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Diffstat (limited to 'library/core/src/array/mod.rs')
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diff --git a/library/core/src/array/mod.rs b/library/core/src/array/mod.rs new file mode 100644 index 000000000..c9823a136 --- /dev/null +++ b/library/core/src/array/mod.rs @@ -0,0 +1,872 @@ +//! Helper functions and types for fixed-length arrays. +//! +//! *[See also the array primitive type](array).* + +#![stable(feature = "core_array", since = "1.36.0")] + +use crate::borrow::{Borrow, BorrowMut}; +use crate::cmp::Ordering; +use crate::convert::{Infallible, TryFrom}; +use crate::fmt; +use crate::hash::{self, Hash}; +use crate::iter::TrustedLen; +use crate::mem::{self, MaybeUninit}; +use crate::ops::{ + ChangeOutputType, ControlFlow, FromResidual, Index, IndexMut, NeverShortCircuit, Residual, Try, +}; +use crate::slice::{Iter, IterMut}; + +mod equality; +mod iter; + +#[stable(feature = "array_value_iter", since = "1.51.0")] +pub use iter::IntoIter; + +/// Creates an array `[T; N]` where each array element `T` is returned by the `cb` call. +/// +/// # Arguments +/// +/// * `cb`: Callback where the passed argument is the current array index. +/// +/// # Example +/// +/// ```rust +/// let array = core::array::from_fn(|i| i); +/// assert_eq!(array, [0, 1, 2, 3, 4]); +/// ``` +#[inline] +#[stable(feature = "array_from_fn", since = "1.63.0")] +pub fn from_fn<T, const N: usize, F>(mut cb: F) -> [T; N] +where + F: FnMut(usize) -> T, +{ + let mut idx = 0; + [(); N].map(|_| { + let res = cb(idx); + idx += 1; + res + }) +} + +/// Creates an array `[T; N]` where each fallible array element `T` is returned by the `cb` call. +/// Unlike [`from_fn`], where the element creation can't fail, this version will return an error +/// if any element creation was unsuccessful. +/// +/// The return type of this function depends on the return type of the closure. +/// If you return `Result<T, E>` from the closure, you'll get a `Result<[T; N]; E>`. +/// If you return `Option<T>` from the closure, you'll get an `Option<[T; N]>`. +/// +/// # Arguments +/// +/// * `cb`: Callback where the passed argument is the current array index. +/// +/// # Example +/// +/// ```rust +/// #![feature(array_try_from_fn)] +/// +/// let array: Result<[u8; 5], _> = std::array::try_from_fn(|i| i.try_into()); +/// assert_eq!(array, Ok([0, 1, 2, 3, 4])); +/// +/// let array: Result<[i8; 200], _> = std::array::try_from_fn(|i| i.try_into()); +/// assert!(array.is_err()); +/// +/// let array: Option<[_; 4]> = std::array::try_from_fn(|i| i.checked_add(100)); +/// assert_eq!(array, Some([100, 101, 102, 103])); +/// +/// let array: Option<[_; 4]> = std::array::try_from_fn(|i| i.checked_sub(100)); +/// assert_eq!(array, None); +/// ``` +#[inline] +#[unstable(feature = "array_try_from_fn", issue = "89379")] +pub fn try_from_fn<R, const N: usize, F>(cb: F) -> ChangeOutputType<R, [R::Output; N]> +where + F: FnMut(usize) -> R, + R: Try, + R::Residual: Residual<[R::Output; N]>, +{ + // SAFETY: we know for certain that this iterator will yield exactly `N` + // items. + unsafe { try_collect_into_array_unchecked(&mut (0..N).map(cb)) } +} + +/// Converts a reference to `T` into a reference to an array of length 1 (without copying). +#[stable(feature = "array_from_ref", since = "1.53.0")] +#[rustc_const_stable(feature = "const_array_from_ref_shared", since = "1.63.0")] +pub const fn from_ref<T>(s: &T) -> &[T; 1] { + // SAFETY: Converting `&T` to `&[T; 1]` is sound. + unsafe { &*(s as *const T).cast::<[T; 1]>() } +} + +/// Converts a mutable reference to `T` into a mutable reference to an array of length 1 (without copying). +#[stable(feature = "array_from_ref", since = "1.53.0")] +#[rustc_const_unstable(feature = "const_array_from_ref", issue = "90206")] +pub const fn from_mut<T>(s: &mut T) -> &mut [T; 1] { + // SAFETY: Converting `&mut T` to `&mut [T; 1]` is sound. + unsafe { &mut *(s as *mut T).cast::<[T; 1]>() } +} + +/// The error type returned when a conversion from a slice to an array fails. +#[stable(feature = "try_from", since = "1.34.0")] +#[derive(Debug, Copy, Clone)] +pub struct TryFromSliceError(()); + +#[stable(feature = "core_array", since = "1.36.0")] +impl fmt::Display for TryFromSliceError { + #[inline] + fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { + fmt::Display::fmt(self.__description(), f) + } +} + +impl TryFromSliceError { + #[unstable( + feature = "array_error_internals", + reason = "available through Error trait and this method should not \ + be exposed publicly", + issue = "none" + )] + #[inline] + #[doc(hidden)] + pub fn __description(&self) -> &str { + "could not convert slice to array" + } +} + +#[stable(feature = "try_from_slice_error", since = "1.36.0")] +#[rustc_const_unstable(feature = "const_convert", issue = "88674")] +impl const From<Infallible> for TryFromSliceError { + fn from(x: Infallible) -> TryFromSliceError { + match x {} + } +} + +#[stable(feature = "rust1", since = "1.0.0")] +impl<T, const N: usize> AsRef<[T]> for [T; N] { + #[inline] + fn as_ref(&self) -> &[T] { + &self[..] + } +} + +#[stable(feature = "rust1", since = "1.0.0")] +impl<T, const N: usize> AsMut<[T]> for [T; N] { + #[inline] + fn as_mut(&mut self) -> &mut [T] { + &mut self[..] + } +} + +#[stable(feature = "array_borrow", since = "1.4.0")] +#[rustc_const_unstable(feature = "const_borrow", issue = "91522")] +impl<T, const N: usize> const Borrow<[T]> for [T; N] { + fn borrow(&self) -> &[T] { + self + } +} + +#[stable(feature = "array_borrow", since = "1.4.0")] +#[rustc_const_unstable(feature = "const_borrow", issue = "91522")] +impl<T, const N: usize> const BorrowMut<[T]> for [T; N] { + fn borrow_mut(&mut self) -> &mut [T] { + self + } +} + +#[stable(feature = "try_from", since = "1.34.0")] +impl<T, const N: usize> TryFrom<&[T]> for [T; N] +where + T: Copy, +{ + type Error = TryFromSliceError; + + fn try_from(slice: &[T]) -> Result<[T; N], TryFromSliceError> { + <&Self>::try_from(slice).map(|r| *r) + } +} + +#[stable(feature = "try_from_mut_slice_to_array", since = "1.59.0")] +impl<T, const N: usize> TryFrom<&mut [T]> for [T; N] +where + T: Copy, +{ + type Error = TryFromSliceError; + + fn try_from(slice: &mut [T]) -> Result<[T; N], TryFromSliceError> { + <Self>::try_from(&*slice) + } +} + +#[stable(feature = "try_from", since = "1.34.0")] +impl<'a, T, const N: usize> TryFrom<&'a [T]> for &'a [T; N] { + type Error = TryFromSliceError; + + fn try_from(slice: &[T]) -> Result<&[T; N], TryFromSliceError> { + if slice.len() == N { + let ptr = slice.as_ptr() as *const [T; N]; + // SAFETY: ok because we just checked that the length fits + unsafe { Ok(&*ptr) } + } else { + Err(TryFromSliceError(())) + } + } +} + +#[stable(feature = "try_from", since = "1.34.0")] +impl<'a, T, const N: usize> TryFrom<&'a mut [T]> for &'a mut [T; N] { + type Error = TryFromSliceError; + + fn try_from(slice: &mut [T]) -> Result<&mut [T; N], TryFromSliceError> { + if slice.len() == N { + let ptr = slice.as_mut_ptr() as *mut [T; N]; + // SAFETY: ok because we just checked that the length fits + unsafe { Ok(&mut *ptr) } + } else { + Err(TryFromSliceError(())) + } + } +} + +/// The hash of an array is the same as that of the corresponding slice, +/// as required by the `Borrow` implementation. +/// +/// ``` +/// #![feature(build_hasher_simple_hash_one)] +/// use std::hash::BuildHasher; +/// +/// let b = std::collections::hash_map::RandomState::new(); +/// let a: [u8; 3] = [0xa8, 0x3c, 0x09]; +/// let s: &[u8] = &[0xa8, 0x3c, 0x09]; +/// assert_eq!(b.hash_one(a), b.hash_one(s)); +/// ``` +#[stable(feature = "rust1", since = "1.0.0")] +impl<T: Hash, const N: usize> Hash for [T; N] { + fn hash<H: hash::Hasher>(&self, state: &mut H) { + Hash::hash(&self[..], state) + } +} + +#[stable(feature = "rust1", since = "1.0.0")] +impl<T: fmt::Debug, const N: usize> fmt::Debug for [T; N] { + fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { + fmt::Debug::fmt(&&self[..], f) + } +} + +#[stable(feature = "rust1", since = "1.0.0")] +impl<'a, T, const N: usize> IntoIterator for &'a [T; N] { + type Item = &'a T; + type IntoIter = Iter<'a, T>; + + fn into_iter(self) -> Iter<'a, T> { + self.iter() + } +} + +#[stable(feature = "rust1", since = "1.0.0")] +impl<'a, T, const N: usize> IntoIterator for &'a mut [T; N] { + type Item = &'a mut T; + type IntoIter = IterMut<'a, T>; + + fn into_iter(self) -> IterMut<'a, T> { + self.iter_mut() + } +} + +#[stable(feature = "index_trait_on_arrays", since = "1.50.0")] +#[rustc_const_unstable(feature = "const_slice_index", issue = "none")] +impl<T, I, const N: usize> const Index<I> for [T; N] +where + [T]: ~const Index<I>, +{ + type Output = <[T] as Index<I>>::Output; + + #[inline] + fn index(&self, index: I) -> &Self::Output { + Index::index(self as &[T], index) + } +} + +#[stable(feature = "index_trait_on_arrays", since = "1.50.0")] +#[rustc_const_unstable(feature = "const_slice_index", issue = "none")] +impl<T, I, const N: usize> const IndexMut<I> for [T; N] +where + [T]: ~const IndexMut<I>, +{ + #[inline] + fn index_mut(&mut self, index: I) -> &mut Self::Output { + IndexMut::index_mut(self as &mut [T], index) + } +} + +#[stable(feature = "rust1", since = "1.0.0")] +impl<T: PartialOrd, const N: usize> PartialOrd for [T; N] { + #[inline] + fn partial_cmp(&self, other: &[T; N]) -> Option<Ordering> { + PartialOrd::partial_cmp(&&self[..], &&other[..]) + } + #[inline] + fn lt(&self, other: &[T; N]) -> bool { + PartialOrd::lt(&&self[..], &&other[..]) + } + #[inline] + fn le(&self, other: &[T; N]) -> bool { + PartialOrd::le(&&self[..], &&other[..]) + } + #[inline] + fn ge(&self, other: &[T; N]) -> bool { + PartialOrd::ge(&&self[..], &&other[..]) + } + #[inline] + fn gt(&self, other: &[T; N]) -> bool { + PartialOrd::gt(&&self[..], &&other[..]) + } +} + +/// Implements comparison of arrays [lexicographically](Ord#lexicographical-comparison). +#[stable(feature = "rust1", since = "1.0.0")] +impl<T: Ord, const N: usize> Ord for [T; N] { + #[inline] + fn