/rust/registry/src/index.crates.io-1949cf8c6b5b557f/zerovec-0.11.4/src/varzerovec/vec.rs

Source
// This file is part of ICU4X. For terms of use, please see the file
// called LICENSE at the top level of the ICU4X source tree
// (online at: https://github.com/unicode-org/icu4x/blob/main/LICENSE ).

use crate::ule::*;

use core::cmp::{Ord, Ordering, PartialOrd};
use core::fmt;
use core::ops::Deref;

use super::*;

/// A zero-copy, byte-aligned vector for variable-width types.
///
/// `VarZeroVec<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, and
/// where `T`'s data is variable-length (e.g. `String`)
///
/// `T` must implement [`VarULE`], which is already implemented for [`str`] and `[u8]`. For storing more
/// complicated series of elements, it is implemented on `ZeroSlice<T>` as well as `VarZeroSlice<T>`
/// for nesting. [`zerovec::make_varule`](crate::make_varule) may be used to generate
/// a dynamically-sized [`VarULE`] type and conversions to and from a custom type.
///
/// For example, here are some owned types and their zero-copy equivalents:
///
/// - `Vec<String>`: `VarZeroVec<'a, str>`
/// - `Vec<Vec<u8>>>`: `VarZeroVec<'a, [u8]>`
/// - `Vec<Vec<u32>>`: `VarZeroVec<'a, ZeroSlice<u32>>`
/// - `Vec<Vec<String>>`: `VarZeroVec<'a, VarZeroSlice<str>>`
///
/// Most of the methods on `VarZeroVec<'a, T>` come from its [`Deref`] implementation to [`VarZeroSlice<T>`](VarZeroSlice).
///
/// For creating zero-copy vectors of fixed-size types, see [`ZeroVec`](crate::ZeroVec).
///
/// `VarZeroVec<T>` behaves much like [`Cow`](alloc::borrow::Cow), where it can be constructed from
/// owned data (and then mutated!) but can also borrow from some buffer.
///
/// The `F` type parameter is a [`VarZeroVecFormat`] (see its docs for more details), which can be used to select the
/// precise format of the backing buffer with various size and performance tradeoffs. It defaults to [`Index16`].
///
/// # Bytes and Equality
///
/// Two [`VarZeroVec`]s are equal if and only if their bytes are equal, as described in the trait
/// [`VarULE`]. However, we do not guarantee stability of byte equality or serialization format
/// across major SemVer releases.
///
/// To compare a [`Vec<T>`] to a [`VarZeroVec<T>`], it is generally recommended to use
/// [`Iterator::eq`], since it is somewhat expensive at runtime to convert from a [`Vec<T>`] to a
/// [`VarZeroVec<T>`] or vice-versa.
///
/// Prior to zerovec reaching 1.0, the precise byte representation of [`VarZeroVec`] is still
/// under consideration, with different options along the space-time spectrum. See
/// [#1410](https://github.com/unicode-org/icu4x/issues/1410).
///
/// # Example
///
/// ```rust
/// use zerovec::VarZeroVec;
///
/// // The little-endian bytes correspond to the list of strings.
/// let strings = vec!["w", "ω", "文", "𑄃"];
///
/// #[derive(serde::Serialize, serde::Deserialize)]
/// struct Data<'a> {
///     #[serde(borrow)]
///     strings: VarZeroVec<'a, str>,
/// }
///
/// let data = Data {
///     strings: VarZeroVec::from(&strings),
/// };
///
/// 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");
///
/// assert_eq!(deserialized.strings.get(2), Some("文"));
/// assert_eq!(deserialized.strings, &*strings);
/// ```
///
/// Here's another example with `ZeroSlice<T>` (similar to `[T]`):
///
/// ```rust
/// use zerovec::VarZeroVec;
/// use zerovec::ZeroSlice;
///
/// // The structured list correspond to the list of integers.
/// let numbers: &[&[u32]] = &[
///     &[12, 25, 38],
///     &[39179, 100],
///     &[42, 55555],
///     &[12345, 54321, 9],
/// ];
///
/// #[derive(serde::Serialize, serde::Deserialize)]
/// struct Data<'a> {
///     #[serde(borrow)]
///     vecs: VarZeroVec<'a, ZeroSlice<u32>>,
/// }
///
/// let data = Data {
///     vecs: VarZeroVec::from(numbers),
/// };
///
/// let bincode_bytes =
///     bincode::serialize(&data).expect("Serialization should be successful");
///
/// let deserialized: Data = bincode::deserialize(&bincode_bytes)
///     .expect("Deserialization should be successful");
///
/// assert_eq!(deserialized.vecs[0].get(1).unwrap(), 25);
/// assert_eq!(deserialized.vecs[1], *numbers[1]);
/// ```
///
/// [`VarZeroVec`]s can be nested infinitely via a similar mechanism, see the docs of [`VarZeroSlice`]
/// for more information.
///
/// # How it Works
///
/// `VarZeroVec<T>`, when used with non-human-readable serializers (like `bincode`), will
/// serialize to a specially formatted list of bytes. The format is:
///
/// -  2 bytes for `length` (interpreted as a little-endian u16)
/// - `2 * (length - 1)` bytes of `indices` (interpreted as little-endian u16s)
/// - Remaining bytes for actual `data`
///
/// The format is tweakable by setting the `F` parameter, by default it uses u16 indices and lengths but other
/// `VarZeroVecFormat` types can set other sizes.
///
/// Each element in the `indices` array points to the ending index of its corresponding
/// data part in the `data` list. The starting index can be calculated from the ending index
/// of the next element (or 0 for the first element). The last ending index, not stored in the array, is
/// the length of the `data` segment.
///
/// See [the design doc](https://github.com/unicode-org/icu4x/blob/main/utils/zerovec/design_doc.md) for more details.
///
/// [`ule`]: crate::ule
pub struct VarZeroVec<'a, T: ?Sized, F = Index16>(pub(crate) VarZeroVecInner<'a, T, F>);

