Struct ZeroVec 

pub struct ZeroVec<'a, T>
where
    T: AsULE,
{ /* private fields */ }

A zero-copy, byte-aligned 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. For variable-width types like str, see VarZeroVec. zerovec::make_ule may be used to automatically implement AsULE for a type and generate the underlying ULE type.

Typically, the zero-copy equivalent of a Vec<T> will simply be ZeroVec<'a, T>.

Most of the methods on ZeroVec<'a, T> come from its Deref implementation to ZeroSlice<T>.

For creating zero-copy vectors of fixed-size types, see VarZeroVec.

ZeroVec<T> behaves much like Cow, where it can be constructed from owned data (and then mutated!) but can also borrow from some buffer.

Example

use zerovec::ZeroVec;

// The little-endian bytes correspond to the numbers on the following line.
let nums: &[u16] = &[211, 281, 421, 461];

#[derive(serde::Serialize, serde::Deserialize)]
struct Data<'a> {
    #[serde(borrow)]
    nums: ZeroVec<'a, u16>,
}

// The owned version will allocate
let data = Data {
    nums: ZeroVec::alloc_from_slice(nums),
};
let bincode_bytes =
    bincode::serialize(&data).expect("Serialization should be successful");

// Will deserialize without allocations
let deserialized: Data = bincode::deserialize(&bincode_bytes)
    .expect("Deserialization should be successful");

// This deserializes without allocation!
assert!(!deserialized.nums.is_owned());
assert_eq!(deserialized.nums.get(2), Some(421));
assert_eq!(deserialized.nums, nums);

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, with some results found in the crate-level documentation.

See the design doc for more details.

Implementations

impl<'a, T: AsULE> ZeroVec<'a, T>

pub const fn new() -> Self

Creates a new, borrowed, empty ZeroVec<T>.

Examples

use zerovec::ZeroVec;

let zv: ZeroVec<u16> = ZeroVec::new();
assert!(zv.is_empty());

pub const fn const_len(&self) -> usize

Same as ZeroSlice::len, which is available through Deref and not const.

pub const fn new_borrowed(slice: &'a [T::ULE]) -> Self

Creates a new borrowed ZeroVec using an existing backing buffer

✨ Enabled with the alloc Cargo feature.

pub fn parse_bytes(bytes: &'a [u8]) -> Result<Self, UleError>

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_bytes_to_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::parse_bytes(bytes).expect("infallible");

assert!(!zerovec.is_owned());
assert_eq!(zerovec.get(2), Some(421));

pub const unsafe fn from_bytes_unchecked(bytes: &'a [u8]) -> Self

Uses a &[u8] buffer as a ZeroVec<T> without any verification.

Safety

bytes need to be an output from ZeroSlice::as_bytes().

pub const fn as_slice(&self) -> &ZeroSlice<T>

Returns this ZeroVec as a ZeroSlice.

To get a reference with a longer lifetime from a borrowed ZeroVec, use ZeroVec::as_maybe_borrowed.

pub fn is_owned(&self) -> bool

Check if this type is fully owned

pub fn as_maybe_borrowed(&self) -> Option<&'a ZeroSlice<T>>

If this is a borrowed ZeroVec, return it as a slice that covers its lifetime parameter.

To infallibly get a ZeroSlice with a shorter lifetime, use ZeroVec::as_slice.

pub fn owned_capacity(&self) -> Option<NonZeroUsize>

If the ZeroVec is owned, returns the capacity of the vector.

Otherwise, if the ZeroVec is borrowed, returns None.

Examples

use zerovec::ZeroVec;

let mut zv = ZeroVec::<u8>::new_borrowed(&[0, 1, 2, 3]);
assert!(!zv.is_owned());
assert_eq!(zv.owned_capacity(), None);

// Convert to owned without appending anything
zv.with_mut(|v| ());
assert!(zv.is_owned());
assert_eq!(zv.owned_capacity(), Some(4.try_into().unwrap()));

// Double the size by appending
zv.with_mut(|v| v.push(0));
assert!(zv.is_owned());
assert_eq!(zv.owned_capacity(), Some(8.try_into().unwrap()));

impl<'a, T> ZeroVec<'a, T>

where T: EqULE,

pub fn try_from_slice(slice: &'a [T]) -> Option<Self>

Attempts to create a ZeroVec<'a, T> from a &'a [T] by borrowing the argument.

If this is not possible, such as on a big-endian platform, None is returned.