cmp(&self, other: &[T; N]) -> Ordering { + Ord::cmp(&&self[..], &&other[..]) + } +} + +#[stable(feature = "copy_clone_array_lib", since = "1.58.0")] +impl<T: Copy, const N: usize> Copy for [T; N] {} + +#[stable(feature = "copy_clone_array_lib", since = "1.58.0")] +impl<T: Clone, const N: usize> Clone for [T; N] { + #[inline] + fn clone(&self) -> Self { + SpecArrayClone::clone(self) + } + + #[inline] + fn clone_from(&mut self, other: &Self) { + self.clone_from_slice(other); + } +} + +trait SpecArrayClone: Clone { + fn clone<const N: usize>(array: &[Self; N]) -> [Self; N]; +} + +impl<T: Clone> SpecArrayClone for T { + #[inline] + default fn clone<const N: usize>(array: &[T; N]) -> [T; N] { + // SAFETY: we know for certain that this iterator will yield exactly `N` + // items. + unsafe { collect_into_array_unchecked(&mut array.iter().cloned()) } + } +} + +impl<T: Copy> SpecArrayClone for T { + #[inline] + fn clone<const N: usize>(array: &[T; N]) -> [T; N] { + *array + } +} + +// The Default impls cannot be done with const generics because `[T; 0]` doesn't +// require Default to be implemented, and having different impl blocks for +// different numbers isn't supported yet. + +macro_rules! array_impl_default { + {$n:expr, $t:ident $($ts:ident)*} => { + #[stable(since = "1.4.0", feature = "array_default")] + impl<T> Default for [T; $n] where T: Default { + fn default() -> [T; $n] { + [$t::default(), $($ts::default()),*] + } + } + array_impl_default!{($n - 1), $($ts)*} + }; + {$n:expr,} => { + #[stable(since = "1.4.0", feature = "array_default")] + #[rustc_const_unstable(feature = "const_default_impls", issue = "87864")] + impl<T> const Default for [T; $n] { + fn default() -> [T; $n] { [] } + } + }; +} + +array_impl_default! {32, T T T T T T T T T T T T T T T T T T T T T T T T T T T T T T T T} + +impl<T, const N: usize> [T; N] { + /// Returns an array of the same size as `self`, with function `f` applied to each element + /// in order. + /// + /// If you don't necessarily need a new fixed-size array, consider using + /// [`Iterator::map`] instead. + /// + /// + /// # Note on performance and stack usage + /// + /// Unfortunately, usages of this method are currently not always optimized + /// as well as they could be. This mainly concerns large arrays, as mapping + /// over small arrays seem to be optimized just fine. Also note that in + /// debug mode (i.e. without any optimizations), this method can use a lot + /// of stack space (a few times the size of the array or more). + /// + /// Therefore, in performance-critical code, try to avoid using this method + /// on large arrays or check the emitted code. Also try to avoid chained + /// maps (e.g. `arr.map(...).map(...)`). + /// + /// In many cases, you can instead use [`Iterator::map`] by calling `.iter()` + /// or `.into_iter()` on your array. `[T; N]::map` is only necessary if you + /// really need a new array of the same size as the result. Rust's lazy + /// iterators tend to get optimized very well. + /// + /// + /// # Examples + /// + /// ``` + /// let x = [1, 2, 3]; + /// let y = x.map(|v| v + 1); + /// assert_eq!(y, [2, 3, 4]); + /// + /// let x = [1, 2, 3]; + /// let mut temp = 0; + /// let y = x.map(|v| { temp += 1; v * temp }); + /// assert_eq!(y, [1, 4, 9]); + /// + /// let x = ["Ferris", "Bueller's", "Day", "Off"]; + /// let y = x.map(|v| v.len()); + /// assert_eq!