pub(crate) enum VarZeroVecInner<'a, T: ?Sized, F = Index16> {
    #[cfg(feature = "alloc")]
    Owned(VarZeroVecOwned<T, F>),
    Borrowed(&'a VarZeroSlice<T, F>),
}

impl<'a, T: ?Sized, F> Clone for VarZeroVec<'a, T, F> {
    fn clone(&self) -> Self {
        match self.0 {
            #[cfg(feature = "alloc")]
            VarZeroVecInner::Owned(ref o) => o.clone().into(),
            VarZeroVecInner::Borrowed(b) => b.into(),
        }
    }
}

impl<T: VarULE + ?Sized, F: VarZeroVecFormat> fmt::Debug for VarZeroVec<'_, T, F>
where
    T: fmt::Debug,
{
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        VarZeroSlice::fmt(self, f)
    }
}

#[cfg(feature = "alloc")]
impl<'a, T: ?Sized, F> From<VarZeroVecOwned<T, F>> for VarZeroVec<'a, T, F> {
    #[inline]
    fn from(other: VarZeroVecOwned<T, F>) -> Self {
        Self(VarZeroVecInner::Owned(other))
    }
}

impl<'a, T: ?Sized, F> From<&'a VarZeroSlice<T, F>> for VarZeroVec<'a, T, F> {
    fn from(other: &'a VarZeroSlice<T, F>) -> Self {
        Self(VarZeroVecInner::Borrowed(other))
    }
}

#[cfg(feature = "alloc")]
impl<'a, T: ?Sized + VarULE, F: VarZeroVecFormat> From<VarZeroVec<'a, T, F>>
    for VarZeroVecOwned<T, F>
{
    #[inline]
    fn from(other: VarZeroVec<'a, T, F>) -> Self {
        match other.0 {
            VarZeroVecInner::Owned(o) => o,
            VarZeroVecInner::Borrowed(b) => b.into(),
        }
    }
}

impl<T: VarULE + ?Sized, F: VarZeroVecFormat> Default for VarZeroVec<'_, T, F> {
    #[inline]
    fn default() -> Self {
        Self::new()
    }
}

impl<T: VarULE + ?Sized, F: VarZeroVecFormat> Deref for VarZeroVec<'_, T, F> {
    type Target = VarZeroSlice<T, F>;
    fn deref(&self) -> &VarZeroSlice<T, F> {
        self.as_slice()
    }
}

impl<'a, T: VarULE + ?Sized, F: VarZeroVecFormat> VarZeroVec<'a, T, F> {
    /// Creates a new, empty `VarZeroVec<T>`.
    ///
    /// # Examples
    ///
    /// ```
    /// use zerovec::VarZeroVec;
    ///
    /// let vzv: VarZeroVec<str> = VarZeroVec::new();
    /// assert!(vzv.is_empty());
    /// ```
    #[inline]
    pub const fn new() -> Self {
        Self(VarZeroVecInner::Borrowed(VarZeroSlice::new_empty()))
    }

    /// Parse a VarZeroVec from a slice of the appropriate format
    ///
    /// Slices of the right format can be obtained via [`VarZeroSlice::as_bytes()`].
    ///
    /// # Example
    ///
    /// ```rust
    /// # use zerovec::VarZeroVec;
    ///
    /// let strings = vec!["foo", "bar", "baz", "quux"];
    /// let vec = VarZeroVec::<str>::from(&strings);
    ///
    /// assert_eq!(&vec[0], "foo");
    /// assert_eq!(&vec[1], "bar");
    /// assert_eq!(&vec[2], "baz");
    /// assert_eq!(&vec[3], "quux");
    /// ```
    pub fn parse_bytes(slice: &'a [u8]) -> Result<Self, UleError> {
        let borrowed = VarZeroSlice::<T, F>::parse_bytes(slice)?;

        Ok(Self(VarZeroVecInner::Borrowed(borrowed)))
    }

    /// Uses a `&[u8]` buffer as a `VarZeroVec<T>` without any verification.
    ///
    /// # Safety
    ///
    /// `bytes` need to be an output from [`VarZeroSlice::as_bytes()`].
    pub const unsafe fn from_bytes_unchecked(bytes: &'a [u8]) -> Self {
        Self(VarZeroVecInner::Borrowed(core::mem::transmute::<
            &[u8],
            &VarZeroSlice<T, F>,
        >(bytes)))
    }

