1// SPDX-License-Identifier: Apache-2.0 OR MIT
2
3#[cfg(not(no_global_oom_handling))]
4use super::AsVecIntoIter;
5use crate::alloc::{Allocator, Global};
6#[cfg(not(no_global_oom_handling))]
7use crate::collections::VecDeque;
8use crate::raw_vec::RawVec;
9use core::array;
10use core::fmt;
11use core::iter::{
12    FusedIterator, InPlaceIterable, SourceIter, TrustedLen, TrustedRandomAccessNoCoerce,
13};
14use core::marker::PhantomData;
15use core::mem::{self, ManuallyDrop, MaybeUninit, SizedTypeProperties};
16use core::num::NonZeroUsize;
17#[cfg(not(no_global_oom_handling))]
18use core::ops::Deref;
19use core::ptr::{self, NonNull};
20use core::slice::{self};
21
22/// An iterator that moves out of a vector.
23///
24/// This `struct` is created by the `into_iter` method on [`Vec`](super::Vec)
25/// (provided by the [`IntoIterator`] trait).
26///
27/// # Example
28///
29/// ```
30/// let v = vec![0, 1, 2];
31/// let iter: std::vec::IntoIter<_> = v.into_iter();
32/// ```
33#[stable(feature = "rust1", since = "1.0.0")]
34#[rustc_insignificant_dtor]
35pub struct IntoIter<
36    T,
37    #[unstable(feature = "allocator_api", issue = "32838")] A: Allocator = Global,
38> {
39    pub(super) buf: NonNull<T>,
40    pub(super) phantom: PhantomData<T>,
41    pub(super) cap: usize,
42    // the drop impl reconstructs a RawVec from buf, cap and alloc
43    // to avoid dropping the allocator twice we need to wrap it into ManuallyDrop
44    pub(super) alloc: ManuallyDrop<A>,
45    pub(super) ptr: *const T,
46    pub(super) end: *const T, // If T is a ZST, this is actually ptr+len. This encoding is picked so that
47                              // ptr == end is a quick test for the Iterator being empty, that works
48                              // for both ZST and non-ZST.
49}
50
51#[stable(feature = "vec_intoiter_debug", since = "1.13.0")]
52impl<T: fmt::Debug, A: Allocator> fmt::Debug for IntoIter<T, A> {
53    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
54        f.debug_tuple("IntoIter").field(&self.as_slice()).finish()
55    }
56}
57
58impl<T, A: Allocator> IntoIter<T, A> {
59    /// Returns the remaining items of this iterator as a slice.
60    ///
61    /// # Examples
62    ///
63    /// ```
64    /// let vec = vec!['a', 'b', 'c'];
65    /// let mut into_iter = vec.into_iter();
66    /// assert_eq!(into_iter.as_slice(), &['a', 'b', 'c']);
67    /// let _ = into_iter.next().unwrap();
68    /// assert_eq!(into_iter.as_slice(), &['b', 'c']);
69    /// ```
70    #[stable(feature = "vec_into_iter_as_slice", since = "1.15.0")]
71    pub fn as_slice(&self) -> &[T] {
72        unsafe { slice::from_raw_parts(self.ptr, self.len()) }
73    }
74
75    /// Returns the remaining items of this iterator as a mutable slice.
76    ///
77    /// # Examples
78    ///
79    /// ```
80    /// let vec = vec!['a', 'b', 'c'];
81    /// let mut into_iter = vec.into_iter();
82    /// assert_eq!(into_iter.as_slice(), &['a', 'b', 'c']);
83    /// into_iter.as_mut_slice()[2] = 'z';
84    /// assert_eq!(into_iter.next().unwrap(), 'a');
85    /// assert_eq!(into_iter.next().unwrap(), 'b');
86    /// assert_eq!(into_iter.next().unwrap(), 'z');
87    /// ```
88    #[stable(feature = "vec_into_iter_as_slice", since = "1.15.0")]
89    pub fn as_mut_slice(&mut self) -> &mut [T] {
90        unsafe { &mut *self.as_raw_mut_slice() }
91    }
92
93    /// Returns a reference to the underlying allocator.
94    #[unstable(feature = "allocator_api", issue = "32838")]
95    #[inline]
96    pub fn allocator(&self) -> &A {
97        &self.alloc
98    }
99
100    fn as_raw_mut_slice(&mut self) -> *mut [T] {
101        ptr::slice_from_raw_parts_mut(self.ptr as *mut T, self.len())
102    }
103
104    /// Drops remaining elements and relinquishes the backing allocation.
105    /// This method guarantees it won't panic before relinquishing
106    /// the backing allocation.