(y, [6, 9, 3, 3]); + /// ``` + #[stable(feature = "array_map", since = "1.55.0")] + pub fn map<F, U>(self, f: F) -> [U; N] + where + F: FnMut(T) -> U, + { + // SAFETY: we know for certain that this iterator will yield exactly `N` + // items. + unsafe { collect_into_array_unchecked(&mut IntoIterator::into_iter(self).map(f)) } + } + + /// A fallible function `f` applied to each element on array `self` in order to + /// return an array the same size as `self` or the first error encountered. + /// + /// The return type of this function depends on the return type of the closure. + /// If you return `Result<T, E>` from the closure, you'll get a `Result<[T; N]; E>`. + /// If you return `Option<T>` from the closure, you'll get an `Option<[T; N]>`. + /// + /// # Examples + /// + /// ``` + /// #![feature(array_try_map)] + /// let a = ["1", "2", "3"]; + /// let b = a.try_map(|v| v.parse::<u32>()).unwrap().map(|v| v + 1); + /// assert_eq!(b, [2, 3, 4]); + /// + /// let a = ["1", "2a", "3"]; + /// let b = a.try_map(|v| v.parse::<u32>()); + /// assert!(b.is_err()); + /// + /// use std::num::NonZeroU32; + /// let z = [1, 2, 0, 3, 4]; + /// assert_eq!(z.try_map(NonZeroU32::new), None); + /// let a = [1, 2, 3]; + /// let b = a.try_map(NonZeroU32::new); + /// let c = b.map(|x| x.map(NonZeroU32::get)); + /// assert_eq!(c, Some(a)); + /// ``` + #[unstable(feature = "array_try_map", issue = "79711")] + pub fn try_map<F, R>(self, f: F) -> ChangeOutputType<R, [R::Output; N]> + where + F: FnMut(T) -> R, + R: Try, + R::Residual: Residual<[R::Output; N]>, + { + // SAFETY: we know for certain that this iterator will yield exactly `N` + // items. + unsafe { try_collect_into_array_unchecked(&mut IntoIterator::into_iter(self).map(f)) } + } + + /// 'Zips up' two arrays into a single array of pairs. + /// + /// `zip()` returns a new array where every element is a tuple where the + /// first element comes from the first array, and the second element comes + /// from the second array. In other words, it zips two arrays together, + /// into a single one. + /// + /// # Examples + /// + /// ``` + /// #![feature(array_zip)] + /// let x = [1, 2, 3]; + /// let y = [4, 5, 6]; + /// let z = x.zip(y); + /// assert_eq!(z, [(1, 4), (2, 5), (3, 6)]); + /// ``` + #[unstable(feature = "array_zip", issue = "80094")] + pub fn zip<U>(self, rhs: [U; N]) -> [(T, U); N] { + let mut iter = IntoIterator::into_iter(self).zip(rhs); + + // SAFETY: we know for certain that this iterator will yield exactly `N` + // items. + unsafe { collect_into_array_unchecked(&mut iter) } + } + + /// Returns a slice containing the entire array. Equivalent to `&s[..]`. + #[stable(feature = "array_as_slice", since = "1.57.0")] + #[rustc_const_stable(feature = "array_as_slice", since = "1.57.0")] + pub const fn as_slice(&self) -> &[T] { + self + } + + /// Returns a mutable slice containing the entire array. Equivalent to + /// `&mut s[..]`. + #[stable(feature = "array_as_slice", since = "1.57.0")] + pub fn as_mut_slice(&mut self) -> &mut [T] { + self + } + + /// Borrows each element and returns an array of references with the same + /// size as `self`. + /// + /// + /// # Example + /// + /// ``` + /// #![feature(array_methods)] + /// + /// let floats = [3.1, 2.7, -1.0]; + /// let float_refs: [&f64; 3] = floats.each_ref(); + /// assert_eq!