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//! Useful traits for manipulating sequences of data stored in `GenericArray`s
use super::*;
use core::mem::MaybeUninit;
use core::ops::{Add, Sub};
use core::ptr;
use typenum::operator_aliases::*;
/// Defines some sequence with an associated length and iteration capabilities.
///
/// This is useful for passing N-length generic arrays as generics.
///
/// # Safety
/// Care must be taken when implementing such that methods are safe.
///
/// Lengths must match, and element drop on panic must be handled.
pub unsafe trait GenericSequence<T>: Sized + IntoIterator {
/// `GenericArray` associated length
type Length: ArrayLength;
/// Owned sequence type used in conjuction with reference implementations of `GenericSequence`
type Sequence: GenericSequence<T, Length = Self::Length> + FromIterator<T>;
/// Initializes a new sequence instance using the given function.
///
/// If the generator function panics while initializing the sequence,
/// any already initialized elements will be dropped.
fn generate<F>(f: F) -> Self::Sequence
where
F: FnMut(usize) -> T;
/// Treats `self` as the right-hand operand in a zip operation
///
/// This is optimized for stack-allocated `GenericArray`s
#[cfg_attr(not(feature = "internals"), doc(hidden))]
#[inline(always)]
fn inverted_zip<B, U, F>(
self,
lhs: GenericArray<B, Self::Length>,
mut f: F,
) -> MappedSequence<GenericArray<B, Self::Length>, B, U>
where
GenericArray<B, Self::Length>:
GenericSequence<B, Length = Self::Length> + MappedGenericSequence<B, U>,
Self: MappedGenericSequence<T, U>,
F: FnMut(B, Self::Item) -> U,
{
unsafe {
let mut left = ArrayConsumer::new(lhs);
let (left_array_iter, left_position) = left.iter_position();
FromIterator::from_iter(left_array_iter.zip(self).map(|(l, right_value)| {
let left_value = ptr::read(l);
*left_position += 1;
f(left_value, right_value)
}))
}
}
/// Treats `self` as the right-hand operand in a zip operation
#[cfg_attr(not(feature = "internals"), doc(hidden))]
#[inline(always)]
fn inverted_zip2<B, Lhs, U, F>(self, lhs: Lhs, mut f: F) -> MappedSequence<Lhs, B, U>
where
Lhs: GenericSequence<B, Length = Self::Length> + MappedGenericSequence<B, U>,
Self: MappedGenericSequence<T, U>,
F: FnMut(Lhs::Item, Self::Item) -> U,
{
FromIterator::from_iter(lhs.into_iter().zip(self).map(|(l, r)| f(l, r)))
}
}
/// Accessor for `GenericSequence` item type, which is really `IntoIterator::Item`
///
/// For deeply nested generic mapped sequence types, like shown in `tests/generics.rs`,
/// this can be useful for keeping things organized.
pub type SequenceItem<T> = <T as IntoIterator>::Item;
unsafe impl<'a, T: 'a, S: GenericSequence<T>> GenericSequence<T> for &'a S
where
&'a S: IntoIterator,
{
type Length = S::Length;
type Sequence = S::Sequence;
#[inline(always)]
fn generate<F>(f: F) -> Self::Sequence
where
F: FnMut(usize) -> T,
{
S::generate(f)
}
}
unsafe impl<'a, T: 'a, S: GenericSequence<T>> GenericSequence<T> for &'a mut S
where
&'a mut S: IntoIterator,
{
type Length = S::Length;
type Sequence = S::Sequence;
#[inline(always)]
fn generate<F>(f: F) -> Self::Sequence
where
F: FnMut(usize) -> T,
{
S::generate(f)
}
}
/// Defines any `GenericSequence` which can be lengthened or extended by appending
/// or prepending an element to it.
///
/// Any lengthened sequence can be shortened back to the original using `pop_front` or `pop_back`
///
/// # Safety
/// While the [`append`](Lengthen::append) and [`prepend`](Lengthen::prepend)
/// methods are marked safe, care must be taken when implementing them.
pub unsafe trait Lengthen<T>: Sized + GenericSequence<T> {
/// `GenericSequence` that has one more element than `Self`
type Longer: Shorten<T, Shorter = Self>;
/// Returns a new array with the given element appended to the end of it.