107    ///
108    /// This is roughly equivalent to the following, but more efficient
109    ///
110    /// ```
111    /// # let mut into_iter = Vec::<u8>::with_capacity(10).into_iter();
112    /// let mut into_iter = std::mem::replace(&mut into_iter, Vec::new().into_iter());
113    /// (&mut into_iter).for_each(drop);
114    /// std::mem::forget(into_iter);
115    /// ```
116    ///
117    /// This method is used by in-place iteration, refer to the vec::in_place_collect
118    /// documentation for an overview.
119    #[cfg(not(no_global_oom_handling))]
120    pub(super) fn forget_allocation_drop_remaining(&mut self) {
121        let remaining = self.as_raw_mut_slice();
122
123        // overwrite the individual fields instead of creating a new
124        // struct and then overwriting &mut self.
125        // this creates less assembly
126        self.cap = 0;
127        self.buf = unsafe { NonNull::new_unchecked(RawVec::NEW.ptr()) };
128        self.ptr = self.buf.as_ptr();
129        self.end = self.buf.as_ptr();
130
131        // Dropping the remaining elements can panic, so this needs to be
132        // done only after updating the other fields.
133        unsafe {
134            ptr::drop_in_place(remaining);
135        }
136    }
137
138    /// Forgets to Drop the remaining elements while still allowing the backing allocation to be freed.
139    pub(crate) fn forget_remaining_elements(&mut self) {
140        // For th ZST case, it is crucial that we mutate `end` here, not `ptr`.
141        // `ptr` must stay aligned, while `end` may be unaligned.
142        self.end = self.ptr;
143    }
144
145    #[cfg(not(no_global_oom_handling))]
146    #[inline]
147    pub(crate) fn into_vecdeque(self) -> VecDeque<T, A> {
148        // Keep our `Drop` impl from dropping the elements and the allocator
149        let mut this = ManuallyDrop::new(self);
150
151        // SAFETY: This allocation originally came from a `Vec`, so it passes
152        // all those checks. We have `this.buf` ≤ `this.ptr` ≤ `this.end`,
153        // so the `sub_ptr`s below cannot wrap, and will produce a well-formed
154        // range. `end` ≤ `buf + cap`, so the range will be in-bounds.
155        // Taking `alloc` is ok because nothing else is going to look at it,
156        // since our `Drop` impl isn't going to run so there's no more code.
157        unsafe {
158            let buf = this.buf.as_ptr();
159            let initialized = if T::IS_ZST {
160                // All the pointers are the same for ZSTs, so it's fine to
161                // say that they're all at the beginning of the "allocation".
162                0..this.len()
163            } else {
164                this.ptr.sub_ptr(buf)..this.end.sub_ptr(buf)
165            };
166            let cap = this.cap;
167            let alloc = ManuallyDrop::take(&mut this.alloc);
168            VecDeque::from_contiguous_raw_parts_in(buf, initialized, cap, alloc)
169        }
170    }
171}
172
173#[stable(feature = "vec_intoiter_as_ref", since = "1.46.0")]
174impl<T, A: Allocator> AsRef<[T]> for IntoIter<T, A> {
175    fn as_ref(&self) -> &[T] {
176        self.as_slice()
177    }
178}
179
180#[stable(feature = "rust1", since = "1.0.0")]
181unsafe impl<T: Send, A: Allocator + Send> Send for IntoIter<T, A> {}
182#[stable(feature = "rust1", since = "1.0.0")]
183unsafe impl<T: Sync, A: Allocator + Sync> Sync for IntoIter<T, A> {}
184
185#[stable(feature = "rust1", since = "1.0.0")]
186impl<T, A: Allocator> Iterator for IntoIter<T, A> {
187    type Item = T;
188
189    #[inline]
190    fn next(&mut self) -> Option<T> {
191        if self.ptr == self.end {
192            None
193        } else if T::IS_ZST {
194            // `ptr` has to stay where it is to remain aligned, so we reduce the length by 1 by
195            // reducing the `end`.
196            self.end = self.end.wrapping_byte_sub(1);
197
198            // Make up a value of this ZST.
199            Some(unsafe { mem::zeroed() })
200        } else {
201            let old = self.ptr;
202            self.ptr = unsafe { self.ptr.add(1) };
203
204            Some(unsafe { ptr::read(old) })
205        }
206    }
207
208    #[inline]
209    fn size_hint(&self) -> (usize, Option<usize>) {
210        let exact = if T::IS_ZST {
211            self.end.addr().wrapping_sub(self.ptr.addr())
212        } else {
213            unsafe { self.end.sub_ptr(self.ptr) }
214        };
215        (exact, Some(exact))
216    }
217
218    #[inline]
219    fn advance_by(&mut self, n: usize) -> Result<(), NonZeroUsize> {
220        let step_size = self.len().min(n);
221        let to_drop = ptr::slice_from_raw_parts_mut(self.ptr as *mut T, step_size);
222        if T::IS_ZST {
223            // See `next` for why we sub `end` here.
