From f0f9d88de6b74592a9fb2bb67c9a3c64edfcb54c Mon Sep 17 00:00:00 2001 From: Frank King Date: Wed, 10 May 2023 17:08:28 +0800 Subject: [PATCH] Add Iterator::map_windows This is inherited from the old PR This method returns an iterator over mapped windows of the starting iterator. Adding the more straight-forward `Iterator::windows` is not easily possible right now as the items are stored in the iterator type, meaning the `next` call would return references to `self`. This is not allowed by the current `Iterator` trait design. This might change once GATs have landed. The idea has been brought up by @m-ou-se here: https://rust-lang.zulipchat.com/#narrow/stream/219381-t-libs/topic/Iterator.3A.3A.7Bpairwise.2C.20windows.7D/near/224587771 Co-authored-by: Lukas Kalbertodt --- library/core/src/iter/adapters/map_windows.rs | 293 ++++++++++++++++++ library/core/src/iter/adapters/mod.rs | 4 + library/core/src/iter/mod.rs | 2 + library/core/src/iter/traits/iterator.rs | 160 +++++++++- .../core/tests/iter/adapters/map_windows.rs | 279 +++++++++++++++++ library/core/tests/iter/adapters/mod.rs | 1 + library/core/tests/lib.rs | 1 + 7 files changed, 739 insertions(+), 1 deletion(-) create mode 100644 library/core/src/iter/adapters/map_windows.rs create mode 100644 library/core/tests/iter/adapters/map_windows.rs diff --git a/library/core/src/iter/adapters/map_windows.rs b/library/core/src/iter/adapters/map_windows.rs new file mode 100644 index 0000000000000..3c0e80b2559db --- /dev/null +++ b/library/core/src/iter/adapters/map_windows.rs @@ -0,0 +1,293 @@ +use crate::{ + fmt, + iter::{ExactSizeIterator, FusedIterator}, + mem::{self, MaybeUninit}, + ptr, +}; + +/// An iterator over the mapped windows of another iterator. +/// +/// This `struct` is created by the [`Iterator::map_windows`]. See its +/// documentation for more information. +#[must_use = "iterators are lazy and do nothing unless consumed"] +#[unstable(feature = "iter_map_windows", reason = "recently added", issue = "87155")] +pub struct MapWindows { + f: F, + inner: MapWindowsInner, +} + +struct MapWindowsInner { + // We fuse the inner iterator because there shouldn't be "holes" in + // the sliding window. Once the iterator returns a `None`, we make + // our `MapWindows` iterator return `None` forever. + iter: Option, + // Since iterators are assumed lazy, i.e. it only yields an item when + // `Iterator::next()` is called, and `MapWindows` is not an exception. + // + // Before the first iteration, we keep the buffer `None`. When the user + // first call `next` or other methods that makes the iterator advance, + // we collect the first `N` items yielded from the inner iterator and + // put it into the buffer. + // + // When the inner iterator has returned a `None` (i.e. fused), we take + // away this `buffer` and leave it `None` to reclaim its resources. + // + // FIXME: should we shrink the size of `buffer` using niche optimization? + buffer: Option>, +} + +// `Buffer` uses two times of space to reduce moves among the iterations. +// `Buffer` is semantically `[MaybeUninit; 2 * N]`. However, due +// to limitations of const generics, we use this different type. Note that +// it has the same underlying memory layout. +struct Buffer { + // Invariant: `self.buffer[self.start..self.start + N]` is initialized, + // with all other elements being uninitialized. This also + // implies that `self.start <= N`. + buffer: [[MaybeUninit; N]; 2], + start: usize, +} + +impl MapWindows { + pub(in crate::iter) fn new(iter: I, f: F) -> Self { + assert!