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];

if let Some(zerovec) = ZeroVec::try_from_slice(nums) {
    assert!(!zerovec.is_owned());
    assert_eq!(bytes, zerovec.as_bytes());
}

impl<'a, T> ZeroVec<'a, T>

where T: AsULE,

pub fn clear(&mut self)

Remove all elements from this ZeroVec and reset it to an empty borrowed state.

pub fn truncated(self, max: usize) -> Self

Truncates this vector to min(self.len(), max).

Methods from Deref<Target = ZeroSlice<T>>

pub fn as_zerovec(&self) -> ZeroVec<'_, T>

Get this ZeroSlice as a borrowed ZeroVec

ZeroSlice does not have most of the methods that ZeroVec does, so it is recommended to convert it to a ZeroVec before doing anything.

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

Returns this slice 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, 0x80];
let nums: &[u16] = &[211, 281, 421, 32973];

let zerovec = ZeroVec::alloc_from_slice(nums);

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

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

Dereferences this slice as &[T::ULE].

pub fn len(&self) -> usize

Returns the number of elements in this slice.

Example

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

let bytes: &[u8] = &[0xD3, 0x00, 0x19, 0x01, 0xA5, 0x01, 0xCD, 0x80];
let zerovec: ZeroVec<u16> =
    ZeroVec::parse_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 this slice is empty.

Example

use zerovec::ZeroVec;

let bytes: &[u8] = &[0xD3, 0x00, 0x19, 0x01, 0xA5, 0x01, 0xCD, 0x80];
let zerovec: ZeroVec<u16> =
    ZeroVec::parse_bytes(bytes).expect("infallible");
assert!(!zerovec.is_empty());

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

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

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

Example

use zerovec::ZeroVec;

let bytes: &[u8] = &[0xD3, 0x00, 0x19, 0x01, 0xA5, 0x01, 0xCD, 0x80];
let zerovec: ZeroVec<u16> =
    ZeroVec::parse_bytes(bytes).expect("infallible");

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

pub fn get_as_array<const N: usize>(&self) -> Option<[T; N]>

Gets the entire slice as an array of length N. Returns None if the slice does not have exactly N elements.

Example

use zerovec::ZeroVec;

let bytes: &[u8] = &[0xD3, 0x00, 0x19, 0x01, 0xA5, 0x01, 0xCD, 0x80];
let zerovec: ZeroVec<u16> =
    ZeroVec::parse_bytes(bytes).expect("infallible");
let array: [u16; 4] =
    zerovec.get_as_array().expect("should be 4 items in array");

assert_eq!(array[2], 421);

pub fn get_subslice(&self, range: Range<usize>) -> Option<&ZeroSlice<T>>

Gets a subslice of elements within a certain range. Returns None if the range is out of bounds of this ZeroSlice.

Example

use zerovec::ZeroVec;

let bytes: &[u8] = &[0xD3, 0x00, 0x19, 0x01, 0xA5, 0x01, 0xCD, 0x80];
let zerovec: ZeroVec<u16> =
    ZeroVec::parse_bytes(bytes).expect("infallible");

assert_eq!(
    zerovec.get_subslice(1..3),
    Some(&*ZeroVec::from_slice_or_alloc(&[0x0119, 0x01A5]))
);
assert_eq!(zerovec.get_subslice(3..5), None);

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

Get a borrowed reference to the underlying ULE type at a specified index.

Prefer Self::get() over this method where possible since working directly with ULE types is less ergonomic

pub fn cast<P>(&self) -> &ZeroSlice<P>

where P: AsULE<ULE = T::ULE>,

Casts a ZeroSlice<T> to a compatible ZeroSlice<P>.

T and P are compatible if they have the same ULE representation.

If the ULEs of T and P are different, use Self::try_as_converted().

Examples

use zerovec::ZeroSlice;

const BYTES: &[u8] = &[0xD3, 0x00, 0x19, 0x01, 0xA5, 0x01, 0xCD, 0x80];
const ZS_U16: &ZeroSlice<u16> = {
    match ZeroSlice::<u16>::try_from_bytes(BYTES) {
        Ok(s) => s,
        Err(_) => unreachable!(),
    }
};

let zs_i16: &ZeroSlice<i16> = ZS_U16.cast();

assert_eq!(ZS_U16.get(3), Some(32973));
assert_eq!(zs_i16.get(3), Some(-32563));

pub fn try_as_converted<P: AsULE>(&self) -> Result<&ZeroSlice<P>, UleError>

Converts a &ZeroSlice<T> into a &ZeroSlice<P>.