224            self.end = self.end.wrapping_byte_sub(step_size);
225        } else {
226            // SAFETY: the min() above ensures that step_size is in bounds
227            self.ptr = unsafe { self.ptr.add(step_size) };
228        }
229        // SAFETY: the min() above ensures that step_size is in bounds
230        unsafe {
231            ptr::drop_in_place(to_drop);
232        }
233        NonZeroUsize::new(n - step_size).map_or(Ok(()), Err)
234    }
235
236    #[inline]
237    fn count(self) -> usize {
238        self.len()
239    }
240
241    #[inline]
242    fn next_chunk<const N: usize>(&mut self) -> Result<[T; N], core::array::IntoIter<T, N>> {
243        let mut raw_ary = MaybeUninit::uninit_array();
244
245        let len = self.len();
246
247        if T::IS_ZST {
248            if len < N {
249                self.forget_remaining_elements();
250                // Safety: ZSTs can be conjured ex nihilo, only the amount has to be correct
251                return Err(unsafe { array::IntoIter::new_unchecked(raw_ary, 0..len) });
252            }
253
254            self.end = self.end.wrapping_byte_sub(N);
255            // Safety: ditto
256            return Ok(unsafe { raw_ary.transpose().assume_init() });
257        }
258
259        if len < N {
260            // Safety: `len` indicates that this many elements are available and we just checked that
261            // it fits into the array.
262            unsafe {
263                ptr::copy_nonoverlapping(self.ptr, raw_ary.as_mut_ptr() as *mut T, len);
264                self.forget_remaining_elements();
265                return Err(array::IntoIter::new_unchecked(raw_ary, 0..len));
266            }
267        }
268
269        // Safety: `len` is larger than the array size. Copy a fixed amount here to fully initialize
270        // the array.
271        return unsafe {
272            ptr::copy_nonoverlapping(self.ptr, raw_ary.as_mut_ptr() as *mut T, N);
273            self.ptr = self.ptr.add(N);
274            Ok(raw_ary.transpose().assume_init())
275        };
276    }
277
278    unsafe fn __iterator_get_unchecked(&mut self, i: usize) -> Self::Item
279    where
280        Self: TrustedRandomAccessNoCoerce,
281    {
282        // SAFETY: the caller must guarantee that `i` is in bounds of the
283        // `Vec<T>`, so `i` cannot overflow an `isize`, and the `self.ptr.add(i)`
284        // is guaranteed to pointer to an element of the `Vec<T>` and
285        // thus guaranteed to be valid to dereference.
286        //
287        // Also note the implementation of `Self: TrustedRandomAccess` requires
288        // that `T: Copy` so reading elements from the buffer doesn't invalidate
289        // them for `Drop`.
290        unsafe {
291            if T::IS_ZST { mem::zeroed() } else { ptr::read(self.ptr.add(i)) }
292        }
293    }
294}
295
296#[stable(feature = "rust1", since = "1.0.0")]
297impl<T, A: Allocator> DoubleEndedIterator for IntoIter<T, A> {
298    #[inline]
299    fn next_back(&mut self) -> Option<T> {
300        if self.end == self.ptr {
301            None
302        } else if T::IS_ZST {
303            // See above for why 'ptr.offset' isn't used
304            self.end = self.end.wrapping_byte_sub(1);
305
306            // Make up a value of this ZST.
307            Some(unsafe { mem::zeroed() })
308        } else {
309            self.end = unsafe { self.end.sub(1) };
310
311            Some(unsafe { ptr::read(self.end) })
312        }
313    }
314
315    #[inline]
316    fn advance_back_by(&mut self, n: usize) -> Result<(), NonZeroUsize> {
317        let step_size = self.len().min(n);
318        if T::IS_ZST {
319            // SAFETY: same as for advance_by()
320            self.end = self.end.wrapping_byte_sub(step_size);
321        } else {
322            // SAFETY: same as for advance_by()
323            self.end = unsafe { self.end.sub(step_size) };
324        }
325        let to_drop = ptr::slice_from_raw_parts_mut(self.end as *mut T, step_size);
326        // SAFETY: same as for advance_by()
327        unsafe {
328            ptr::drop_in_place(to_drop);
329        }
330        NonZeroUsize::new(n - step_size).map_or(Ok(()), Err)
331    }
332}
333
334#[stable(feature = "rust1", since = "1.0.0")]
335impl<T, A: Allocator> ExactSizeIterator for IntoIter<T, A> {
336    fn is_empty(&self) -> bool {
337        self.ptr == self.end
338    }
339}
340
341#[stable(feature = "fused", since = "1.26.0")]
342impl<T, A: Allocator> FusedIterator for IntoIter<T, A> {}
343
344#[unstable(feature = "trusted_len", issue = "37572")]
345unsafe impl<T, A: Allocator> TrustedLen for IntoIter<T, A> {}
346
347#[stable(feature = "default_iters", since = "1.70.0")]
348impl<T, A> Default for IntoIter<T, A>
349where
350    A: Allocator + Default,
351{
352    /// Creates an empty `vec::IntoIter`.