(N != 0, "array in `Iterator::map_windows` must contain more than 0 elements"); + + // Only ZST arrays' length can be so large. + if mem::size_of::() == 0 { + assert!( + N.checked_mul(2).is_some(), + "array size of `Iterator::map_windows` is too large" + ); + } + + Self { inner: MapWindowsInner::new(iter), f } + } +} + +impl MapWindowsInner { + #[inline] + fn new(iter: I) -> Self { + Self { iter: Some(iter), buffer: None } + } + + fn next_window(&mut self) -> Option<&[I::Item; N]> { + let iter = self.iter.as_mut()?; + match self.buffer { + // It is the first time to advance. We collect + // the first `N` items from `self.iter` to initialize `self.buffer`. + None => self.buffer = Buffer::try_from_iter(iter), + Some(ref mut buffer) => match iter.next() { + None => { + // Fuse the inner iterator since it yields a `None`. + self.iter.take(); + self.buffer.take(); + } + // Advance the iterator. We first call `next` before changing our buffer + // at all. This means that if `next` panics, our invariant is upheld and + // our `Drop` impl drops the correct elements. + Some(item) => buffer.push(item), + }, + } + self.buffer.as_ref().map(Buffer::as_array_ref) + } + + fn size_hint(&self) -> (usize, Option) { + let Some(ref iter) = self.iter else { return (0, Some(0)) }; + let (lo, hi) = iter.size_hint(); + if self.buffer.is_some() { + // If the first `N` items are already yielded by the inner iterator, + // the size hint is then equal to the that of the inner iterator's. + (lo, hi) + } else { + // If the first `N` items are not yet yielded by the inner iterator, + // the first `N` elements should be counted as one window, so both bounds + // should subtract `N - 1`. + (lo.saturating_sub(N - 1), hi.map(|hi| hi.saturating_sub(N - 1))) + } + } +} + +impl Buffer { + fn try_from_iter(iter: &mut impl Iterator) -> Option { + let first_half = crate::array::iter_next_chunk(iter).ok()?; + let buffer = [MaybeUninit::new(first_half).transpose(), MaybeUninit::uninit_array()]; + Some(Self { buffer, start: 0 }) + } + + #[inline] + fn buffer_ptr(&self) -> *const MaybeUninit { + self.buffer.as_ptr().cast() + } + + #[inline] + fn buffer_mut_ptr(&mut self) -> *mut MaybeUninit { + self.buffer.as_mut_ptr().cast() + } + + #[inline] + fn as_array_ref(&self) -> &[T; N] { + debug_assert!(self.start + N <= 2 * N); + + // SAFETY: our invariant guarantees these elements are initialized. + unsafe { &*self.buffer_ptr().add(self.start).cast() } + } + + #[inline] + fn as_uninit_array_mut(&mut self) -> &mut MaybeUninit<[T; N]> { + debug_assert!(self.start + N <= 2 * N); + + // SAFETY: our invariant guarantees these elements are in bounds. + unsafe { &mut *self.buffer_mut_ptr().add(self.start).cast() } + } + + /// Pushes a new item `next` to the back, and pops the front-most one. + /// + /// All the elements will be shifted to the front end when pushing reaches + /// the back end. + fn push(&mut self, next: T) { + let buffer_mut_ptr = self.buffer_mut_ptr(); + debug_assert!