZeroVec;

let bytes: &[u8] = &[0xD3, 0x00, 0x19, 0x01, 0xA5, 0x01, 0xCD, 0x01];
let zerovec: ZeroVec<u16> = ZeroVec::try_from_bytes(bytes).expect("infallible");
assert!(!zerovec.is_empty());

let emptyvec: ZeroVec<u16> = ZeroVec::try_from_bytes(&[]).expect("infallible");
assert!(emptyvec.is_empty());

impl<T> ZeroVec<'_, T> where
    T: AsULE, 

pub fn from_aligned(other: &[T]) -> Self

Creates a ZeroVec<T> from a &[T].

This function allocates memory and results in an Owned instance of ZeroVec<T>.

Example

use zerovec::ZeroVec;

// The little-endian bytes correspond to the numbers on the following line.
let bytes: &[u8] = &[0xD3, 0x00, 0x19, 0x01, 0xA5, 0x01, 0xCD, 0x01];
let nums: &[u16] = &[211, 281, 421, 461];

let zerovec = ZeroVec::from_aligned(nums);

assert!(matches!(zerovec, ZeroVec::Owned(_)));
assert_eq!(bytes, zerovec.as_bytes());

pub fn to_vec(&self) -> Vec<T>

Creates a Vec<T> from a ZeroVec<T>.

Example

use zerovec::ZeroVec;

let nums: &[u16] = &[211, 281, 421, 461];
let vec: Vec<u16> = ZeroVec::from_aligned(nums).to_vec();

assert_eq!(nums, vec.as_slice());

impl<T: ?Sized> ZeroVec<'_, T> where
    T: AsULE + Copy, 

pub fn get(&self, index: usize) -> Option<T>

Gets the element at the specified index. Returns None if out of range.

The element is returned by value, so T must implement Copy.

Example

use zerovec::ZeroVec;

let bytes: &[u8] = &[0xD3, 0x00, 0x19, 0x01, 0xA5, 0x01, 0xCD, 0x01];
let zerovec: ZeroVec<u16> = ZeroVec::try_from_bytes(bytes).expect("infallible");

assert_eq!(zerovec.get(2), Some(421));
assert_eq!(zerovec.get(4), None);

pub fn first(&self) -> Option<T>

Gets the first element. Returns None if empty.

The element is returned by value, so T must implement Copy.

Example

use zerovec::ZeroVec;

let bytes: &[u8] = &[0xD3, 0x00, 0x19, 0x01, 0xA5, 0x01, 0xCD, 0x01];
let zerovec: ZeroVec<u16> = ZeroVec::try_from_bytes(bytes).expect("infallible");

assert_eq!(zerovec.first(), Some(211));

pub fn last(&self) -> Option<T>

Gets the last element. Returns None if empty.

The element is returned by value, so T must implement Copy.

Example

use zerovec::ZeroVec;

let bytes: &[u8] = &[0xD3, 0x00, 0x19, 0x01, 0xA5, 0x01, 0xCD, 0x01];
let zerovec: ZeroVec<u16> = ZeroVec::try_from_bytes(bytes).expect("infallible");

assert_eq!(zerovec.last(), Some(461));

pub fn iter(&self) -> impl Iterator<Item = T> + '_

Gets an iterator over the elements.

The elements are returned by value, so T must implement Copy.

Example

use zerovec::ZeroVec;

let bytes: &[u8] = &[0xD3, 0x00, 0x19, 0x01, 0xA5, 0x01, 0xCD, 0x01];
let zerovec: ZeroVec<u16> = ZeroVec::try_from_bytes(bytes).expect("infallible");
let mut it = zerovec.iter();

assert_eq!(it.next(), Some(211));
assert_eq!(it.next(), Some(281));
assert_eq!(it.next(), Some(421));
assert_eq!(it.next(), Some(461));
assert_eq!(it.next(), None);

pub fn into_owned(self) -> ZeroVec<'static, T>

Converts a borrowed ZeroVec to an owned ZeroVec. No-op if already owned.

Example

use zerovec::ZeroVec;

let bytes: &[u8] = &[0xD3, 0x00, 0x19, 0x01, 0xA5, 0x01, 0xCD, 0x01];
let zerovec: ZeroVec<u16> = ZeroVec::try_from_bytes(bytes).expect("infallible");
assert!(matches!(zerovec, ZeroVec::Borrowed(_)));

let owned = zerovec.into_owned();
assert!(matches!(owned, ZeroVec::Owned(_)));

impl<T> ZeroVec<'_, T> where
    T: AsULE + Ord, 

pub fn binary_search(&self, x: &T) -> Result<usize, usize>

Binary searches a sorted ZeroVec<T> for the given element. For more information, see the primitive function binary_search.

Example

use zerovec::ZeroVec;

let bytes: &[u8] = &[0xD3, 0x00, 0x19, 0x01, 0xA5, 0x01, 0xCD, 0x01];
let zerovec: ZeroVec<u16> = ZeroVec::try_from_bytes(bytes).expect("infallible");

assert_eq!(zerovec.binary_search(&281), Ok(1));
assert_eq!(zerovec.binary_search(&282), Err(2));

Trait Implementations

impl<'a, T: Clone + ?Sized> Clone for ZeroVec<'a, T> where
    T: AsULE,
    T::ULE: Clone,
    T::ULE: Clone, 

fn clone(&self) -> ZeroVec<'a, T>

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl<T> Debug for ZeroVec<'_, T> where
    T: AsULE + Debug, 

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl<T> PartialEq<&'_ [T]> for ZeroVec<'_, T> where
    T: AsULE + Copy + PartialEq, 

fn eq(&self, other: &&[T]) -> bool

This method tests for self and other values to be equal, and is used by ==.

#[must_use]

fn ne(&self, other: &Rhs) -> bool

This method tests for !=.

impl<'a, 'b, T> PartialEq<ZeroVec<'b, T>> for ZeroVec<'a, T> where
    T: AsULE + Copy + PartialEq, 

fn eq(&self, other: &ZeroVec<'b, T>) -> bool

This method tests for self and other values to be equal, and is used by ==.

#[must_use]

fn ne(&self, other: &Rhs) -> bool

This method tests for !=.

impl<'a, T> ZeroVecLike<'a, T> for ZeroVec<'a, T> where
    T: AsULE + Ord + Copy, 

type NeedleType = T

The type received by Self::binary_search()

type GetType = T::ULE

The type returned by Self::get()

fn binary_search(&self, k: &T) -> Result<usize, usize>

Search for a key in a sorted vector, returns Ok(index) if found, returns Err(insert_index) if not found, where insert_index is the index where it should be inserted to maintain sort order.

fn get(&self, index: usize) -> Option<&T::ULE>

Get element at index

fn insert(&mut self, index: usize, value: T)

Insert an element at index

fn remove(&mut self, index: usize) -> T

Remove the element at index (panicking if nonexistant)

fn replace(&mut self, index: usize, value: T) -> T

Replace the element at index with another one, returning the old element

fn push(&mut self, value: T)

Push an element to the end of this vector

fn len(&self) -> usize

The length of this vector

fn new() -> Self

Create a new, empty vector

fn with_capacity(cap: usize) -> Self

Create a new, empty vector, with given capacity

fn clear(&mut self)

Remove all elements from the vector

fn reserve(&mut self, addl: usize)

Reserve space for addl additional elements

fn is_ascending(&self) -> bool

Check if this vector is in ascending order according to Ts Ord impl