The resulting slice will have the same length as the original slice if and only if T::ULE and P::ULE are the same size.

If T and P have the exact same ULE, use Self::cast().

Examples

use zerovec::ZeroSlice;

const BYTES: &[u8] = &[0x7F, 0xF3, 0x01, 0x00, 0x49, 0xF6, 0x01, 0x00];
const ZS_U32: &ZeroSlice<u32> = {
    match ZeroSlice::<u32>::try_from_bytes(BYTES) {
        Ok(s) => s,
        Err(_) => unreachable!(),
    }
};

let zs_u8_4: &ZeroSlice<[u8; 4]> =
    ZS_U32.try_as_converted().expect("valid code points");

assert_eq!(ZS_U32.get(0), Some(127871));
assert_eq!(zs_u8_4.get(0), Some([0x7F, 0xF3, 0x01, 0x00]));

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

Gets the first element. Returns None if empty.

Example

use zerovec::ZeroVec;

let bytes: &[u8] = &[0xD3, 0x00, 0x19, 0x01, 0xA5, 0x01, 0xCD, 0x80];
let zerovec: ZeroVec<u16> =
    ZeroVec::parse_bytes(bytes).expect("infallible");

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

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

Gets the last element. Returns None if empty.

Example

use zerovec::ZeroVec;

let bytes: &[u8] = &[0xD3, 0x00, 0x19, 0x01, 0xA5, 0x01, 0xCD, 0x80];
let zerovec: ZeroVec<u16> =
    ZeroVec::parse_bytes(bytes).expect("infallible");

assert_eq!(zerovec.last(), Some(32973));

pub fn iter<'a>(&'a self) -> ZeroSliceIter<'a, T>

Gets an iterator over the elements.

Example

use zerovec::ZeroVec;

let bytes: &[u8] = &[0xD3, 0x00, 0x19, 0x01, 0xA5, 0x01, 0xCD, 0x80];
let zerovec: ZeroVec<u16> =
    ZeroVec::parse_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(32973));
assert_eq!(it.next(), None);

pub fn split_first(&self) -> Option<(T, &ZeroSlice<T>)>

Returns a tuple with the first element and a subslice of the remaining elements.

Example

use zerovec::ule::AsULE;
use zerovec::ZeroSlice;

const DATA: &ZeroSlice<u16> =
    ZeroSlice::<u16>::from_ule_slice(&<u16 as AsULE>::ULE::from_array([
        211, 281, 421, 32973,
    ]));
const EXPECTED_VALUE: (u16, &ZeroSlice<u16>) = (
    211,
    ZeroSlice::<u16>::from_ule_slice(&<u16 as AsULE>::ULE::from_array([
        281, 421, 32973,
    ])),
);
assert_eq!(EXPECTED_VALUE, DATA.split_first().unwrap());

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, 0x80];
let zerovec: ZeroVec<u16> =
    ZeroVec::parse_bytes(bytes).expect("infallible");

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

pub fn binary_search_by( &self, predicate: impl FnMut(T) -> Ordering, ) -> Result<usize, usize>

Binary searches a sorted ZeroVec<T> based on a given predicate. For more information, see the primitive function binary_search_by.

Example

use zerovec::ZeroVec;

let bytes: &[u8] = &[0xD3, 0x00, 0x19, 0x01, 0xA5, 0x01, 0xCD, 0x80];
let zerovec: ZeroVec<u16> =
    ZeroVec::parse_bytes(bytes).expect("infallible");

assert_eq!(zerovec.binary_search_by(|x| x.cmp(&281)), Ok(1));
assert_eq!(zerovec.binary_search_by(|x| x.cmp(&282)), Err(2));

Trait Implementations

impl<'a, T: AsULE> AsRef<[<T as AsULE>::ULE]> for ZeroVec<'a, T>

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

Converts this type into a shared reference of the (usually inferred) input type.

impl<'a, T: AsULE> AsRef<ZeroSlice<T>> for ZeroVec<'a, T>

fn as_ref(&self) -> &ZeroSlice<T>

Converts this type into a shared reference of the (usually inferred) input type.

impl<'a, T: AsULE> Clone for ZeroVec<'a, T>

fn clone(&self) -> Self

Returns a duplicate 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<'a, T: AsULE> Default for ZeroVec<'a, T>

fn default() -> Self

Returns the “default value” for a type.

impl<'a, T: AsULE> Deref for ZeroVec<'a, T>

type Target = ZeroSlice<T>

The resulting type after dereferencing.

fn deref(&self) -> &Self::Target

Dereferences the value.