(self.start + N <= 2 * N); + + let to_drop = if self.start == N { + // We have reached the end of our buffer and have to copy + // everything to the start. Example layout for N = 3. + // + // 0 1 2 3 4 5 0 1 2 3 4 5 + // ┌───┬───┬───┬───┬───┬───┐ ┌───┬───┬───┬───┬───┬───┐ + // │ - │ - │ - │ a │ b │ c │ -> │ b │ c │ n │ - │ - │ - │ + // └───┴───┴───┴───┴───┴───┘ └───┴───┴───┴───┴───┴───┘ + // ↑ ↑ + // start start + + // SAFETY: the two pointers are valid for reads/writes of N -1 + // elements because our array's size is semantically 2 * N. The + // regions also don't overlap for the same reason. + // + // We leave the old elements in place. As soon as `start` is set + // to 0, we treat them as uninitialized and treat their copies + // as initialized. + let to_drop = unsafe { + ptr::copy_nonoverlapping(buffer_mut_ptr.add(self.start + 1), buffer_mut_ptr, N - 1); + (*buffer_mut_ptr.add(N - 1)).write(next); + buffer_mut_ptr.add(self.start) + }; + self.start = 0; + to_drop + } else { + // SAFETY: `self.start` is < N as guaranteed by the invariant + // plus the check above. Even if the drop at the end panics, + // the invariant is upheld. + // + // Example layout for N = 3: + // + // 0 1 2 3 4 5 0 1 2 3 4 5 + // ┌───┬───┬───┬───┬───┬───┐ ┌───┬───┬───┬───┬───┬───┐ + // │ - │ a │ b │ c │ - │ - │ -> │ - │ - │ b │ c │ n │ - │ + // └───┴───┴───┴───┴───┴───┘ └───┴───┴───┴───┴───┴───┘ + // ↑ ↑ + // start start + // + let to_drop = unsafe { + (*buffer_mut_ptr.add(self.start + N)).write(next); + buffer_mut_ptr.add(self.start) + }; + self.start += 1; + to_drop + }; + + // SAFETY: the index is valid and this is element `a` in the + // diagram above and has not been dropped yet. + unsafe { ptr::drop_in_place(to_drop.cast::()) }; + } +} + +impl Clone for Buffer { + fn clone(&self) -> Self { + let mut buffer = Buffer { + buffer: [MaybeUninit::uninit_array(), MaybeUninit::uninit_array()], + start: self.start, + }; + buffer.as_uninit_array_mut().write(self.as_array_ref().clone()); + buffer + } +} + +impl Clone for MapWindowsInner +where + I: Iterator + Clone, + I::Item: Clone, +{ + fn clone(&self) -> Self { + Self { iter: self.iter.clone(), buffer: self.buffer.clone() } + } +} + +impl Drop for Buffer { + fn drop(&mut self) { + // SAFETY: our invariant guarantees that N elements starting from + // `self.start` are initialized. We drop them here. + unsafe { + let initialized_part: *mut [T] = crate::ptr::slice_from_raw_parts_mut( + self.buffer_mut_ptr().add(self.start).cast(), + N, + ); + ptr::drop_in_place(initialized_part); + } + } +} + +#[unstable(feature = "iter_map_windows", reason = "recently added", issue = "87155")] +impl Iterator for MapWindows +where + I: Iterator, + F: FnMut(&[I::Item; N]) -> R, +{ + type Item = R; + + fn next(&mut self) -> Option { + let window = self.inner.next_window()?; + let out = (self.f)(window); + Some(out) + } + + fn size_hint(&self) -> (usize, Option) { + self.inner.size_hint() + } +} + +// Note that even if the inner iterator not fused, the `MapWindows` is still fused, +// because we don't allow "holes" in the mapping window. +#[unstable(feature = "iter_map_windows", reason = "recently added", issue = "87155")] +impl FusedIterator for