1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
#[cfg(not(no_global_oom_handling))]
use super::AsVecIntoIter;
use crate::alloc::{Allocator, Global};
use crate::raw_vec::RawVec;
use core::fmt;
use core::intrinsics::arith_offset;
use core::iter::{
    FusedIterator, InPlaceIterable, SourceIter, TrustedLen, TrustedRandomAccessNoCoerce,
};
use core::marker::PhantomData;
use core::mem::{self, ManuallyDrop};
#[cfg(not(no_global_oom_handling))]
use core::ops::Deref;
use core::ptr::{self, NonNull};
use core::slice::{self};

/// An iterator that moves out of a vector.
///
/// This `struct` is created by the `into_iter` method on [`Vec`](super::Vec)
/// (provided by the [`IntoIterator`] trait).
///
/// # Example
///
/// ```
/// let v = vec![0, 1, 2];
/// let iter: std::vec::IntoIter<_> = v.into_iter();
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_insignificant_dtor]
pub struct IntoIter<
    T,
    #[unstable(feature = "allocator_api", issue = "32838")] A: Allocator = Global,
> {
    pub(super) buf: NonNull<T>,
    pub(super) phantom: PhantomData<T>,
    pub(super) cap: usize,
    // the drop impl reconstructs a RawVec from buf, cap and alloc
    // to avoid dropping the allocator twice we need to wrap it into ManuallyDrop
    pub(super) alloc: ManuallyDrop<A>,
    pub(super) ptr: *const T,
    pub(super) end: *const T,
}

#[stable(feature = "vec_intoiter_debug", since = "1.13.0")]
impl<T: fmt::Debug, A: Allocator> fmt::Debug for IntoIter<T, A> {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_tuple("IntoIter").field(&self.as_slice()).finish()
    }
}

impl<T, A: Allocator> IntoIter<T, A> {
    /// Returns the remaining items of this iterator as a slice.
    ///
    /// # Examples
    ///
    /// ```
    /// let vec = vec!['a', 'b', 'c'];
    /// let mut into_iter = vec.into_iter();
    /// assert_eq!(into_iter.as_slice(), &['a', 'b', 'c']);
    /// let _ = into_iter.next().unwrap();
    /// assert_eq!(into_iter.as_slice(), &['b', 'c']);
    /// ```
    #[stable(feature = "vec_into_iter_as_slice", since = "1.15.0")]
    pub fn as_slice(&self) -> &[T] {
        unsafe { slice::from_raw_parts(self.ptr, self.len()) }
    }

    /// Returns the remaining items of this iterator as a mutable slice.
    ///
    /// # Examples
    ///
    /// ```
    /// let vec = vec!['a', 'b', 'c'];
    /// let mut into_iter = vec.into_iter();
    /// assert_eq!(into_iter.as_slice(), &['a', 'b', 'c']);
    /// into_iter.as_mut_slice()[2] = 'z';
    /// assert_eq!(into_iter.next().unwrap(), 'a');
    /// assert_eq!(into_iter.next().unwrap(), 'b');
    /// assert_eq!(into_iter.next().unwrap(), 'z');
    /// ```
    #[stable(feature = "vec_into_iter_as_slice", since = "1.15.0")]
    pub fn as_mut_slice(&mut self) -> &mut [T] {
        unsafe { &mut *self.as_raw_mut_slice() }
    }

    /// Returns a reference to the underlying allocator.
    #[unstable(feature = "allocator_api", issue = "32838")]
    #[inline]
    pub fn allocator(&self) -> &A {
        &self.alloc
    }

    fn as_raw_mut_slice(&mut self) -> *mut [T] {
        ptr::slice_from_raw_parts_mut(self.ptr as *mut T, self.len())
    }

    /// Drops remaining elements and relinquishes the backing allocation.
    ///
    /// This is roughly equivalent to the following, but more efficient
    ///
    /// ```
    /// # let mut into_iter = Vec::<u8>::with_capacity(10).into_iter();
    /// (&mut into_iter).for_each(core::mem::drop);
    /// unsafe { core::ptr::write(&mut into_iter, Vec::new().into_iter()); }
    /// ```
    ///
    /// This method is used by in-place iteration, refer to the vec::in_place_collect
    /// documentation for an overview.
    #[cfg(not(no_global_oom_handling))]
    pub(super) fn forget_allocation_drop_remaining(&mut self) {
        let remaining = self.as_raw_mut_slice();