(float_refs, [&3.1, &2.7, &-1.0]); + /// ``` + /// + /// This method is particularly useful if combined with other methods, like + /// [`map`](#method.map). This way, you can avoid moving the original + /// array if its elements are not [`Copy`]. + /// + /// ``` + /// #![feature(array_methods)] + /// + /// let strings = ["Ferris".to_string(), "♥".to_string(), "Rust".to_string()]; + /// let is_ascii = strings.each_ref().map(|s| s.is_ascii()); + /// assert_eq!(is_ascii, [true, false, true]); + /// + /// // We can still access the original array: it has not been moved. + /// assert_eq!(strings.len(), 3); + /// ``` + #[unstable(feature = "array_methods", issue = "76118")] + pub fn each_ref(&self) -> [&T; N] { + // SAFETY: we know for certain that this iterator will yield exactly `N` + // items. + unsafe { collect_into_array_unchecked(&mut self.iter()) } + } + + /// Borrows each element mutably and returns an array of mutable references + /// with the same size as `self`. + /// + /// + /// # Example + /// + /// ``` + /// #![feature(array_methods)] + /// + /// let mut floats = [3.1, 2.7, -1.0]; + /// let float_refs: [&mut f64; 3] = floats.each_mut(); + /// *float_refs[0] = 0.0; + /// assert_eq!(float_refs, [&mut 0.0, &mut 2.7, &mut -1.0]); + /// assert_eq!(floats, [0.0, 2.7, -1.0]); + /// ``` + #[unstable(feature = "array_methods", issue = "76118")] + pub fn each_mut(&mut self) -> [&mut T; N] { + // SAFETY: we know for certain that this iterator will yield exactly `N` + // items. + unsafe { collect_into_array_unchecked(&mut self.iter_mut()) } + } + + /// Divides one array reference into two at an index. + /// + /// The first will contain all indices from `[0, M)` (excluding + /// the index `M` itself) and the second will contain all + /// indices from `[M, N)` (excluding the index `N` itself). + /// + /// # Panics + /// + /// Panics if `M > N`. + /// + /// # Examples + /// + /// ``` + /// #![feature(split_array)] + /// + /// let v = [1, 2, 3, 4, 5, 6]; + /// + /// { + /// let (left, right) = v.split_array_ref::<0>(); + /// assert_eq!(left, &[]); + /// assert_eq!(right, &[1, 2, 3, 4, 5, 6]); + /// } + /// + /// { + /// let (left, right) = v.split_array_ref::<2>(); + /// assert_eq!(left, &[1, 2]); + /// assert_eq!(right, &[3, 4, 5, 6]); + /// } + /// + /// { + /// let (left, right) = v.split_array_ref::<6>(); + /// assert_eq!(left, &[1, 2, 3, 4, 5, 6]); + /// assert_eq!(right, &[]); + /// } + /// ``` + #[unstable( + feature = "split_array", + reason = "return type should have array as 2nd element", + issue = "90091" + )] + #[inline] + pub fn split_array_ref<const M: usize>(&self) -> (&[T; M], &[T]) { + (&self[..]).split_array_ref::<M>() + } + + /// Divides one mutable array reference into two at an index. + /// + /// The first will contain all indices from `[0, M)` (excluding + /// the index `M` itself) and the second will contain all + /// indices from `[M, N)` (excluding the index `N` itself). + /// + /// # Panics + /// + /// Panics if `M > N`. + /// + /// # Examples + /// + /// ``` + /// #![feature(split_array)] + /// + /// let mut v = [1, 0, 3, 0, 5, 6]; + /// let (left, right) = v.split_array_mut::<2>(); + /// assert_eq!(left, &mut [1, 0][..]); + /// assert_eq!(right, &mut [3, 0, 5, 6]); + /// left[1] = 2; + /// right[1] = 4; + /// assert_eq!