353    ///
354    /// ```
355    /// # use std::vec;
356    /// let iter: vec::IntoIter<u8> = Default::default();
357    /// assert_eq!(iter.len(), 0);
358    /// assert_eq!(iter.as_slice(), &[]);
359    /// ```
360    fn default() -> Self {
361        super::Vec::new_in(Default::default()).into_iter()
362    }
363}
364
365#[doc(hidden)]
366#[unstable(issue = "none", feature = "std_internals")]
367#[rustc_unsafe_specialization_marker]
368pub trait NonDrop {}
369
370// T: Copy as approximation for !Drop since get_unchecked does not advance self.ptr
371// and thus we can't implement drop-handling
372#[unstable(issue = "none", feature = "std_internals")]
373impl<T: Copy> NonDrop for T {}
374
375#[doc(hidden)]
376#[unstable(issue = "none", feature = "std_internals")]
377// TrustedRandomAccess (without NoCoerce) must not be implemented because
378// subtypes/supertypes of `T` might not be `NonDrop`
379unsafe impl<T, A: Allocator> TrustedRandomAccessNoCoerce for IntoIter<T, A>
380where
381    T: NonDrop,
382{
383    const MAY_HAVE_SIDE_EFFECT: bool = false;
384}
385
386#[cfg(not(no_global_oom_handling))]
387#[stable(feature = "vec_into_iter_clone", since = "1.8.0")]
388impl<T: Clone, A: Allocator + Clone> Clone for IntoIter<T, A> {
389    #[cfg(not(test))]
390    fn clone(&self) -> Self {
391        self.as_slice().to_vec_in(self.alloc.deref().clone()).into_iter()
392    }
393    #[cfg(test)]
394    fn clone(&self) -> Self {
395        crate::slice::to_vec(self.as_slice(), self.alloc.deref().clone()).into_iter()
396    }
397}
398
399#[stable(feature = "rust1", since = "1.0.0")]
400unsafe impl<#[may_dangle] T, A: Allocator> Drop for IntoIter<T, A> {
401    fn drop(&mut self) {
402        struct DropGuard<'a, T, A: Allocator>(&'a mut IntoIter<T, A>);
403
404        impl<T, A: Allocator> Drop for DropGuard<'_, T, A> {
405            fn drop(&mut self) {
406                unsafe {
407                    // `IntoIter::alloc` is not used anymore after this and will be dropped by RawVec
408                    let alloc = ManuallyDrop::take(&mut self.0.alloc);
409                    // RawVec handles deallocation
410                    let _ = RawVec::from_raw_parts_in(self.0.buf.as_ptr(), self.0.cap, alloc);
411                }
412            }
413        }
414
415        let guard = DropGuard(self);
416        // destroy the remaining elements
417        unsafe {
418            ptr::drop_in_place(guard.0.as_raw_mut_slice());
419        }
420        // now `guard` will be dropped and do the rest
421    }
422}
423
424// In addition to the SAFETY invariants of the following three unsafe traits
425// also refer to the vec::in_place_collect module documentation to get an overview
426#[unstable(issue = "none", feature = "inplace_iteration")]
427#[doc(hidden)]
428unsafe impl<T, A: Allocator> InPlaceIterable for IntoIter<T, A> {}
429
430#[unstable(issue = "none", feature = "inplace_iteration")]
431#[doc(hidden)]
432unsafe impl<T, A: Allocator> SourceIter for IntoIter<T, A> {
433    type Source = Self;
434
435    #[inline]
436    unsafe fn as_inner(&mut self) -> &mut Self::Source {
437        self
438    }
439}
440
441#[cfg(not(no_global_oom_handling))]
442unsafe impl<T> AsVecIntoIter for IntoIter<T> {
443    type Item = T;
444
445    fn as_into_iter(&mut self) -> &mut IntoIter<Self::Item> {
446        self
447    }
448}
449