MapWindows +where + I: Iterator, + F: FnMut(&[I::Item; N]) -> R, +{ +} + +#[unstable(feature = "iter_map_windows", reason = "recently added", issue = "87155")] +impl ExactSizeIterator for MapWindows +where + I: ExactSizeIterator, + F: FnMut(&[I::Item; N]) -> R, +{ +} + +#[unstable(feature = "iter_map_windows", reason = "recently added", issue = "87155")] +impl fmt::Debug for MapWindows { + fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { + f.debug_struct("MapWindows").field("iter", &self.inner.iter).finish() + } +} + +#[unstable(feature = "iter_map_windows", reason = "recently added", issue = "87155")] +impl Clone for MapWindows +where + I: Iterator + Clone, + F: Clone, + I::Item: Clone, +{ + fn clone(&self) -> Self { + Self { f: self.f.clone(), inner: self.inner.clone() } + } +} diff --git a/library/core/src/iter/adapters/mod.rs b/library/core/src/iter/adapters/mod.rs index 8cc2b7cec4165..6f4fa7010f446 100644 --- a/library/core/src/iter/adapters/mod.rs +++ b/library/core/src/iter/adapters/mod.rs @@ -16,6 +16,7 @@ mod inspect; mod intersperse; mod map; mod map_while; +mod map_windows; mod peekable; mod rev; mod scan; @@ -57,6 +58,9 @@ pub use self::intersperse::{Intersperse, IntersperseWith}; #[stable(feature = "iter_map_while", since = "1.57.0")] pub use self::map_while::MapWhile; +#[unstable(feature = "iter_map_windows", reason = "recently added", issue = "87155")] +pub use self::map_windows::MapWindows; + #[unstable(feature = "trusted_random_access", issue = "none")] pub use self::zip::TrustedRandomAccess; diff --git a/library/core/src/iter/mod.rs b/library/core/src/iter/mod.rs index de638552fa378..424504ebd0a5e 100644 --- a/library/core/src/iter/mod.rs +++ b/library/core/src/iter/mod.rs @@ -434,6 +434,8 @@ pub use self::adapters::Copied; pub use self::adapters::Flatten; #[stable(feature = "iter_map_while", since = "1.57.0")] pub use self::adapters::MapWhile; +#[unstable(feature = "iter_map_windows", reason = "recently added", issue = "87155")] +pub use self::adapters::MapWindows; #[unstable(feature = "inplace_iteration", issue = "none")] pub use self::adapters::SourceIter; #[stable(feature = "iterator_step_by", since = "1.28.0")] diff --git a/library/core/src/iter/traits/iterator.rs b/library/core/src/iter/traits/iterator.rs index dabfce1447483..0eac0e3eb699b 100644 --- a/library/core/src/iter/traits/iterator.rs +++ b/library/core/src/iter/traits/iterator.rs @@ -10,7 +10,8 @@ use super::super::{ArrayChunks, Chain, Cloned, Copied, Cycle, Enumerate, Filter, use super::super::{FlatMap, Flatten}; use super::super::{FromIterator, Intersperse, IntersperseWith, Product, Sum, Zip}; use super::super::{ - Inspect, Map, MapWhile, Peekable, Rev, Scan, Skip, SkipWhile, StepBy, Take, TakeWhile, + Inspect, Map, MapWhile, MapWindows, Peekable, Rev, Scan, Skip, SkipWhile, StepBy, Take, + TakeWhile, }; fn _assert_is_object_safe(_: &dyn Iterator) {} @@ -1591,6 +1592,163 @@ pub trait Iterator { Flatten::new(self) } + /// Calls the given function `f` for each contiguous window of size `N` over + /// `self` and returns an iterator over the outputs of `f`. Like [`slice::windows()`], + /// the windows during mapping overlap as well. + /// + /// In the following example, the closure is called three times with the + /// arguments `&['a', 'b']`, `&['b', 'c']` and `&['c', 'd']` respectively. + /// + /// ``` + /// #![feature(iter_map_windows)] + /// + /// let strings = "abcd".chars() + /// .map_windows(|[x, y]| format!