    /// Convert this into a mutable vector of the owned `T` type, cloning if necessary.
    ///
    ///
    /// # Example
    ///
    /// ```rust,ignore
    /// # use zerovec::VarZeroVec;
    /// let strings = vec!["foo", "bar", "baz", "quux"];
    /// let mut vec = VarZeroVec::<str>::from(&strings);
    ///
    /// assert_eq!(vec.len(), 4);
    /// let mutvec = vec.make_mut();
    /// mutvec.push("lorem ipsum".into());
    /// mutvec[2] = "dolor sit".into();
    /// assert_eq!(&vec[0], "foo");
    /// assert_eq!(&vec[1], "bar");
    /// assert_eq!(&vec[2], "dolor sit");
    /// assert_eq!(&vec[3], "quux");
    /// assert_eq!(&vec[4], "lorem ipsum");
    /// ```
    //
    // This function is crate-public for now since we don't yet want to stabilize
    // the internal implementation details
    #[cfg(feature = "alloc")]
    pub fn make_mut(&mut self) -> &mut VarZeroVecOwned<T, F> {
        match self.0 {
            VarZeroVecInner::Owned(ref mut vec) => vec,
            VarZeroVecInner::Borrowed(slice) => {
                let new_self = VarZeroVecOwned::from_slice(slice);
                *self = new_self.into();
                // recursion is limited since we are guaranteed to hit the Owned branch
                self.make_mut()
            }
        }
    }

    /// Converts a borrowed ZeroVec to an owned ZeroVec. No-op if already owned.
    ///
    /// # Example
    ///
    /// ```
    /// # use zerovec::VarZeroVec;
    ///
    /// let strings = vec!["foo", "bar", "baz", "quux"];
    /// let vec = VarZeroVec::<str>::from(&strings);
    ///
    /// assert_eq!(vec.len(), 4);
    /// // has 'static lifetime
    /// let owned = vec.into_owned();
    /// ```
    #[cfg(feature = "alloc")]
    pub fn into_owned(mut self) -> VarZeroVec<'static, T, F> {
        self.make_mut();
        match self.0 {
            VarZeroVecInner::Owned(vec) => vec.into(),
            _ => unreachable!(),
        }
    }

    /// Obtain this `VarZeroVec` as a [`VarZeroSlice`]
    pub fn as_slice(&self) -> &VarZeroSlice<T, F> {
        match self.0 {
            #[cfg(feature = "alloc")]
            VarZeroVecInner::Owned(ref owned) => owned,
            VarZeroVecInner::Borrowed(b) => b,
        }
    }

    /// Takes the byte vector representing the encoded data of this VarZeroVec. If borrowed,
    /// this function allocates a byte vector and copies the borrowed bytes into it.
    ///
    /// The bytes can be passed back to [`Self::parse_bytes()`].
    ///
    /// To get a reference to the bytes without moving, see [`VarZeroSlice::as_bytes()`].
    ///
    /// # Example
    ///
    /// ```rust
    /// # use zerovec::VarZeroVec;
    ///
    /// let strings = vec!["foo", "bar", "baz"];
    /// let bytes = VarZeroVec::<str>::from(&strings).into_bytes();
    ///
    /// let mut borrowed: VarZeroVec<str> =
    ///     VarZeroVec::parse_bytes(&bytes).unwrap();
    /// assert_eq!(borrowed, &*strings);
    /// ```
    #[cfg(feature = "alloc")]
    pub fn into_bytes(self) -> alloc::vec::Vec<u8> {
        match self.0 {
            #[cfg(feature = "alloc")]
            VarZeroVecInner::Owned(vec) => vec.into_bytes(),
            VarZeroVecInner::Borrowed(vec) => vec.as_bytes().to_vec(),
        }
    }

    /// Return whether the [`VarZeroVec`] is operating on owned or borrowed
    /// data. [`VarZeroVec::into_owned()`] and [`VarZeroVec::make_mut()`] can
    /// be used to force it into an owned type
    pub fn is_owned(&self) -> bool {
        match self.0 {
            #[cfg(feature = "alloc")]
            VarZeroVecInner::Owned(..) => true,
            VarZeroVecInner::Borrowed(..) => false,
        }
    }

    #[doc(hidden)]
    pub fn as_components<'b>(&'b self) -> VarZeroVecComponents<'b, T, F> {
        self.as_slice().as_components()
    }
}

#[cfg(feature = "alloc")]
impl<A, T, F> From<&alloc::vec::Vec<A>> for VarZeroVec<'static, T, F>
where
    T: VarULE + ?Sized,
    A: EncodeAsVarULE<T>,
    F: VarZeroVecFormat,
{
    #[inline]
    fn from(elements: &alloc::vec::Vec<A>) -> Self {
        Self::from(elements.as_slice())
    }
}

#[cfg(feature = "alloc")]
impl<A, T, F> From<&[A]> for VarZeroVec<'static, T, F>
where
    T: VarULE + ?Sized,
    A: EncodeAsVarULE<T>,
    F: VarZeroVecFormat,
{
    #[inline]
    fn from(elements: &[A]) -> Self {
        if elements.is_empty() {
            VarZeroSlice::new_empty().into()
        } else {
            #[expect(clippy::unwrap_used)] // TODO(#1410) Better story for fallibility
            VarZeroVecOwned::try_from_elements(elements).unwrap().into()
        }
    }
}

