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Diffstat (limited to 'src/libcore/array/iter.rs')
| -rw-r--r-- | src/libcore/array/iter.rs | 236 |
1 files changed, 0 insertions, 236 deletions
diff --git a/src/libcore/array/iter.rs b/src/libcore/array/iter.rs deleted file mode 100644 index 174f7e26efb..00000000000 --- a/src/libcore/array/iter.rs +++ /dev/null @@ -1,236 +0,0 @@ -//! Defines the `IntoIter` owned iterator for arrays. - -use crate::{ - fmt, - iter::{ExactSizeIterator, FusedIterator, TrustedLen}, - mem::{self, MaybeUninit}, - ops::Range, - ptr, -}; - -/// A by-value [array] iterator. -/// -/// [array]: ../../std/primitive.array.html -#[unstable(feature = "array_value_iter", issue = "65798")] -pub struct IntoIter<T, const N: usize> { - /// This is the array we are iterating over. - /// - /// Elements with index `i` where `alive.start <= i < alive.end` have not - /// been yielded yet and are valid array entries. Elements with indices `i - /// < alive.start` or `i >= alive.end` have been yielded already and must - /// not be accessed anymore! Those dead elements might even be in a - /// completely uninitialized state! - /// - /// So the invariants are: - /// - `data[alive]` is alive (i.e. contains valid elements) - /// - `data[..alive.start]` and `data[alive.end..]` are dead (i.e. the - /// elements were already read and must not be touched anymore!) - data: [MaybeUninit<T>; N], - - /// The elements in `data` that have not been yielded yet. - /// - /// Invariants: - /// - `alive.start <= alive.end` - /// - `alive.end <= N` - alive: Range<usize>, -} - -impl<T, const N: usize> IntoIter<T, N> { - /// Creates a new iterator over the given `array`. - /// - /// *Note*: this method might never get stabilized and/or removed in the - /// future as there will likely be another, preferred way of obtaining this - /// iterator (either via `IntoIterator` for arrays or via another way). - #[unstable(feature = "array_value_iter", issue = "65798")] - pub fn new(array: [T; N]) -> Self { - // SAFETY: The transmute here is actually safe. The docs of `MaybeUninit` - // promise: - // - // > `MaybeUninit<T>` is guaranteed to have the same size and alignment - // > as `T`. - // - // The docs even show a transmute from an array of `MaybeUninit<T>` to - // an array of `T`. - // - // With that, this initialization satisfies the invariants. - - // FIXME(LukasKalbertodt): actually use `mem::transmute` here, once it - // works with const generics: - // `mem::transmute::<[T; {N}], [MaybeUninit<T>; {N}]>(array)` - // - // Until then, we do it manually here. We first create a bitwise copy - // but cast the pointer so that it is treated as a different type. Then - // we forget `array` so that it is not dropped. - let data = unsafe { - let data = ptr::read(&array as *const [T; N] as *const [MaybeUninit<T>; N]); - mem::forget(array); - data - }; - - Self { data, alive: 0..N } - } - - /// Returns an immutable slice of all elements that have not been yielded - /// yet. - fn as_slice(&self) -> &[T] { - let slice = &self.data[self.alive.clone()]; - // SAFETY: This transmute is safe. As mentioned in `new`, `MaybeUninit` retains - // the size and alignment of `T`. Furthermore, we know that all - // elements within `alive` are properly initialized. - unsafe { mem::transmute::<&[MaybeUninit<T>], &[T]>(slice) } - } - - /// Returns a mutable slice of all elements that have not been yielded yet. - fn as_mut_slice(&mut self) -> &mut [T] { - // This transmute is safe, same as in `as_slice` above. - let slice = &mut self.data[self.alive.clone()]; - // SAFETY: This transmute is safe. As mentioned in `new`, `MaybeUninit` retains - // the size and alignment of `T`. Furthermore, we know that all - // elements within `alive` are properly initialized. - unsafe { mem::transmute::<&mut [MaybeUninit<T>], &mut [T]>(slice) } - } -} - -#[stable(feature = "array_value_iter_impls", since = "1.40.0")] -impl<T, const N: usize> Iterator for IntoIter<T, N> { - type Item = T; - fn next(&mut self) -> Option<Self::Item> { - if self.alive.start == self.alive.end { - return None; - } - - // Bump start index. - // - // From the check above we know that `alive.start != alive.end`. - // Combine this with the invariant `alive.start <= alive.end`, we know - // that `alive.start < alive.end`. Increasing `alive.start` by 1 - // maintains the invariant regarding `alive`. However, due to this - // change, for a short time, the alive zone is not `data[alive]` - // anymore, but `data[idx..alive.end]`. - let idx = self.alive.start; - self.alive.start += 1; - - // Read the element from the array. - // SAFETY: This