impl<T> EncodeAsVarULE<ZeroSlice<T>> for ZeroVec<'_, T>

where T: AsULE + 'static,

fn encode_var_ule_as_slices<R>(&self, _: impl FnOnce(&[&[u8]]) -> R) -> R

Calls cb with a piecewise list of byte slices that when concatenated produce the memory pattern of the corresponding instance of T.

fn encode_var_ule_len(&self) -> usize

Return the length, in bytes, of the corresponding VarULE type

fn encode_var_ule_write(&self, dst: &mut [u8])

Write the corresponding VarULE type to the dst buffer. dst should be the size of Self::encode_var_ule_len()

impl<'a, T: AsULE> From<&'a [<T as AsULE>::ULE]> for ZeroVec<'a, T>

fn from(other: &'a [T::ULE]) -> Self

Converts to this type from the input type.

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

fn cmp(&self, other: &Self) -> Ordering

This method returns an Ordering between self and other.

fn max(self, other: Self) -> Self

where Self: Sized,

Compares and returns the maximum of two values.

fn min(self, other: Self) -> Self

where Self: Sized,

Compares and returns the minimum of two values.

fn clamp(self, min: Self, max: Self) -> Self

where Self: Sized,

Restrict a value to a certain interval.

impl<T> PartialEq<&[T]> for ZeroVec<'_, T>

where T: AsULE + PartialEq,

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

Tests for self and other values to be equal, and is used by ==.

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

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl<T, const N: usize> PartialEq<[T; N]> for ZeroVec<'_, T>

where T: AsULE + PartialEq,

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

Tests for self and other values to be equal, and is used by ==.

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

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl<'a, T> PartialEq<ZeroSlice<T>> for ZeroVec<'a, T>

where T: AsULE + PartialEq,

fn eq(&self, other: &ZeroSlice<T>) -> bool

Tests for self and other values to be equal, and is used by ==.

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

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl<'a, T> PartialEq<ZeroVec<'a, T>> for ZeroSlice<T>

where T: AsULE + PartialEq,

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

Tests for self and other values to be equal, and is used by ==.

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

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl<'a, 'b, T> PartialEq<ZeroVec<'b, T>> for ZeroVec<'a, T>

where T: AsULE + PartialEq,

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

Tests for self and other values to be equal, and is used by ==.

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

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl<'a, T: AsULE + PartialOrd> PartialOrd for ZeroVec<'a, T>

fn partial_cmp(&self, other: &Self) -> Option<Ordering>

This method returns an ordering between self and other values if one exists.

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

Tests less than (for self and other) and is used by the < operator.

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

Tests less than or equal to (for self and other) and is used by the <= operator.

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

Tests greater than (for self and other) and is used by the > operator.

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

Tests greater than or equal to (for self and other) and is used by the >= operator.

impl<'a, T: 'static + AsULE> Yokeable<'a> for ZeroVec<'static, T>

This impl requires enabling the optional yoke Cargo feature of the zerovec crate

type Output = ZeroVec<'a, T>

This type MUST be Self with the 'static replaced with 'a, i.e. Self<'a>

fn transform(&'a self) -> &'a Self::Output

This method must cast self between &'a Self<'static> and &'a Self<'a>.

fn transform_owned(self) -> Self::Output

This method must cast self between Self<'static> and Self<'a>.

unsafe fn make(from: Self::Output) -> Self

This method can be used to cast away Self<'a>’s lifetime.

fn transform_mut<F>(&'a mut self, f: F)

where F: 'static + for<'b> FnOnce(&'b mut Self::Output),

This method must cast self between &'a mut Self<'static> and &'a mut Self<'a>, and pass it to f.

impl<'zf, T> ZeroFrom<'zf, ZeroSlice<T>> for ZeroVec<'zf, T>

where T: 'static + AsULE,

fn zero_from(other: &'zf ZeroSlice<T>) -> Self

Clone the other C into a struct that may retain references into C.

impl<'zf, T> ZeroFrom<'zf, ZeroVec<'_, T>> for ZeroVec<'zf, T>

where T: 'static + AsULE,

fn zero_from(other: &'zf ZeroVec<'_, T>) -> Self

Clone the other C into a struct that may retain references into C.

impl<T> Eq for ZeroVec<'_, T>

where T: AsULE + Eq,

impl<'a, T: AsULE> Send for ZeroVec<'a, T>

where T::ULE: Send + Sync,

impl<'a, T: AsULE> Sync for ZeroVec<'a, T>

where T::ULE: Sync,