///
/// Example:
///
/// ```rust
/// # use generic_array::{arr, sequence::Lengthen};
///
/// let a = arr![1, 2, 3];
///
/// let b = a.append(4);
///
/// assert_eq!(b, arr![1, 2, 3, 4]);
/// ```
fn append(self, last: T) -> Self::Longer;
/// Returns a new array with the given element prepended to the front of it.
///
/// Example:
///
/// ```rust
/// # use generic_array::{arr, sequence::Lengthen};
///
/// let a = arr![1, 2, 3];
///
/// let b = a.prepend(4);
///
/// assert_eq!(b, arr![4, 1, 2, 3]);
/// ```
fn prepend(self, first: T) -> Self::Longer;
}
/// Defines a `GenericSequence` which can be shortened by removing the first or last element from it.
///
/// Additionally, any shortened sequence can be lengthened by
/// appending or prepending an element to it.
///
/// # Safety
/// While the [`pop_back`](Shorten::pop_back) and [`pop_front`](Shorten::pop_front)
/// methods are marked safe, care must be taken when implementing them.
pub unsafe trait Shorten<T>: Sized + GenericSequence<T> {
/// `GenericSequence` that has one less element than `Self`
type Shorter: Lengthen<T, Longer = Self>;
/// Returns a new array without the last element, and the last element.
///
/// Example:
///
/// ```rust
/// # use generic_array::{arr, sequence::Shorten};
///
/// let a = arr![1, 2, 3, 4];
///
/// let (init, last) = a.pop_back();
///
/// assert_eq!(init, arr![1, 2, 3]);
/// assert_eq!(last, 4);
/// ```
fn pop_back(self) -> (Self::Shorter, T);
/// Returns a new array without the first element, and the first element.
/// Example:
///
/// ```rust
/// # use generic_array::{arr, sequence::Shorten};
///
/// let a = arr![1, 2, 3, 4];
///
/// let (head, tail) = a.pop_front();
///
/// assert_eq!(head, 1);
/// assert_eq!(tail, arr![2, 3, 4]);
/// ```
fn pop_front(self) -> (T, Self::Shorter);
}
unsafe impl<T, N: ArrayLength> Lengthen<T> for GenericArray<T, N>
where
N: Add<B1>,
Add1<N>: ArrayLength,
Add1<N>: Sub<B1, Output = N>,
Sub1<Add1<N>>: ArrayLength,
{
type Longer = GenericArray<T, Add1<N>>;
#[inline]
fn append(self, last: T) -> Self::Longer {
let mut longer: MaybeUninit<Self::Longer> = MaybeUninit::uninit();
// Note this is *mut Self, so add(1) increments by the whole array
let out_ptr = longer.as_mut_ptr() as *mut Self;
unsafe {
// write self first
ptr::write(out_ptr, self);
// increment past self, then write the last
ptr::write(out_ptr.add(1) as *mut T, last);
longer.assume_init()
}
}
#[inline]
fn prepend(self, first: T) -> Self::Longer {
let mut longer: MaybeUninit<Self::Longer> = MaybeUninit::uninit();
// Note this is *mut T, so add(1) increments by a single T
let out_ptr = longer.as_mut_ptr() as *mut T;
unsafe {
// write the first at the start
ptr::write(out_ptr, first);
// increment past the first, then write self
ptr::write(out_ptr.add(1) as *mut Self, self);
longer.assume_init()
}
}
}
unsafe impl<T, N: ArrayLength> Shorten<T> for GenericArray<T, N>
where
N: Sub<B1>,
Sub1<N>: ArrayLength,
Sub1<N>: Add<B1, Output = N>,
Add1<Sub1<N>>: ArrayLength,
{
type Shorter = GenericArray<T, Sub1<N>>;
#[inline]
fn pop_back(self) -> (Self::Shorter, T) {
let whole = ManuallyDrop::new(self);
unsafe {
let init = ptr::read(whole.as_ptr() as _);
let last = ptr::read(whole.as_ptr().add(Sub1::<N>::USIZE) as _);
(init, last)
}
}
#[inline]
fn pop_front(self) -> (T, Self::Shorter) {
// ensure this doesn't get dropped
let whole = ManuallyDrop::new(self);
unsafe {
let head = ptr::read(whole.as_ptr() as _);
let tail = ptr::read(whole.as_ptr().offset(1) as _);
(head, tail)
}
}
}
/// Defines a `GenericSequence` that can be split into two parts at a given pivot index.
