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-rw-r--r--library/alloc/src/vec/mod.rs67
1 files changed, 50 insertions, 17 deletions
diff --git a/library/alloc/src/vec/mod.rs b/library/alloc/src/vec/mod.rs
index bbbdc3aa2..ba34ab680 100644
--- a/library/alloc/src/vec/mod.rs
+++ b/library/alloc/src/vec/mod.rs
@@ -1070,7 +1070,8 @@ impl<T, A: Allocator> Vec<T, A> {
/// Converts the vector into [`Box<[T]>`][owned slice].
///
- /// Note that this will drop any excess capacity.
+ /// If the vector has excess capacity, its items will be moved into a
+ /// newly-allocated buffer with exactly the right capacity.
///
/// [owned slice]: Box
///
@@ -2163,7 +2164,7 @@ impl<T, A: Allocator> Vec<T, A> {
{
let len = self.len();
if new_len > len {
- self.extend_with(new_len - len, ExtendFunc(f));
+ self.extend_trusted(iter::repeat_with(f).take(new_len - len));
} else {
self.truncate(new_len);
}
@@ -2491,16 +2492,6 @@ impl<T: Clone> ExtendWith<T> for ExtendElement<T> {
}
}
-struct ExtendFunc<F>(F);
-impl<T, F: FnMut() -> T> ExtendWith<T> for ExtendFunc<F> {
- fn next(&mut self) -> T {
- (self.0)()
- }
- fn last(mut self) -> T {
- (self.0)()
- }
-}
-
impl<T, A: Allocator> Vec<T, A> {
#[cfg(not(no_global_oom_handling))]
/// Extend the vector by `n` values, using the given generator.
@@ -2588,7 +2579,7 @@ impl<T: Clone, A: Allocator> ExtendFromWithinSpec for Vec<T, A> {
let (this, spare, len) = unsafe { self.split_at_spare_mut_with_len() };
// SAFETY:
- // - caller guaratees that src is a valid index
+ // - caller guarantees that src is a valid index
let to_clone = unsafe { this.get_unchecked(src) };
iter::zip(to_clone, spare)
@@ -2607,7 +2598,7 @@ impl<T: Copy, A: Allocator> ExtendFromWithinSpec for Vec<T, A> {
let (init, spare) = self.split_at_spare_mut();
// SAFETY:
- // - caller guaratees that `src` is a valid index
+ // - caller guarantees that `src` is a valid index
let source = unsafe { init.get_unchecked(src) };
// SAFETY:
@@ -2780,7 +2771,7 @@ impl<T, A: Allocator> IntoIterator for Vec<T, A> {
/// assert_eq!(v_iter.next(), None);
/// ```
#[inline]
- fn into_iter(self) -> IntoIter<T, A> {
+ fn into_iter(self) -> Self::IntoIter {
unsafe {
let mut me = ManuallyDrop::new(self);
let alloc = ManuallyDrop::new(ptr::read(me.allocator()));
@@ -2808,7 +2799,7 @@ impl<'a, T, A: Allocator> IntoIterator for &'a Vec<T, A> {
type Item = &'a T;
type IntoIter = slice::Iter<'a, T>;
- fn into_iter(self) -> slice::Iter<'a, T> {
+ fn into_iter(self) -> Self::IntoIter {
self.iter()
}
}
@@ -2818,7 +2809,7 @@ impl<'a, T, A: Allocator> IntoIterator for &'a mut Vec<T, A> {
type Item = &'a mut T;
type IntoIter = slice::IterMut<'a, T>;
- fn into_iter(self) -> slice::IterMut<'a, T> {
+ fn into_iter(self) -> Self::IntoIter {
self.iter_mut()
}
}
@@ -2870,6 +2861,40 @@ impl<T, A: Allocator> Vec<T, A> {
}
}
+ // specific extend for `TrustedLen` iterators, called both by the specializations
+ // and internal places where resolving specialization makes compilation slower
+ #[cfg(not(no_global_oom_handling))]
+ fn extend_trusted(&mut self, iterator: impl iter::TrustedLen<Item = T>) {
+ let (low, high) = iterator.size_hint();
+ if let Some(additional) = high {
+ debug_assert_eq!(
+ low,
+ additional,
+ "TrustedLen iterator's size hint is not exact: {:?}",
+ (low, high)
+ );
+ self.reserve(additional);
+ unsafe {
+ let ptr = self.as_mut_ptr();
+ let mut local_len = SetLenOnDrop::new(&mut self.len);
+ iterator.for_each(move |element| {
+ ptr::write(ptr.add(local_len.current_len()), element);
+ // Since the loop executes user code which can panic we have to update
+ // the length every step to correctly drop what we've written.
+ // NB can't overflow since we would have had to alloc the address space
+ local_len.increment_len(1);
+ });
+ }
+ } else {
+ // Per TrustedLen contract a `None` upper bound means that the iterator length
+ // truly exceeds usize::MAX, which would eventually lead to a capacity overflow anyway.
+ // Since the other branch already panics eagerly (via `reserve()`) we do the same here.
+ // This avoids additional codegen for a fallback code path which would eventually
+ // panic anyway.
+ panic!("capacity overflow");
+ }
+ }
+
/// Creates a splicing iterator that replaces the specified range in the vector
/// with the given `replace_with` iterator and yields the removed items.
/// `replace_with` does not need to be the same length as `range`.
@@ -3199,6 +3224,14 @@ impl<T, A: Allocator> From<Vec<T, A>> for Box<[T], A> {
/// ```
/// assert_eq!(Box::from(vec![1, 2, 3]), vec![1, 2, 3].into_boxed_slice());
/// ```
+ ///
+ /// Any excess capacity is removed:
+ /// ```
+ /// let mut vec = Vec::with_capacity(10);
+ /// vec.extend([1, 2, 3]);
+ ///
+ /// assert_eq!(Box::from(vec), vec![1, 2, 3].into_boxed_slice());
+ /// ```
fn from(v: Vec<T, A>) -> Self {
v.into_boxed_slice()
}