#[cfg(feature = "alloc")]
impl<A, T, F, const N: usize> From<&[A; N]> for VarZeroVec<'static, T, F>
where
    T: VarULE + ?Sized,
    A: EncodeAsVarULE<T>,
    F: VarZeroVecFormat,
{
    #[inline]
    fn from(elements: &[A; N]) -> Self {
        Self::from(elements.as_slice())
    }
}

impl<'a, 'b, T, F> PartialEq<VarZeroVec<'b, T, F>> for VarZeroVec<'a, T, F>
where
    T: VarULE,
    T: ?Sized,
    T: PartialEq,
    F: VarZeroVecFormat,
{
    #[inline]
    fn eq(&self, other: &VarZeroVec<'b, T, F>) -> bool {
        // VZV::from_elements used to produce a non-canonical representation of the
        // empty VZV, so we cannot use byte equality for empty vecs.
        if self.is_empty() || other.is_empty() {
            return self.is_empty() && other.is_empty();
        }
        // VarULE has an API guarantee that byte equality is semantic equality.
        // For non-empty VZVs, there's only a single metadata representation,
        // so this guarantee extends to the whole VZV representation.
        self.as_bytes().eq(other.as_bytes())
    }
}

impl<'a, T, F> Eq for VarZeroVec<'a, T, F>
where
    T: VarULE,
    T: ?Sized,
    T: Eq,
    F: VarZeroVecFormat,
{
}

impl<T, A, F> PartialEq<&'_ [A]> for VarZeroVec<'_, T, F>
where
    T: VarULE + ?Sized,
    T: PartialEq,
    A: AsRef<T>,
    F: VarZeroVecFormat,
{
    #[inline]
    fn eq(&self, other: &&[A]) -> bool {
        self.iter().eq(other.iter().map(|t| t.as_ref()))
    }
}

impl<T, A, F, const N: usize> PartialEq<[A; N]> for VarZeroVec<'_, T, F>
where
    T: VarULE + ?Sized,
    T: PartialEq,
    A: AsRef<T>,
    F: VarZeroVecFormat,
{
    #[inline]
    fn eq(&self, other: &[A; N]) -> bool {
        self.iter().eq(other.iter().map(|t| t.as_ref()))
    }
}

impl<'a, T: VarULE + ?Sized + PartialOrd, F: VarZeroVecFormat> PartialOrd for VarZeroVec<'a, T, F> {
    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
        self.iter().partial_cmp(other.iter())
    }
}

impl<'a, T: VarULE + ?Sized + Ord, F: VarZeroVecFormat> Ord for VarZeroVec<'a, T, F> {
    fn cmp(&self, other: &Self) -> Ordering {
        self.iter().cmp(other.iter())
    }
}

#[test]
fn assert_single_empty_representation() {
    assert_eq!(
        VarZeroVec::<str>::new().as_bytes(),
        VarZeroVec::<str>::from(&[] as &[&str]).as_bytes()
    );

    use crate::map::MutableZeroVecLike;
    let mut vzv = VarZeroVec::<str>::from(&["hello", "world"][..]);
    assert_eq!(vzv.len(), 2);
    assert!(!vzv.as_bytes().is_empty());
    vzv.zvl_remove(0);
    assert_eq!(vzv.len(), 1);
    assert!(!vzv.as_bytes().is_empty());
    vzv.zvl_remove(0);
    assert_eq!(vzv.len(), 0);
    assert!(vzv.as_bytes().is_empty());
    vzv.zvl_insert(0, "something");
    assert_eq!(vzv.len(), 1);
    assert!(!vzv.as_bytes().is_empty());
}

#[test]
fn weird_empty_representation_equality() {
    assert_eq!(
        VarZeroVec::<str>::parse_bytes(&[0, 0, 0, 0]).unwrap(),
        VarZeroVec::<str>::parse_bytes(&[]).unwrap()
    );
}