(v, [1, 2, 3, 4, 5, 6]); + /// ``` + #[unstable( + feature = "split_array", + reason = "return type should have array as 2nd element", + issue = "90091" + )] + #[inline] + pub fn split_array_mut<const M: usize>(&mut self) -> (&mut [T; M], &mut [T]) { + (&mut self[..]).split_array_mut::<M>() + } + + /// Divides one array reference into two at an index from the end. + /// + /// The first will contain all indices from `[0, N - M)` (excluding + /// the index `N - M` itself) and the second will contain all + /// indices from `[N - M, N)` (excluding the index `N` itself). + /// + /// # Panics + /// + /// Panics if `M > N`. + /// + /// # Examples + /// + /// ``` + /// #![feature(split_array)] + /// + /// let v = [1, 2, 3, 4, 5, 6]; + /// + /// { + /// let (left, right) = v.rsplit_array_ref::<0>(); + /// assert_eq!(left, &[1, 2, 3, 4, 5, 6]); + /// assert_eq!(right, &[]); + /// } + /// + /// { + /// let (left, right) = v.rsplit_array_ref::<2>(); + /// assert_eq!(left, &[1, 2, 3, 4]); + /// assert_eq!(right, &[5, 6]); + /// } + /// + /// { + /// let (left, right) = v.rsplit_array_ref::<6>(); + /// assert_eq!(left, &[]); + /// assert_eq!(right, &[1, 2, 3, 4, 5, 6]); + /// } + /// ``` + #[unstable( + feature = "split_array", + reason = "return type should have array as 2nd element", + issue = "90091" + )] + #[inline] + pub fn rsplit_array_ref<const M: usize>(&self) -> (&[T], &[T; M]) { + (&self[..]).rsplit_array_ref::<M>() + } + + /// Divides one mutable array reference into two at an index from the end. + /// + /// The first will contain all indices from `[0, N - M)` (excluding + /// the index `N - M` itself) and the second will contain all + /// indices from `[N - M, N)` (excluding the index `N` itself). + /// + /// # Panics + /// + /// Panics if `M > N`. + /// + /// # Examples + /// + /// ``` + /// #![feature(split_array)] + /// + /// let mut v = [1, 0, 3, 0, 5, 6]; + /// let (left, right) = v.rsplit_array_mut::<4>(); + /// assert_eq!(left, &mut [1, 0]); + /// assert_eq!(right, &mut [3, 0, 5, 6][..]); + /// left[1] = 2; + /// right[1] = 4; + /// assert_eq!(v, [1, 2, 3, 4, 5, 6]); + /// ``` + #[unstable( + feature = "split_array", + reason = "return type should have array as 2nd element", + issue = "90091" + )] + #[inline] + pub fn rsplit_array_mut<const M: usize>(&mut self) -> (&mut [T], &mut [T; M]) { + (&mut self[..]).rsplit_array_mut::<M>() + } +} + +/// Pulls `N` items from `iter` and returns them as an array. If the iterator +/// yields fewer than `N` items, this function exhibits undefined behavior. +/// +/// See [`try_collect_into_array`] for more information. +/// +/// +/// # Safety +/// +/// It is up to the caller to guarantee that `iter` yields at least `N` items. +/// Violating this condition causes undefined behavior. +unsafe fn try_collect_into_array_unchecked<I, T, R, const N: usize>(iter: &mut I) -> R::TryType +where + // Note: `TrustedLen` here is somewhat of an experiment. This is just an + // internal function, so feel free to remove if this bound turns out to be a + // bad idea. In that case, remember to also remove the lower bound + // `debug_assert!` below! + I: Iterator + TrustedLen, + I::Item: Try<Output = T, Residual = R>, + R: Residual<[T; N]>, +{ + debug_assert!(N <= iter.size_hint().1.unwrap_or(usize::MAX)); + debug_assert!