        // overwrite the individual fields instead of creating a new
        // struct and then overwriting &mut self.
        // this creates less assembly
        self.cap = 0;
        self.buf = unsafe { NonNull::new_unchecked(RawVec::NEW.ptr()) };
        self.ptr = self.buf.as_ptr();
        self.end = self.buf.as_ptr();

        unsafe {
            ptr::drop_in_place(remaining);
        }
    }

    /// Forgets to Drop the remaining elements while still allowing the backing allocation to be freed.
    #[cfg(not(no_global_oom_handling))]
    pub(crate) fn forget_remaining_elements(&mut self) {
        self.ptr = self.end;
    }
}

#[stable(feature = "vec_intoiter_as_ref", since = "1.46.0")]
impl<T, A: Allocator> AsRef<[T]> for IntoIter<T, A> {
    fn as_ref(&self) -> &[T] {
        self.as_slice()
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
unsafe impl<T: Send, A: Allocator + Send> Send for IntoIter<T, A> {}
#[stable(feature = "rust1", since = "1.0.0")]
unsafe impl<T: Sync, A: Allocator + Sync> Sync for IntoIter<T, A> {}

#[stable(feature = "rust1", since = "1.0.0")]
impl<T, A: Allocator> Iterator for IntoIter<T, A> {
    type Item = T;

    #[inline]
    fn next(&mut self) -> Option<T> {
        if self.ptr as *const _ == self.end {
            None
        } else if mem::size_of::<T>() == 0 {
            // purposefully don't use 'ptr.offset' because for
            // vectors with 0-size elements this would return the
            // same pointer.
            self.ptr = unsafe { arith_offset(self.ptr as *const i8, 1) as *mut T };

            // Make up a value of this ZST.
            Some(unsafe { mem::zeroed() })
        } else {
            let old = self.ptr;
            self.ptr = unsafe { self.ptr.offset(1) };

            Some(unsafe { ptr::read(old) })
        }
    }

    #[inline]
    fn size_hint(&self) -> (usize, Option<usize>) {
        let exact = if mem::size_of::<T>() == 0 {
            self.end.addr().wrapping_sub(self.ptr.addr())
        } else {
            unsafe { self.end.sub_ptr(self.ptr) }
        };
        (exact, Some(exact))
    }

    #[inline]
    fn advance_by(&mut self, n: usize) -> Result<(), usize> {
        let step_size = self.len().min(n);
        let to_drop = ptr::slice_from_raw_parts_mut(self.ptr as *mut T, step_size);
        if mem::size_of::<T>() == 0 {
            // SAFETY: due to unchecked casts of unsigned amounts to signed offsets the wraparound
            // effectively results in unsigned pointers representing positions 0..usize::MAX,
            // which is valid for ZSTs.
            self.ptr = unsafe { arith_offset(self.ptr as *const i8, step_size as isize) as *mut T }
        } else {
            // SAFETY: the min() above ensures that step_size is in bounds
            self.ptr = unsafe { self.ptr.add(step_size) };
        }
        // SAFETY: the min() above ensures that step_size is in bounds
        unsafe {
            ptr::drop_in_place(to_drop);
        }
        if step_size < n {
            return Err(step_size);
        }
        Ok(())
    }

    #[inline]
    fn count(self) -> usize {
        self.len()
    }

    unsafe fn __iterator_get_unchecked(&mut self, i: usize) -> Self::Item
    where
        Self: TrustedRandomAccessNoCoerce,
    {
        // SAFETY: the caller must guarantee that `i` is in bounds of the
        // `Vec<T>`, so `i` cannot overflow an `isize`, and the `self.ptr.add(i)`
        // is guaranteed to pointer to an element of the `Vec<T>` and
        // thus guaranteed to be valid to dereference.
        //
        // Also note the implementation of `Self: TrustedRandomAccess` requires
        // that `T: Copy` so reading elements from the buffer doesn't invalidate
        // them for `Drop`.
        unsafe {
            if mem::size_of::<T>() == 0 { mem::zeroed() } else { ptr::read(self.ptr.add(i)) }
        }
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
impl<T, A: Allocator> DoubleEndedIterator for IntoIter<T, A> {
    #[inline]
    fn next_back(&mut self) -> Option<T> {
        if self.end == self.ptr {
            None
        } else if mem::size_of::<T>() == 0 {
            // See above for why 'ptr.offset' isn't used
            self.end = unsafe { arith_offset(self.end as *const i8, -1) as *mut T };

            // Make up a value of this ZST.
            Some(unsafe { mem::zeroed() })
        } else {
            self.end = unsafe { self.end.offset(-1) };