Coverage Report

Created: 2025-10-13 06:09

Line	Count	Source
1		// This file is part of ICU4X. For terms of use, please see the file
2		// called LICENSE at the top level of the ICU4X source tree
3		// (online at: https://github.com/unicode-org/icu4x/blob/main/LICENSE ).
4
5		use crate::ule::*;
6
7		use core::cmp::{Ord, Ordering, PartialOrd};
8		use core::fmt;
9		use core::ops::Deref;
10
11		use super::*;
12
13		/// A zero-copy, byte-aligned vector for variable-width types.
14		///
15		/// `VarZeroVec<T>` is designed as a drop-in replacement for `Vec<T>` in situations where it is
16		/// desirable to borrow data from an unaligned byte slice, such as zero-copy deserialization, and
17		/// where `T`'s data is variable-length (e.g. `String`)
18		///
19		/// `T` must implement [`VarULE`], which is already implemented for [`str`] and `[u8]`. For storing more
20		/// complicated series of elements, it is implemented on `ZeroSlice<T>` as well as `VarZeroSlice<T>`
21		/// for nesting. [`zerovec::make_varule`](crate::make_varule) may be used to generate
22		/// a dynamically-sized [`VarULE`] type and conversions to and from a custom type.
23		///
24		/// For example, here are some owned types and their zero-copy equivalents:
25		///
26		/// - `Vec<String>`: `VarZeroVec<'a, str>`
27		/// - `Vec<Vec<u8>>>`: `VarZeroVec<'a, [u8]>`
28		/// - `Vec<Vec<u32>>`: `VarZeroVec<'a, ZeroSlice<u32>>`
29		/// - `Vec<Vec<String>>`: `VarZeroVec<'a, VarZeroSlice<str>>`
30		///
31		/// Most of the methods on `VarZeroVec<'a, T>` come from its [`Deref`] implementation to [`VarZeroSlice<T>`](VarZeroSlice).
32		///
33		/// For creating zero-copy vectors of fixed-size types, see [`ZeroVec`](crate::ZeroVec).
34		///
35		/// `VarZeroVec<T>` behaves much like [`Cow`](alloc::borrow::Cow), where it can be constructed from
36		/// owned data (and then mutated!) but can also borrow from some buffer.
37		///
38		/// The `F` type parameter is a [`VarZeroVecFormat`] (see its docs for more details), which can be used to select the
39		/// precise format of the backing buffer with various size and performance tradeoffs. It defaults to [`Index16`].
40		///
41		/// # Bytes and Equality
42		///
43		/// Two [`VarZeroVec`]s are equal if and only if their bytes are equal, as described in the trait
44		/// [`VarULE`]. However, we do not guarantee stability of byte equality or serialization format
45		/// across major SemVer releases.
46		///
47		/// To compare a [`Vec<T>`] to a [`VarZeroVec<T>`], it is generally recommended to use
48		/// [`Iterator::eq`], since it is somewhat expensive at runtime to convert from a [`Vec<T>`] to a
49		/// [`VarZeroVec<T>`] or vice-versa.
50		///
51		/// Prior to zerovec reaching 1.0, the precise byte representation of [`VarZeroVec`] is still
52		/// under consideration, with different options along the space-time spectrum. See
53		/// [#1410](https://github.com/unicode-org/icu4x/issues/1410).
54		///
55		/// # Example
56		///
57		/// ```rust
58		/// use zerovec::VarZeroVec;
59		///
60		/// // The little-endian bytes correspond to the list of strings.
61		/// let strings = vec!["w", "ω", "文", "𑄃"];
62		///
63		/// #[derive(serde::Serialize, serde::Deserialize)]
64		/// struct Data<'a> {
65		/// #[serde(borrow)]
66		/// strings: VarZeroVec<'a, str>,
67		/// }
68		///
69		/// let data = Data {
70		/// strings: VarZeroVec::from(&strings),
71		/// };
72		///
73		/// let bincode_bytes =
74		/// bincode::serialize(&data).expect("Serialization should be successful");
75		///
76		/// // Will deserialize without allocations
77		/// let deserialized: Data = bincode::deserialize(&bincode_bytes)
78		/// .expect("Deserialization should be successful");
79		///
80		/// assert_eq!(deserialized.strings.get(2), Some("文"));
81		/// assert_eq!(deserialized.strings, &*strings);
82		/// ```
83		///
84		/// Here's another example with `ZeroSlice<T>` (similar to `[T]`):
85		///
86		/// ```rust
87		/// use zerovec::VarZeroVec;
88		/// use zerovec::ZeroSlice;
89		///
90		/// // The structured list correspond to the list of integers.
91		/// let numbers: &[&[u32]] = &[
92		/// &[12, 25, 38],
93		/// &[39179, 100],
94		/// &[42, 55555],
95		/// &[12345, 54321, 9],
96		/// ];
97		///
98		/// #[derive(serde::Serialize, serde::Deserialize)]
99		/// struct Data<'a> {
100		/// #[serde(borrow)]
101		/// vecs: VarZeroVec<'a, ZeroSlice<u32>>,
102		/// }
103		///
104		/// let data = Data {
105		/// vecs: VarZeroVec::from(numbers),
106		/// };
107		///
108		/// let bincode_bytes =
109		/// bincode::serialize(&data).expect("Serialization should be successful");
110		///
111		/// let deserialized: Data = bincode::deserialize(&bincode_bytes)
112		/// .expect("Deserialization should be successful");