(N <= iter.size_hint().0); + + // SAFETY: covered by the function contract. + unsafe { try_collect_into_array(iter).unwrap_unchecked() } +} + +// Infallible version of `try_collect_into_array_unchecked`. +unsafe fn collect_into_array_unchecked<I, const N: usize>(iter: &mut I) -> [I::Item; N] +where + I: Iterator + TrustedLen, +{ + let mut map = iter.map(NeverShortCircuit); + + // SAFETY: The same safety considerations w.r.t. the iterator length + // apply for `try_collect_into_array_unchecked` as for + // `collect_into_array_unchecked` + match unsafe { try_collect_into_array_unchecked(&mut map) } { + NeverShortCircuit(array) => array, + } +} + +/// Pulls `N` items from `iter` and returns them as an array. If the iterator +/// yields fewer than `N` items, `Err` is returned containing an iterator over +/// the already yielded items. +/// +/// Since the iterator is passed as a mutable reference and this function calls +/// `next` at most `N` times, the iterator can still be used afterwards to +/// retrieve the remaining items. +/// +/// If `iter.next()` panicks, all items already yielded by the iterator are +/// dropped. +#[inline] +fn try_collect_into_array<I, T, R, const N: usize>( + iter: &mut I, +) -> Result<R::TryType, IntoIter<T, N>> +where + I: Iterator, + I::Item: Try<Output = T, Residual = R>, + R: Residual<[T; N]>, +{ + if N == 0 { + // SAFETY: An empty array is always inhabited and has no validity invariants. + return Ok(Try::from_output(unsafe { mem::zeroed() })); + } + + struct Guard<'a, T, const N: usize> { + array_mut: &'a mut [MaybeUninit<T>; N], + initialized: usize, + } + + impl<T, const N: usize> Drop for Guard<'_, T, N> { + fn drop(&mut self) { + debug_assert!(self.initialized <= N); + + // SAFETY: this slice will contain only initialized objects. + unsafe { + crate::ptr::drop_in_place(MaybeUninit::slice_assume_init_mut( + &mut self.array_mut.get_unchecked_mut(..self.initialized), + )); + } + } + } + + let mut array = MaybeUninit::uninit_array::<N>(); + let mut guard = Guard { array_mut: &mut array, initialized: 0 }; + + for _ in 0..N { + match iter.next() { + Some(item_rslt) => { + let item = match item_rslt.branch() { + ControlFlow::Break(r) => { + return Ok(FromResidual::from_residual(r)); + } + ControlFlow::Continue(elem) => elem, + }; + + // SAFETY: `guard.initialized` starts at 0, is increased by one in the + // loop and the loop is aborted once it reaches N (which is + // `array.len()`). + unsafe { + guard.array_mut.get_unchecked_mut(guard.initialized).write(item); + } + guard.initialized += 1; + } + None => { + let alive = 0..guard.initialized; + mem::forget(guard); + // SAFETY: `array` was initialized with exactly `initialized` + // number of elements. + return Err(unsafe { IntoIter::new_unchecked(array, alive) }); + } + } + } + + mem::forget(guard); + // SAFETY: All elements of the array were populated in the loop above. + let output = unsafe { MaybeUninit::array_assume_init(array) }; + Ok(Try::from_output(output)) +} + +/// Returns the next chunk of `N` items from the iterator or errors with an +/// iterator over the remainder. Used for `Iterator::next_chunk`. +#[inline] +pub(crate) fn iter_next_chunk<I, const N: usize>( + iter: &mut I, +) -> Result<[I::Item; N], IntoIter<I::Item, N>> +where + I: Iterator, +{ + let mut map = iter.map(NeverShortCircuit); + try_collect_into_array(&mut map).map(|NeverShortCircuit(arr)| arr) +} |