///
/// # Safety
/// While the [`split`](Split::split) method is marked safe,
/// care must be taken when implementing it.
pub unsafe trait Split<T, K: ArrayLength>: GenericSequence<T> {
/// First part of the resulting split array
type First: GenericSequence<T>;
/// Second part of the resulting split array
type Second: GenericSequence<T>;
/// Splits an array at the given index, returning the separate parts of the array.
fn split(self) -> (Self::First, Self::Second);
}
unsafe impl<T, N, K> Split<T, K> for GenericArray<T, N>
where
N: ArrayLength,
K: ArrayLength,
N: Sub<K>,
Diff<N, K>: ArrayLength,
{
type First = GenericArray<T, K>;
type Second = GenericArray<T, Diff<N, K>>;
#[inline]
fn split(self) -> (Self::First, Self::Second) {
unsafe {
// ensure this doesn't get dropped
let whole = ManuallyDrop::new(self);
let head = ptr::read(whole.as_ptr() as *const _);
let tail = ptr::read(whole.as_ptr().add(K::USIZE) as *const _);
(head, tail)
}
}
}
unsafe impl<'a, T, N, K> Split<T, K> for &'a GenericArray<T, N>
where
N: ArrayLength,
K: ArrayLength,
N: Sub<K>,
Diff<N, K>: ArrayLength,
{
type First = &'a GenericArray<T, K>;
type Second = &'a GenericArray<T, Diff<N, K>>;
#[inline]
fn split(self) -> (Self::First, Self::Second) {
unsafe {
let ptr_to_first: *const T = self.as_ptr();
let head = &*(ptr_to_first as *const _);
let tail = &*(ptr_to_first.add(K::USIZE) as *const _);
(head, tail)
}
}
}
unsafe impl<'a, T, N, K> Split<T, K> for &'a mut GenericArray<T, N>
where
N: ArrayLength,
K: ArrayLength,
N: Sub<K>,
Diff<N, K>: ArrayLength,
{
type First = &'a mut GenericArray<T, K>;
type Second = &'a mut GenericArray<T, Diff<N, K>>;
#[inline]
fn split(self) -> (Self::First, Self::Second) {
unsafe {
let ptr_to_first: *mut T = self.as_mut_ptr();
let head = &mut *(ptr_to_first as *mut _);
let tail = &mut *(ptr_to_first.add(K::USIZE) as *mut _);
(head, tail)
}
}
}
/// Defines `GenericSequence`s which can be joined together, forming a larger array.
///
/// # Safety
/// While the [`concat`](Concat::concat) method is marked safe,
/// care must be taken when implementing it.
pub unsafe trait Concat<T, M: ArrayLength>: GenericSequence<T> {
/// Sequence to be concatenated with `self`
type Rest: GenericSequence<T, Length = M>;
/// Resulting sequence formed by the concatenation.
type Output: GenericSequence<T>;
/// Concatenate, or join, two sequences.
fn concat(self, rest: Self::Rest) -> Self::Output;
}
unsafe impl<T, N, M> Concat<T, M> for GenericArray<T, N>
where
N: ArrayLength + Add<M>,
M: ArrayLength,
Sum<N, M>: ArrayLength,
{
type Rest = GenericArray<T, M>;
type Output = GenericArray<T, Sum<N, M>>;
#[inline]
fn concat(self, rest: Self::Rest) -> Self::Output {
let mut output: MaybeUninit<Self::Output> = MaybeUninit::uninit();
let out_ptr = output.as_mut_ptr() as *mut Self;
unsafe {
// write all of self to the pointer
ptr::write(out_ptr, self);
// increment past self, then write the rest
ptr::write(out_ptr.add(1) as *mut _, rest);
output.assume_init()
}
}
}
/// Defines a `GenericSequence` which can be shortened by removing an element at a given index.