113		///
114		/// assert_eq!(deserialized.vecs[0].get(1).unwrap(), 25);
115		/// assert_eq!(deserialized.vecs[1], *numbers[1]);
116		/// ```
117		///
118		/// [`VarZeroVec`]s can be nested infinitely via a similar mechanism, see the docs of [`VarZeroSlice`]
119		/// for more information.
120		///
121		/// # How it Works
122		///
123		/// `VarZeroVec<T>`, when used with non-human-readable serializers (like `bincode`), will
124		/// serialize to a specially formatted list of bytes. The format is:
125		///
126		/// - 2 bytes for `length` (interpreted as a little-endian u16)
127		/// - `2 * (length - 1)` bytes of `indices` (interpreted as little-endian u16s)
128		/// - Remaining bytes for actual `data`
129		///
130		/// The format is tweakable by setting the `F` parameter, by default it uses u16 indices and lengths but other
131		/// `VarZeroVecFormat` types can set other sizes.
132		///
133		/// Each element in the `indices` array points to the ending index of its corresponding
134		/// data part in the `data` list. The starting index can be calculated from the ending index
135		/// of the next element (or 0 for the first element). The last ending index, not stored in the array, is
136		/// the length of the `data` segment.
137		///
138		/// See [the design doc](https://github.com/unicode-org/icu4x/blob/main/utils/zerovec/design_doc.md) for more details.
139		///
140		/// [`ule`]: crate::ule
141		pub struct VarZeroVec<'a, T: ?Sized, F = Index16>(pub(crate) VarZeroVecInner<'a, T, F>);
142
143		pub(crate) enum VarZeroVecInner<'a, T: ?Sized, F = Index16> {
144		#[cfg(feature = "alloc")]
145		Owned(VarZeroVecOwned<T, F>),
146		Borrowed(&'a VarZeroSlice<T, F>),
147		}
148
149		impl<'a, T: ?Sized, F> Clone for VarZeroVec<'a, T, F> {
150	0	fn clone(&self) -> Self {
151	0	match self.0 {
152		#[cfg(feature = "alloc")]
153	0	VarZeroVecInner::Owned(ref o) => o.clone().into(),
154	0	VarZeroVecInner::Borrowed(b) => b.into(),
155		}
156	0	}
157		}
158
159		impl<T: VarULE + ?Sized, F: VarZeroVecFormat> fmt::Debug for VarZeroVec<'_, T, F>
160		where
161		T: fmt::Debug,
162		{
163	0	fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
164	0	VarZeroSlice::fmt(self, f)
165	0	} Unexecuted instantiation: <zerovec::varzerovec::vec::VarZeroVec<str> as core::fmt::Debug>::fmt Unexecuted instantiation: <zerovec::varzerovec::vec::VarZeroVec<_, _> as core::fmt::Debug>::fmt
166		}
167
168		#[cfg(feature = "alloc")]
169		impl<'a, T: ?Sized, F> From<VarZeroVecOwned<T, F>> for VarZeroVec<'a, T, F> {
170		#[inline]
171	0	fn from(other: VarZeroVecOwned<T, F>) -> Self {
172	0	Self(VarZeroVecInner::Owned(other))
173	0	}
174		}
175
176		impl<'a, T: ?Sized, F> From<&'a VarZeroSlice<T, F>> for VarZeroVec<'a, T, F> {
177	0	fn from(other: &'a VarZeroSlice<T, F>) -> Self {
178	0	Self(VarZeroVecInner::Borrowed(other))
179	0	} Unexecuted instantiation: <zerovec::varzerovec::vec::VarZeroVec<zerovec::zerovec::slice::ZeroSlice<icu_properties::props::Script>> as core::convert::From<&zerovec::varzerovec::slice::VarZeroSlice<zerovec::zerovec::slice::ZeroSlice<icu_properties::props::Script>>>>::from Unexecuted instantiation: <zerovec::varzerovec::vec::VarZeroVec<str> as core::convert::From<&zerovec::varzerovec::slice::VarZeroSlice<str>>>::from Unexecuted instantiation: <zerovec::varzerovec::vec::VarZeroVec<_, _> as core::convert::From<&zerovec::varzerovec::slice::VarZeroSlice<_, _>>>::from
180		}
181
182		#[cfg(feature = "alloc")]
183		impl<'a, T: ?Sized + VarULE, F: VarZeroVecFormat> From<VarZeroVec<'a, T, F>>
184		for VarZeroVecOwned<T, F>
185		{
186		#[inline]
187	0	fn from(other: VarZeroVec<'a, T, F>) -> Self {
188	0	match other.0 {
189	0	VarZeroVecInner::Owned(o) => o,
190	0	VarZeroVecInner::Borrowed(b) => b.into(),
191		}
192	0	}
193		}
194
195		impl<T: VarULE + ?Sized, F: VarZeroVecFormat> Default for VarZeroVec<'_, T, F> {
196		#[inline]
197	0	fn default() -> Self {
198	0	Self::new()
199	0	}
200		}
201
202		impl<T: VarULE + ?Sized, F: VarZeroVecFormat> Deref for VarZeroVec<'_, T, F> {
203		type Target = VarZeroSlice<T, F>;
204	0	fn deref(&self) -> &VarZeroSlice<T, F> {
205	0	self.as_slice()
206	0	} Unexecuted instantiation: <zerovec::varzerovec::vec::VarZeroVec<zerovec::zerovec::slice::ZeroSlice<icu_properties::props::Script>> as core::ops::deref::Deref>::deref Unexecuted instantiation: <zerovec::varzerovec::vec::VarZeroVec<str> as core::ops::deref::Deref>::deref Unexecuted instantiation: <zerovec::varzerovec::vec::VarZeroVec<_, _> as core::ops::deref::Deref>::deref
207		}
208
209		impl<'a, T: VarULE + ?Sized, F: VarZeroVecFormat> VarZeroVec<'a, T, F> {
210		/// Creates a new, empty `VarZeroVec<T>`.
211		///
212		/// # Examples
213		///
214		/// ```
215		/// use zerovec::VarZeroVec;