is safe: `idx` is an index - // into the "alive" region of the array. Reading this element means - // that `data[idx]` is regarded as dead now (i.e. do not touch). As - // `idx` was the start of the alive-zone, the alive zone is now - // `data[alive]` again, restoring all invariants. - let out = unsafe { self.data.get_unchecked(idx).read() }; - - Some(out) - } - - fn size_hint(&self) -> (usize, Option<usize>) { - let len = self.len(); - (len, Some(len)) - } - - fn count(self) -> usize { - self.len() - } - - fn last(mut self) -> Option<Self::Item> { - self.next_back() - } -} - -#[stable(feature = "array_value_iter_impls", since = "1.40.0")] -impl<T, const N: usize> DoubleEndedIterator for IntoIter<T, N> { - fn next_back(&mut self) -> Option<Self::Item> { - if self.alive.start == self.alive.end { - return None; - } - - // Decrease end index. - // - // From the check above we know that `alive.start != alive.end`. - // Combine this with the invariant `alive.start <= alive.end`, we know - // that `alive.start < alive.end`. As `alive.start` cannot be negative, - // `alive.end` is at least 1, meaning that we can safely decrement it - // by one. This also maintains the invariant `alive.start <= - // alive.end`. However, due to this change, for a short time, the alive - // zone is not `data[alive]` anymore, but `data[alive.start..alive.end - // + 1]`. - self.alive.end -= 1; - - // Read the element from the array. - // SAFETY: This is safe: `alive.end` is an - // index into the "alive" region of the array. Compare the previous - // comment that states that the alive region is - // `data[alive.start..alive.end + 1]`. Reading this element means that - // `data[alive.end]` is regarded as dead now (i.e. do not touch). As - // `alive.end` was the end of the alive-zone, the alive zone is now - // `data[alive]` again, restoring all invariants. - let out = unsafe { self.data.get_unchecked(self.alive.end).read() }; - - Some(out) - } -} - -#[stable(feature = "array_value_iter_impls", since = "1.40.0")] -impl<T, const N: usize> Drop for IntoIter<T, N> { - fn drop(&mut self) { - // SAFETY: This is safe: `as_mut_slice` returns exactly the sub-slice - // of elements that have not been moved out yet and that remain - // to be dropped. - unsafe { ptr::drop_in_place(self.as_mut_slice()) } - } -} - -#[stable(feature = "array_value_iter_impls", since = "1.40.0")] -impl<T, const N: usize> ExactSizeIterator for IntoIter<T, N> { - fn len(&self) -> usize { - // Will never underflow due to the invariant `alive.start <= - // alive.end`. - self.alive.end - self.alive.start - } - fn is_empty(&self) -> bool { - self.alive.is_empty() - } -} - -#[stable(feature = "array_value_iter_impls", since = "1.40.0")] -impl<T, const N: usize> FusedIterator for IntoIter<T, N> {} - -// The iterator indeed reports the correct length. The number of "alive" -// elements (that will still be yielded) is the length of the range `alive`. -// This range is decremented in length in either `next` or `next_back`. It is -// always decremented by 1 in those methods, but only if `Some(_)` is returned. -#[stable(feature = "array_value_iter_impls", since = "1.40.0")] -unsafe impl<T, const N: usize> TrustedLen for IntoIter<T, N> {} - -#[stable(feature = "array_value_iter_impls", since = "1.40.0")] -impl<T: Clone, const N: usize> Clone for IntoIter<T, N> { - fn clone(&self) -> Self { - // SAFETY: each point of unsafety is documented inside the unsafe block - unsafe { - // This creates a new uninitialized array. Note that the `assume_init` - // refers to the array, not the individual elements. And it is Ok if - // the array is in an uninitialized state as all elements may be - // uninitialized (all bit patterns are valid). Compare the - // `MaybeUninit` docs for more information. - let mut new_data: [MaybeUninit<T>; N] = MaybeUninit::uninit().assume_init(); - - // Clone all alive elements. - for idx in self.alive.clone() { - // The element at `idx` in the old array is alive, so we can - // safely call `get_ref()`. We then clone it, and write the - // clone into the new array. - let clone = self.data.get_unchecked(idx).get_ref().clone(); - new_data.get_unchecked_mut(idx).write(clone); - } - - Self { data: new_data, alive: self.alive.clone() } - } - } -} - -#[stable(feature = "array_value_iter_impls", since = "1.40.0")] -impl<T: fmt::Debug, const N: usize> fmt::Debug for IntoIter<T, N> { - fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { - // Only print the elements that were not yielded yet: we cannot - // access the yielded elements anymore. - f.debug_tuple("IntoIter").field(&self.as_slice()).finish() - } -} |