            Some(unsafe { ptr::read(self.end) })
        }
    }

    #[inline]
    fn advance_back_by(&mut self, n: usize) -> Result<(), usize> {
        let step_size = self.len().min(n);
        if mem::size_of::<T>() == 0 {
            // SAFETY: same as for advance_by()
            self.end = unsafe {
                arith_offset(self.end as *const i8, step_size.wrapping_neg() as isize) as *mut T
            }
        } else {
            // SAFETY: same as for advance_by()
            self.end = unsafe { self.end.offset(step_size.wrapping_neg() as isize) };
        }
        let to_drop = ptr::slice_from_raw_parts_mut(self.end as *mut T, step_size);
        // SAFETY: same as for advance_by()
        unsafe {
            ptr::drop_in_place(to_drop);
        }
        if step_size < n {
            return Err(step_size);
        }
        Ok(())
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
impl<T, A: Allocator> ExactSizeIterator for IntoIter<T, A> {
    fn is_empty(&self) -> bool {
        self.ptr == self.end
    }
}

#[stable(feature = "fused", since = "1.26.0")]
impl<T, A: Allocator> FusedIterator for IntoIter<T, A> {}

#[unstable(feature = "trusted_len", issue = "37572")]
unsafe impl<T, A: Allocator> TrustedLen for IntoIter<T, A> {}

#[doc(hidden)]
#[unstable(issue = "none", feature = "std_internals")]
#[rustc_unsafe_specialization_marker]
pub trait NonDrop {}

// T: Copy as approximation for !Drop since get_unchecked does not advance self.ptr
// and thus we can't implement drop-handling
#[unstable(issue = "none", feature = "std_internals")]
impl<T: Copy> NonDrop for T {}

#[doc(hidden)]
#[unstable(issue = "none", feature = "std_internals")]
// TrustedRandomAccess (without NoCoerce) must not be implemented because
// subtypes/supertypes of `T` might not be `NonDrop`
unsafe impl<T, A: Allocator> TrustedRandomAccessNoCoerce for IntoIter<T, A>
where
    T: NonDrop,
{
    const MAY_HAVE_SIDE_EFFECT: bool = false;
}

#[cfg(not(no_global_oom_handling))]
#[stable(feature = "vec_into_iter_clone", since = "1.8.0")]
impl<T: Clone, A: Allocator + Clone> Clone for IntoIter<T, A> {
    #[cfg(not(test))]
    fn clone(&self) -> Self {
        self.as_slice().to_vec_in(self.alloc.deref().clone()).into_iter()
    }
    #[cfg(test)]
    fn clone(&self) -> Self {
        crate::slice::to_vec(self.as_slice(), self.alloc.deref().clone()).into_iter()
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
unsafe impl<#[may_dangle] T, A: Allocator> Drop for IntoIter<T, A> {
    fn drop(&mut self) {
        struct DropGuard<'a, T, A: Allocator>(&'a mut IntoIter<T, A>);

        impl<T, A: Allocator> Drop for DropGuard<'_, T, A> {
            fn drop(&mut self) {
                unsafe {
                    // `IntoIter::alloc` is not used anymore after this and will be dropped by RawVec
                    let alloc = ManuallyDrop::take(&mut self.0.alloc);
                    // RawVec handles deallocation
                    let _ = RawVec::from_raw_parts_in(self.0.buf.as_ptr(), self.0.cap, alloc);
                }
            }
        }

        let guard = DropGuard(self);
        // destroy the remaining elements
        unsafe {
            ptr::drop_in_place(guard.0.as_raw_mut_slice());
        }
        // now `guard` will be dropped and do the rest
    }
}

// In addition to the SAFETY invariants of the following three unsafe traits
// also refer to the vec::in_place_collect module documentation to get an overview
#[unstable(issue = "none", feature = "inplace_iteration")]
#[doc(hidden)]
unsafe impl<T, A: Allocator> InPlaceIterable for IntoIter<T, A> {}

#[unstable(issue = "none", feature = "inplace_iteration")]
#[doc(hidden)]
unsafe impl<T, A: Allocator> SourceIter for IntoIter<T, A> {
    type Source = Self;

    #[inline]
    unsafe fn as_inner(&mut self) -> &mut Self::Source {
        self
    }
}

#[cfg(not(no_global_oom_handling))]
unsafe impl<T> AsVecIntoIter for IntoIter<T> {
    type Item = T;

    fn as_into_iter(&mut self) -> &mut IntoIter<Self::Item> {
        self
    }
}