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immutable.rs
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immutable.rs
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use either::Either;
use std::{iter::FromIterator, sync::Arc, usize};
use crate::types::NativeType;
use super::bytes::Bytes;
/// [`Buffer`] is a contiguous memory region that can be shared across thread boundaries.
///
/// The easiest way to think about `Buffer<T>` is being equivalent to
/// a `Arc<Vec<T>>`, with the following differences:
/// * `T` must be [`NativeType`]
/// * slicing the buffer is `O(1)`
/// * it supports external allocated memory (via FFI)
///
/// The easiest way to create one is to use its implementation of `From` a `Vec`.
///
/// # Examples
/// ```
/// use arrow2::buffer::Buffer;
///
/// let buffer: Buffer<u32> = vec![1, 2, 3].into();
/// assert_eq!(buffer.as_ref(), [1, 2, 3].as_ref());
///
/// // it supports copy-on-write semantics (i.e. back to a `Vec`)
/// let vec: Vec<u32> = buffer.into_mut().right().unwrap();
/// assert_eq!(vec, vec![1, 2, 3]);
///
/// // cloning and slicing is `O(1)` (data is shared)
/// let buffer: Buffer<u32> = vec![1, 2, 3].into();
/// let slice = buffer.clone().slice(1, 1);
/// assert_eq!(slice.as_ref(), [2].as_ref());
/// // no longer possible to get a vec since `slice` and `buffer` share data
/// let same: Buffer<u32> = buffer.into_mut().left().unwrap();
/// ```
#[derive(Clone, PartialEq)]
pub struct Buffer<T: NativeType> {
/// the internal byte buffer.
data: Arc<Bytes<T>>,
/// The offset into the buffer.
offset: usize,
// the length of the buffer. Given a region `data` of N bytes, [offset..offset+length] is visible
// to this buffer.
length: usize,
}
impl<T: NativeType> std::fmt::Debug for Buffer<T> {
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
std::fmt::Debug::fmt(&**self, f)
}
}
impl<T: NativeType> Default for Buffer<T> {
#[inline]
fn default() -> Self {
Vec::new().into()
}
}
impl<T: NativeType> Buffer<T> {
/// Creates an empty [`Buffer`].
#[inline]
pub fn new() -> Self {
Self::default()
}
/// Auxiliary method to create a new Buffer
pub(crate) fn from_bytes(bytes: Bytes<T>) -> Self {
let length = bytes.len();
Buffer {
data: Arc::new(bytes),
offset: 0,
length,
}
}
/// Returns the number of bytes in the buffer
#[inline]
pub fn len(&self) -> usize {
self.length
}
/// Returns whether the buffer is empty.
#[inline]
pub fn is_empty(&self) -> bool {
self.len() == 0
}
/// Returns the byte slice stored in this buffer
#[inline]
pub fn as_slice(&self) -> &[T] {
// Safety:
// invariant of this struct `offset + length <= data.len()`
debug_assert!(self.offset + self.length <= self.data.len());
unsafe {
self.data
.get_unchecked(self.offset..self.offset + self.length)
}
}
/// Returns a new [Buffer] that is a slice of this buffer starting at `offset`.
/// Doing so allows the same memory region to be shared between buffers.
/// # Panics
/// Panics iff `offset` is larger than `len`.
#[inline]
pub fn slice(self, offset: usize, length: usize) -> Self {
assert!(
offset + length <= self.len(),
"the offset of the new Buffer cannot exceed the existing length"
);
// Safety: we just checked bounds
unsafe { self.slice_unchecked(offset, length) }
}
/// Returns a new [Buffer] that is a slice of this buffer starting at `offset`.
/// Doing so allows the same memory region to be shared between buffers.
/// # Safety
/// The caller must ensure `offset + length <= self.len()`
#[inline]
pub unsafe fn slice_unchecked(mut self, offset: usize, length: usize) -> Self {
self.offset += offset;
self.length = length;
self
}
/// Returns a pointer to the start of this buffer.
#[inline]
pub(crate) fn as_ptr(&self) -> std::ptr::NonNull<T> {
self.data.ptr()
}
/// Returns the offset of this buffer.
#[inline]
pub fn offset(&self) -> usize {
self.offset
}
/// Converts this [`Buffer`] to [`Vec`], returning itself if the conversion
/// is not possible
///
/// This operation returns a [`Vec`] iff this [`Buffer`]:
/// * is not an offsetted slice of another [`Buffer`]
/// * has not been cloned (i.e. [`Arc`]`::get_mut` yields [`Some`])
/// * has not been imported from the c data interface (FFI)
pub fn into_mut(mut self) -> Either<Self, Vec<T>> {
if self.offset != 0 {
Either::Left(self)
} else {
match Arc::get_mut(&mut self.data).and_then(|b| b.get_vec()) {
Some(v) => {
let data = std::mem::take(v);
Either::Right(data)
}
None => Either::Left(self),
}
}
}
}
impl<T: NativeType> From<Vec<T>> for Buffer<T> {
#[inline]
fn from(p: Vec<T>) -> Self {
let bytes: Bytes<T> = p.into();
Self {
offset: 0,
length: bytes.len(),
data: Arc::new(bytes),
}
}
}
impl<T: NativeType> std::ops::Deref for Buffer<T> {
type Target = [T];
#[inline]
fn deref(&self) -> &[T] {
self.as_slice()
}
}
impl<T: NativeType> FromIterator<T> for Buffer<T> {
#[inline]
fn from_iter<I: IntoIterator<Item = T>>(iter: I) -> Self {
Vec::from_iter(iter).into()
}
}