("{}+{}", x, y)) + /// .collect::>(); + /// + /// assert_eq!(strings, vec!["a+b", "b+c", "c+d"]); + /// ``` + /// + /// Note that the const parameter `N` is usually inferred by the + /// destructured argument in the closure. + /// + /// The returned iterator yields 𝑘 − `N` + 1 items (where 𝑘 is the number of + /// items yielded by `self`). If 𝑘 is less than `N`, this method yields an + /// empty iterator. + /// + /// The returned iterator implements [`FusedIterator`], because once `self` + /// returns `None`, even if it returns a `Some(T)` again in the next iterations, + /// we cannot put it into a contigious array buffer, and thus the returned iterator + /// should be fused. + /// + /// [`slice::windows()`]: slice::windows + /// [`FusedIterator`]: crate::iter::FusedIterator + /// + /// # Panics + /// + /// Panics if `N` is 0. This check will most probably get changed to a + /// compile time error before this method gets stabilized. + /// + /// ```should_panic + /// #![feature(iter_map_windows)] + /// + /// let iter = std::iter::repeat(0).map_windows(|&[]| ()); + /// ``` + /// + /// # Examples + /// + /// Building the sums of neighboring numbers. + /// + /// ``` + /// #![feature(iter_map_windows)] + /// + /// let mut it = [1, 3, 8, 1].iter().map_windows(|&[a, b]| a + b); + /// assert_eq!(it.next(), Some(4)); // 1 + 3 + /// assert_eq!(it.next(), Some(11)); // 3 + 8 + /// assert_eq!(it.next(), Some(9)); // 8 + 1 + /// assert_eq!(it.next(), None); + /// ``` + /// + /// Since the elements in the following example implement `Copy`, we can + /// just copy the array and get an iterator over the windows. + /// + /// ``` + /// #![feature(iter_map_windows)] + /// + /// let mut it = "ferris".chars().map_windows(|w: &[_; 3]| *w); + /// assert_eq!(it.next(), Some(['f', 'e', 'r'])); + /// assert_eq!(it.next(), Some(['e', 'r', 'r'])); + /// assert_eq!(it.next(), Some(['r', 'r', 'i'])); + /// assert_eq!(it.next(), Some(['r', 'i', 's'])); + /// assert_eq!(it.next(), None); + /// ``` + /// + /// You can also use this function to check the sortedness of an iterator. + /// For the simple case, rather use [`Iterator::is_sorted`]. + /// + /// ``` + /// #![feature(iter_map_windows)] + /// + /// let mut it = [0.5, 1.0, 3.5, 3.0, 8.5, 8.5, f32::NAN].iter() + /// .map_windows(|[a, b]| a <= b); + /// + /// assert_eq!(it.next(), Some(true)); // 0.5 <= 1.0 + /// assert_eq!(it.next(), Some(true)); // 1.0 <= 3.5 + /// assert_eq!(it.next(), Some(false)); // 3.5 <= 3.0 + /// assert_eq!(it.next(), Some(true)); // 3.0 <= 8.5 + /// assert_eq!(it.next(), Some(true)); // 8.5 <= 8.5 + /// assert_eq!(it.next(), Some(false)); // 8.5 <= NAN + /// assert_eq!(it.next(), None); + /// ``` + /// + /// For non-fused iterators, they are fused after `map_windows`. + /// + /// ``` + /// #![feature(iter_map_windows)] + /// + /// #[derive(Default)] + /// struct NonFusedIterator { + /// state: i32, + /// } + /// + /// impl Iterator for NonFusedIterator { + /// type Item = i32; + /// + /// fn next(&mut self) -> Option { + /// let val = self.state; + /// self.state = self.state + 1; + /// + /// // yields `0..5` first, then only even numbers since `6..