///
/// # Safety
/// While the [`remove`](Remove::remove) and [`swap_remove`](Remove::swap_remove) methods are marked safe,
/// care must be taken when implementing it. The [`remove_unchecked`](Remove::remove_unchecked)
/// and [`swap_remove_unchecked`](Remove::swap_remove_unchecked) methods are unsafe
/// and must be used with caution.
pub unsafe trait Remove<T, N: ArrayLength>: GenericSequence<T> {
/// Resulting sequence formed by removing an element at the given index.
type Output: GenericSequence<T>;
/// Removes an element at the given index, shifting elements
/// after the given index to the left to fill the gap, resulting
/// in a time complexity of O(n) where `n=N-idx-1`
///
/// # Example
///
/// ```rust
/// # use generic_array::{arr, sequence::Remove};
/// let a = arr![1, 2, 3, 4];
///
/// let (removed, b) = a.remove(2);
/// assert_eq!(removed, 3);
/// assert_eq!(b, arr![1, 2, 4]);
/// ```
///
/// # Panics
///
/// Panics if the index is out of bounds.
#[inline]
fn remove(self, idx: usize) -> (T, Self::Output) {
assert!(
idx < N::USIZE,
"Index out of bounds: the len is {} but the index is {}",
N::USIZE,
idx
);
unsafe { self.remove_unchecked(idx) }
}
/// Removes an element at the given index, swapping it with the last element.
///
/// # Example
///
/// ```rust
/// # use generic_array::{arr, sequence::Remove};
/// let a = arr![1, 2, 3, 4];
///
/// let (removed, b) = a.swap_remove(1);
/// assert_eq!(removed, 2);
/// assert_eq!(b, arr![1, 4, 3]); // note 4 is now at index 1
/// ```
///
/// # Panics
///
/// Panics if the index is out of bounds.
fn swap_remove(self, idx: usize) -> (T, Self::Output) {
assert!(
idx < N::USIZE,
"Index out of bounds: the len is {} but the index is {}",
N::USIZE,
idx
);
unsafe { self.swap_remove_unchecked(idx) }
}
/// Removes an element at the given index without bounds checking,
/// shifting elements after the given index to the left to fill the gap,
/// resulting in a time complexity of O(n) where `n=N-idx-1`
///
/// See [`remove`](Remove::remove) for an example.
///
/// # Safety
/// The caller must ensure that the index is within bounds, otherwise
/// it is undefined behavior.
unsafe fn remove_unchecked(self, idx: usize) -> (T, Self::Output);
/// Removes an element at the given index without bounds checking, swapping it with the last element.
///
/// See [`swap_remove`](Remove::swap_remove) for an example.
///
/// # Safety
/// The caller must ensure that the index is within bounds, otherwise
/// it is undefined behavior.
unsafe fn swap_remove_unchecked(self, idx: usize) -> (T, Self::Output);
}
unsafe impl<T, N> Remove<T, N> for GenericArray<T, N>
where
N: ArrayLength + Sub<B1>,
Sub1<N>: ArrayLength,
{
type Output = GenericArray<T, Sub1<N>>;
#[inline]
unsafe fn remove_unchecked(self, idx: usize) -> (T, Self::Output) {
if idx >= N::USIZE || N::USIZE == 0 {
core::hint::unreachable_unchecked();
}
let mut array = ManuallyDrop::new(self);
let dst = array.as_mut_ptr().add(idx);
let removed = ptr::read(dst);
// shift all elements over by one to fill gap
ptr::copy(dst.add(1), dst, N::USIZE - idx - 1);
// return removed element and truncated array
(removed, mem::transmute_copy(&array))
}
#[inline]
unsafe fn swap_remove_unchecked(self, idx: usize) -> (T, Self::Output) {
if idx >= N::USIZE || N::USIZE == 0 {
core::hint::unreachable_unchecked();
}
let mut array = ManuallyDrop::new(self);
array.swap(idx, N::USIZE - 1);
// remove the last element
let removed = ptr::read(array.as_ptr().add(N::USIZE - 1));
// return removed element and truncated array
(removed, mem::transmute_copy(&array))
}
}