216		///
217		/// let vzv: VarZeroVec<str> = VarZeroVec::new();
218		/// assert!(vzv.is_empty());
219		/// ```
220		#[inline]
221	0	pub const fn new() -> Self {
222	0	Self(VarZeroVecInner::Borrowed(VarZeroSlice::new_empty()))
223	0	}
224
225		/// Parse a VarZeroVec from a slice of the appropriate format
226		///
227		/// Slices of the right format can be obtained via [`VarZeroSlice::as_bytes()`].
228		///
229		/// # Example
230		///
231		/// ```rust
232		/// # use zerovec::VarZeroVec;
233		///
234		/// let strings = vec!["foo", "bar", "baz", "quux"];
235		/// let vec = VarZeroVec::<str>::from(&strings);
236		///
237		/// assert_eq!(&vec[0], "foo");
238		/// assert_eq!(&vec[1], "bar");
239		/// assert_eq!(&vec[2], "baz");
240		/// assert_eq!(&vec[3], "quux");
241		/// ```
242	0	pub fn parse_bytes(slice: &'a [u8]) -> Result<Self, UleError> {
243	0	let borrowed = VarZeroSlice::<T, F>::parse_bytes(slice)?;
244
245	0	Ok(Self(VarZeroVecInner::Borrowed(borrowed)))
246	0	}
247
248		/// Uses a `&[u8]` buffer as a `VarZeroVec<T>` without any verification.
249		///
250		/// # Safety
251		///
252		/// `bytes` need to be an output from [`VarZeroSlice::as_bytes()`].
253	0	pub const unsafe fn from_bytes_unchecked(bytes: &'a [u8]) -> Self {
254	0	Self(VarZeroVecInner::Borrowed(core::mem::transmute::<
255	0	&[u8],
256	0	&VarZeroSlice<T, F>,
257	0	>(bytes)))
258	0	}
259
260		/// Convert this into a mutable vector of the owned `T` type, cloning if necessary.
261		///
262		///
263		/// # Example
264		///
265		/// ```rust,ignore
266		/// # use zerovec::VarZeroVec;
267		/// let strings = vec!["foo", "bar", "baz", "quux"];
268		/// let mut vec = VarZeroVec::<str>::from(&strings);
269		///
270		/// assert_eq!(vec.len(), 4);
271		/// let mutvec = vec.make_mut();
272		/// mutvec.push("lorem ipsum".into());
273		/// mutvec[2] = "dolor sit".into();
274		/// assert_eq!(&vec[0], "foo");
275		/// assert_eq!(&vec[1], "bar");
276		/// assert_eq!(&vec[2], "dolor sit");
277		/// assert_eq!(&vec[3], "quux");
278		/// assert_eq!(&vec[4], "lorem ipsum");
279		/// ```
280		//
281		// This function is crate-public for now since we don't yet want to stabilize
282		// the internal implementation details
283		#[cfg(feature = "alloc")]
284	0	pub fn make_mut(&mut self) -> &mut VarZeroVecOwned<T, F> {
285	0	match self.0 {
286	0	VarZeroVecInner::Owned(ref mut vec) => vec,
287	0	VarZeroVecInner::Borrowed(slice) => {
288	0	let new_self = VarZeroVecOwned::from_slice(slice);
289	0	*self = new_self.into();
290		// recursion is limited since we are guaranteed to hit the Owned branch
291	0	self.make_mut()
292		}
293		}
294	0	}
295
296		/// Converts a borrowed ZeroVec to an owned ZeroVec. No-op if already owned.
297		///
298		/// # Example
299		///
300		/// ```
301		/// # use zerovec::VarZeroVec;
302		///
303		/// let strings = vec!["foo", "bar", "baz", "quux"];
304		/// let vec = VarZeroVec::<str>::from(&strings);
305		///
306		/// assert_eq!(vec.len(), 4);
307		/// // has 'static lifetime
308		/// let owned = vec.into_owned();
309		/// ```
310		#[cfg(feature = "alloc")]
311	0	pub fn into_owned(mut self) -> VarZeroVec<'static, T, F> {
312	0	self.make_mut();
313	0	match self.0 {
314	0	VarZeroVecInner::Owned(vec) => vec.into(),
315	0	_ => unreachable!(),
316		}
317	0	}
318
319		/// Obtain this `VarZeroVec` as a [`VarZeroSlice`]
320	0	pub fn as_slice(&self) -> &VarZeroSlice<T, F> {
321	0	match self.0 {
322		#[cfg(feature = "alloc")]
323	0	VarZeroVecInner::Owned(ref owned) => owned,
324	0	VarZeroVecInner::Borrowed(b) => b,
325		}
326	0	} Unexecuted instantiation: <zerovec::varzerovec::vec::VarZeroVec<zerovec::zerovec::slice::ZeroSlice<icu_properties::props::Script>>>::as_slice Unexecuted instantiation: <zerovec::varzerovec::vec::VarZeroVec<str>>::as_slice Unexecuted instantiation: <zerovec::varzerovec::vec::VarZeroVec<_, _>>::as_slice
327
328		/// Takes the byte vector representing the encoded data of this VarZeroVec. If borrowed,
329		/// this function allocates a byte vector and copies the borrowed bytes into it.
330		///
331		/// The bytes can be passed back to [`Self::parse_bytes()`].
332		///
333		/// To get a reference to the bytes without moving, see [`VarZeroSlice::as_bytes()`].
334		///
335		/// # Example
336		///
337		/// ```rust
338		/// # use zerovec::VarZeroVec;
339		///
340		/// let strings = vec!["foo", "bar", "baz"];
341		/// let bytes = VarZeroVec::<str>::from(&strings).into_bytes();
342		///
343		/// let mut borrowed: VarZeroVec<str> =
344		/// VarZeroVec::parse_bytes(&bytes).unwrap();
345		/// assert_eq!(borrowed, &*strings);
346		/// ```
347		#[cfg(feature = "alloc")]
348	0	pub fn into_bytes(self) -> alloc::vec::Vec<u8> {
349	0	match self.0 {
350		#[cfg(feature = "alloc")]