`. + /// if val < 5 || val % 2 == 0 { + /// Some(val) + /// } else { + /// None + /// } + /// } + /// } + /// + /// + /// let mut iter = NonFusedIterator::default(); + /// + /// // yields 0..5 first. + /// assert_eq!(iter.next(), Some(0)); + /// assert_eq!(iter.next(), Some(1)); + /// assert_eq!(iter.next(), Some(2)); + /// assert_eq!(iter.next(), Some(3)); + /// assert_eq!(iter.next(), Some(4)); + /// // then we can see our iterator going back and forth + /// assert_eq!(iter.next(), None); + /// assert_eq!(iter.next(), Some(6)); + /// assert_eq!(iter.next(), None); + /// assert_eq!(iter.next(), Some(8)); + /// assert_eq!(iter.next(), None); + /// + /// // however, with `.map_windows()`, it is fused. + /// let mut iter = NonFusedIterator::default() + /// .map_windows(|arr: &[_; 2]| *arr); + /// + /// assert_eq!(iter.next(), Some([0, 1])); + /// assert_eq!(iter.next(), Some([1, 2])); + /// assert_eq!(iter.next(), Some([2, 3])); + /// assert_eq!(iter.next(), Some([3, 4])); + /// assert_eq!(iter.next(), None); + /// + /// // it will always return `None` after the first time. + /// assert_eq!(iter.next(), None); + /// assert_eq!(iter.next(), None); + /// assert_eq!(iter.next(), None); + /// ``` + #[inline] + #[unstable(feature = "iter_map_windows", reason = "recently added", issue = "87155")] + #[rustc_do_not_const_check] + fn map_windows(self, f: F) -> MapWindows + where + Self: Sized, + F: FnMut(&[Self::Item; N]) -> R, + { + MapWindows::new(self, f) + } + /// Creates an iterator which ends after the first [`None`]. /// /// After an iterator returns [`None`], future calls may or may not yield diff --git a/library/core/tests/iter/adapters/map_windows.rs b/library/core/tests/iter/adapters/map_windows.rs new file mode 100644 index 0000000000000..47f12b28be0ba --- /dev/null +++ b/library/core/tests/iter/adapters/map_windows.rs @@ -0,0 +1,279 @@ +//! These tests mainly make sure the elements are correctly dropped. + +use std::sync::atomic::{AtomicBool, AtomicUsize, Ordering::SeqCst}; + +#[derive(Debug)] +struct DropInfo { + dropped_twice: AtomicBool, + alive_count: AtomicUsize, +} + +impl DropInfo { + const fn new() -> Self { + Self { dropped_twice: AtomicBool::new(false), alive_count: AtomicUsize::new(0) } + } + + #[track_caller] + fn check(&self) { + assert!(!self.dropped_twice.load(SeqCst), "a value was dropped twice"); + assert_eq!(self.alive_count.load(SeqCst), 0); + } +} + +#[derive(Debug)] +struct DropCheck<'a> { + info: &'a DropInfo, + was_dropped: bool, +} + +impl<'a> DropCheck<'a> { + fn new(info: &'a DropInfo) -> Self { + info.alive_count.fetch_add(1, SeqCst); + + Self { info, was_dropped: false } + } +} + +impl Drop for DropCheck<'_> { + fn drop(&mut self) { + if self.was_dropped { + self.info.dropped_twice.store(true, SeqCst); + } + self.was_dropped = true; + + self.info.alive_count.fetch_sub(1, SeqCst); + } +} + +fn iter(info: &DropInfo, len: usize, panic_at: usize) -> impl Iterator> { + (0..len).map(move |i| { + if i == panic_at { + panic!