1 use crate::alloc
::Allocator
;
2 use core
::iter
::TrustedLen
;
4 use core
::slice
::{self}
;
6 use super::{IntoIter, SetLenOnDrop, Vec}
;
8 // Specialization trait used for Vec::extend
9 pub(super) trait SpecExtend
<T
, I
> {
10 fn spec_extend(&mut self, iter
: I
);
13 impl<T
, I
, A
: Allocator
> SpecExtend
<T
, I
> for Vec
<T
, A
>
15 I
: Iterator
<Item
= T
>,
17 default fn spec_extend(&mut self, iter
: I
) {
18 self.extend_desugared(iter
)
22 impl<T
, I
, A
: Allocator
> SpecExtend
<T
, I
> for Vec
<T
, A
>
24 I
: TrustedLen
<Item
= T
>,
26 default fn spec_extend(&mut self, iterator
: I
) {
27 // This is the case for a TrustedLen iterator.
28 let (low
, high
) = iterator
.size_hint();
29 if let Some(additional
) = high
{
33 "TrustedLen iterator's size hint is not exact: {:?}",
36 self.reserve(additional
);
38 let mut ptr
= self.as_mut_ptr().add(self.len());
39 let mut local_len
= SetLenOnDrop
::new(&mut self.len
);
40 iterator
.for_each(move |element
| {
41 ptr
::write(ptr
, element
);
43 // Since the loop executes user code which can panic we have to bump the pointer
45 // NB can't overflow since we would have had to alloc the address space
46 local_len
.increment_len(1);
50 // Per TrustedLen contract a `None` upper bound means that the iterator length
51 // truly exceeds usize::MAX, which would eventually lead to a capacity overflow anyway.
52 // Since the other branch already panics eagerly (via `reserve()`) we do the same here.
53 // This avoids additional codegen for a fallback code path which would eventually
55 panic
!("capacity overflow");
60 impl<T
, A
: Allocator
> SpecExtend
<T
, IntoIter
<T
>> for Vec
<T
, A
> {
61 fn spec_extend(&mut self, mut iterator
: IntoIter
<T
>) {
63 self.append_elements(iterator
.as_slice() as _
);
65 iterator
.forget_remaining_elements();
69 impl<'a
, T
: 'a
, I
, A
: Allocator
+ 'a
> SpecExtend
<&'a T
, I
> for Vec
<T
, A
>
71 I
: Iterator
<Item
= &'a T
>,
74 default fn spec_extend(&mut self, iterator
: I
) {
75 self.spec_extend(iterator
.cloned())
79 impl<'a
, T
: 'a
, A
: Allocator
+ 'a
> SpecExtend
<&'a T
, slice
::Iter
<'a
, T
>> for Vec
<T
, A
>
83 fn spec_extend(&mut self, iterator
: slice
::Iter
<'a
, T
>) {
84 let slice
= iterator
.as_slice();
85 unsafe { self.append_elements(slice) }
;