351	0	VarZeroVecInner::Owned(vec) => vec.into_bytes(),
352	0	VarZeroVecInner::Borrowed(vec) => vec.as_bytes().to_vec(),
353		}
354	0	}
355
356		/// Return whether the [`VarZeroVec`] is operating on owned or borrowed
357		/// data. [`VarZeroVec::into_owned()`] and [`VarZeroVec::make_mut()`] can
358		/// be used to force it into an owned type
359	0	pub fn is_owned(&self) -> bool {
360	0	match self.0 {
361		#[cfg(feature = "alloc")]
362	0	VarZeroVecInner::Owned(..) => true,
363	0	VarZeroVecInner::Borrowed(..) => false,
364		}
365	0	}
366
367		#[doc(hidden)]
368	0	pub fn as_components<'b>(&'b self) -> VarZeroVecComponents<'b, T, F> {
369	0	self.as_slice().as_components()
370	0	}
371		}
372
373		#[cfg(feature = "alloc")]
374		impl<A, T, F> From<&alloc::vec::Vec<A>> for VarZeroVec<'static, T, F>
375		where
376		T: VarULE + ?Sized,
377		A: EncodeAsVarULE<T>,
378		F: VarZeroVecFormat,
379		{
380		#[inline]
381	0	fn from(elements: &alloc::vec::Vec<A>) -> Self {
382	0	Self::from(elements.as_slice())
383	0	}
384		}
385
386		#[cfg(feature = "alloc")]
387		impl<A, T, F> From<&[A]> for VarZeroVec<'static, T, F>
388		where
389		T: VarULE + ?Sized,
390		A: EncodeAsVarULE<T>,
391		F: VarZeroVecFormat,
392		{
393		#[inline]
394	0	fn from(elements: &[A]) -> Self {
395	0	if elements.is_empty() {
396	0	VarZeroSlice::new_empty().into()
397		} else {
398		#[expect(clippy::unwrap_used)] // TODO(#1410) Better story for fallibility
399	0	VarZeroVecOwned::try_from_elements(elements).unwrap().into()
400		}
401	0	}
402		}
403
404		#[cfg(feature = "alloc")]
405		impl<A, T, F, const N: usize> From<&[A; N]> for VarZeroVec<'static, T, F>
406		where
407		T: VarULE + ?Sized,
408		A: EncodeAsVarULE<T>,
409		F: VarZeroVecFormat,
410		{
411		#[inline]
412	0	fn from(elements: &[A; N]) -> Self {
413	0	Self::from(elements.as_slice())
414	0	}
415		}
416
417		impl<'a, 'b, T, F> PartialEq<VarZeroVec<'b, T, F>> for VarZeroVec<'a, T, F>
418		where
419		T: VarULE,
420		T: ?Sized,
421		T: PartialEq,
422		F: VarZeroVecFormat,
423		{
424		#[inline]
425	0	fn eq(&self, other: &VarZeroVec<'b, T, F>) -> bool {
426		// VZV::from_elements used to produce a non-canonical representation of the
427		// empty VZV, so we cannot use byte equality for empty vecs.
428	0	if self.is_empty() \|\| other.is_empty() {
429	0	return self.is_empty() && other.is_empty();
430	0	}
431		// VarULE has an API guarantee that byte equality is semantic equality.
432		// For non-empty VZVs, there's only a single metadata representation,
433		// so this guarantee extends to the whole VZV representation.
434	0	self.as_bytes().eq(other.as_bytes())
435	0	}
436		}
437
438		impl<'a, T, F> Eq for VarZeroVec<'a, T, F>
439		where
440		T: VarULE,
441		T: ?Sized,
442		T: Eq,
443		F: VarZeroVecFormat,
444		{
445		}
446
447		impl<T, A, F> PartialEq<&'_ [A]> for VarZeroVec<'_, T, F>
448		where
449		T: VarULE + ?Sized,
450		T: PartialEq,
451		A: AsRef<T>,
452		F: VarZeroVecFormat,
453		{
454		#[inline]
455	0	fn eq(&self, other: &&[A]) -> bool {
456	0	self.iter().eq(other.iter().map(\|t\| t.as_ref()))
457	0	}
458		}
459
460		impl<T, A, F, const N: usize> PartialEq<[A; N]> for VarZeroVec<'_, T, F>
461		where
462		T: VarULE + ?Sized,
463		T: PartialEq,
464		A: AsRef<T>,
465		F: VarZeroVecFormat,
466		{
467		#[inline]
468	0	fn eq(&self, other: &[A; N]) -> bool {
469	0	self.iter().eq(other.iter().map(\|t\| t.as_ref()))
470	0	}
471		}
472
473		impl<'a, T: VarULE + ?Sized + PartialOrd, F: VarZeroVecFormat> PartialOrd for VarZeroVec<'a, T, F> {
474	0	fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
475	0	self.iter().partial_cmp(other.iter())
476	0	}
477		}
478
479		impl<'a, T: VarULE + ?Sized + Ord, F: VarZeroVecFormat> Ord for VarZeroVec<'a, T, F> {
480	0	fn cmp(&self, other: &Self) -> Ordering {
481	0	self.iter().cmp(other.iter())
482	0	}
483		}
484
485		#[test]
486		fn assert_single_empty_representation() {
487		assert_eq!(
488		VarZeroVec::<str>::new().as_bytes(),
489		VarZeroVec::<str>::from(&[] as &[&str]).as_bytes()
490		);
491
492		use crate::map::MutableZeroVecLike;
493		let mut vzv = VarZeroVec::<str>::from(&["hello", "world"][..]);
494		assert_eq!(vzv.len(), 2);
495		assert!(!vzv.as_bytes().is_empty());
496		vzv.zvl_remove(0);
497		assert_eq!(vzv.len(), 1);
498		assert!(!vzv.as_bytes().is_empty());
499		vzv.zvl_remove(0);
500		assert_eq!(vzv.len(), 0);
501		assert!(vzv.as_bytes().is_empty());
502		vzv.zvl_insert(0, "something");
503		assert_eq!(vzv.len(), 1);
504		assert!(!vzv.as_bytes().is_empty());
505		}
506
507		#[test]
508		fn weird_empty_representation_equality() {
509		assert_eq!(
510		VarZeroVec::<str>::parse_bytes(&[0, 0, 0, 0]).unwrap(),
511		VarZeroVec::<str>::parse_bytes(&[]).unwrap()
512		);
513		}