("intended panic"); + } + DropCheck::new(info) + }) +} + +#[track_caller] +fn check(len: usize, panic_at: usize) { + check_drops(|info| { + iter(info, len, panic_at).map_windows(|_: &[_; N]| {}).last(); + }); +} + +#[track_caller] +fn check_drops(f: impl FnOnce(&DropInfo)) { + let info = DropInfo::new(); + let _ = std::panic::catch_unwind(std::panic::AssertUnwindSafe(|| { + f(&info); + })); + info.check(); +} + +#[test] +fn drop_check_no_iter_panic_n1() { + check::<1>(0, 100); + check::<1>(1, 100); + check::<1>(2, 100); + check::<1>(13, 100); +} + +#[test] +fn drop_check_no_iter_panic_n2() { + check::<2>(0, 100); + check::<2>(1, 100); + check::<2>(2, 100); + check::<2>(3, 100); + check::<2>(13, 100); +} + +#[test] +fn drop_check_no_iter_panic_n5() { + check::<5>(0, 100); + check::<5>(1, 100); + check::<5>(2, 100); + check::<5>(13, 100); + check::<5>(30, 100); +} + +#[test] +fn drop_check_panic_in_first_batch() { + check::<1>(7, 0); + + check::<2>(7, 0); + check::<2>(7, 1); + + check::<3>(7, 0); + check::<3>(7, 1); + check::<3>(7, 2); +} + +#[test] +fn drop_check_panic_in_middle() { + check::<1>(7, 1); + check::<1>(7, 5); + check::<1>(7, 6); + + check::<2>(7, 2); + check::<2>(7, 5); + check::<2>(7, 6); + + check::<5>(13, 5); + check::<5>(13, 8); + check::<5>(13, 12); +} + +#[test] +fn drop_check_len_equals_n() { + check::<1>(1, 100); + check::<1>(1, 0); + + check::<2>(2, 100); + check::<2>(2, 0); + check::<2>(2, 1); + + check::<5>(5, 100); + check::<5>(5, 0); + check::<5>(5, 1); + check::<5>(5, 4); +} + +#[test] +fn output_n1() { + assert_eq!("".chars().map_windows(|[c]| *c).collect::>(), vec![]); + assert_eq!("x".chars().map_windows(|[c]| *c).collect::>(), vec!['x']); + assert_eq!("abcd".chars().map_windows(|[c]| *c).collect::>(), vec!['a', 'b', 'c', 'd']); +} + +#[test] +fn output_n2() { + assert_eq!( + "".chars().map_windows(|a: &[_; 2]| *a).collect::>(), + >::new(), + ); + assert_eq!("ab".chars().map_windows(|a: &[_; 2]| *a).collect::>(), vec![['a', 'b']]); + assert_eq!( + "abcd".chars().map_windows(|a: &[_; 2]| *a).collect::>(), + vec![['a', 'b'], ['b', 'c'], ['c', 'd']], + ); +} + +#[test] +fn test_case_from_pr_82413_comment() { + for () in std::iter::repeat("0".to_owned()).map_windows(|_: &[_; 3]| {}).take(4) {} +} + +#[test] +#[should_panic = "array in `Iterator::map_windows` must contain more than 0 elements"] +fn check_zero_window() { + let _ = std::iter::repeat(0).map_windows(|_: &[_; 0]| ()); +} + +#[test] +fn test_zero_sized_type() { + #[derive(Copy, Clone, Debug, Eq, PartialEq)] + struct Data; + let data: Vec<_> = + std::iter::repeat(Data).take(10).map_windows(|arr: &[Data; 5]| *arr).collect(); + assert_eq!(data, [[Data; 5]; 6]); +} + +#[test] +#[should_panic = "array size of `Iterator::map_windows` is too large"] +fn test_too_large_array_size() { + let _ = std::iter::repeat(()).map_windows(|arr: &[(); usize::MAX]| *arr); +} + +#[test] +fn test_laziness() { + let counter = AtomicUsize::new(0); + let mut iter = (0..5) + .inspect(|_| { + counter.fetch_add(1, SeqCst); + }) + .map_windows(|arr: &[i32; 2]| *arr); + assert_eq!(counter.load(SeqCst), 0); + + assert_eq!(iter.next(), Some([0, 1])); + // The first iteration consumes N items (N = 2). + assert_eq!(counter.load(SeqCst), 2); + + assert_eq!(iter.next(), Some([1, 2])); + assert_eq!(counter.load(SeqCst), 3); + + assert_eq!(iter.next(), Some([2, 3])); + assert_eq!(counter.load(SeqCst), 4); + + assert_eq!(iter.next(), Some([3, 4])); + assert_eq!(counter.load(SeqCst), 5); + + assert_eq!(iter.next(), None); + assert_eq!(counter.load(SeqCst), 5); +} + +#[test] +fn test_size_hint() { + struct SizeHintCheckHelper((usize, Option)); + + impl Iterator for SizeHintCheckHelper { + type Item = i32; + + fn next(&mut self) -> Option { + let (ref mut lo, ref mut hi) = self.0; + let next = (*hi != Some(0)).then_some(0); + *lo = lo.saturating_sub(1); + if let Some(hi) = hi { + *hi = hi.saturating_sub(1); + } + next + } + + fn size_hint(&self) -> (usize, Option) { + self.0 + } + } + + fn check_size_hint( + size_hint: (usize, Option), + mut mapped_size_hint: (usize, Option), + ) { + let mut iter = SizeHintCheckHelper(size_hint); + let mut mapped_iter = iter.by_ref().map_windows(|_: &[_; N]| ()); + while mapped_iter.size_hint().0 > 0 { + assert_eq!(mapped_iter.size_hint(), mapped_size_hint); + assert!(mapped_iter.next().is_some()); + mapped_size_hint.0 -= 1; + mapped_size_hint.1 = mapped_size_hint.1.map(|hi| hi.saturating_sub(1)); + } + } + + check_size_hint::<1>((0, None), (0, None)); + check_size_hint::<1>((0, Some(0)), (0, Some(0))); + check_size_hint::<1>((0, Some(2)), (0, Some(2))); + check_size_hint::<1>((1, None), (1, None)); + check_size_hint::<1>((1, Some(1)), (1, Some(1))); + check_size_hint::<1>((1, Some(4)), (1, Some(4))); + check_size_hint::<1>((5, None), (5, None)); + check_size_hint::<1>((5, Some(5)), (5, Some(5))); + check_size_hint::<1>((5, Some(10)), (5, Some(10))); + + check_size_hint::<2>((0, None), (0, None)); + check_size_hint::<2>((0, Some(0)), (0, Some(0))); + check_size_hint::<2>((0, Some(2)), (0, Some(1))); + check_size_hint::<2>((1, None), (0, None)); + check_size_hint::<2>((1, Some(1)), (0, Some(0))); + check_size_hint::<2>((1, Some(4)), (0, Some(3))); + check_size_hint::<2>((5, None), (4, None)); + check_size_hint::<2>((5, Some(5)), (4, Some(4))); + check_size_hint::<2>((5, Some(10)), (4, Some(9))); + + check_size_hint::<5>((0, None), (0, None)); + check_size_hint::<5>((0, Some(0)), (0, Some(0))); + check_size_hint::<5>((0, Some(2)), (0, Some(0))); + check_size_hint::<5>((1, None), (0, None)); + check_size_hint::<5>((1, Some(1)), (0, Some(0))); + check_size_hint::<5>((1, Some(4)), (0, Some(0))); + check_size_hint::<5>((5, None), (1, None)); + check_size_hint::<5>((5, Some(5)), (1, Some(1))); + check_size_hint::<5>((5, Some(10)), (1, Some(6))); +} diff --git a/library/core/tests/iter/adapters/mod.rs b/library/core/tests/iter/adapters/mod.rs index ca3463aa7f782..dedb4c0a9dd5f 100644 --- a/library/core/tests/iter/adapters/mod.rs +++ b/library/core/tests/iter/adapters/mod.rs @@ -13,6 +13,7 @@ mod fuse; mod inspect; mod intersperse; mod map; +mod map_windows; mod peekable; mod scan; mod skip; diff --git a/library/core/tests/lib.rs b/library/core/tests/lib.rs index 3933e3289514c..f14a831ae9121 100644 --- a/library/core/tests/lib.rs +++ b/library/core/tests/lib.rs @@ -109,6 +109,7 @@ #![feature(utf8_chunks)] #![feature(is_ascii_octdigit)] #![feature(get_many_mut)] +#![feature(iter_map_windows)] #![cfg_attr(not(bootstrap), feature(offset_of))] #![deny(unsafe_op_in_unsafe_fn)] #![deny(fuzzy_provenance_casts)]