1 use crate::stable_hasher
::{HashStable, StableHasher}
;
3 /// A vector type optimized for cases where this size is usually 0 (cf. `SmallVector`).
4 /// The `Option<Box<..>>` wrapping allows us to represent a zero sized vector with `None`,
5 /// which uses only a single (null) pointer.
6 #[derive(Clone, Encodable, Decodable, Debug)]
7 pub struct ThinVec
<T
>(Option
<Box
<Vec
<T
>>>);
10 pub fn new() -> Self {
15 impl<T
> From
<Vec
<T
>> for ThinVec
<T
> {
16 fn from(vec
: Vec
<T
>) -> Self {
17 if vec
.is_empty() { ThinVec(None) }
else { ThinVec(Some(Box::new(vec))) }
21 impl<T
> Into
<Vec
<T
>> for ThinVec
<T
> {
22 fn into(self) -> Vec
<T
> {
24 ThinVec(None
) => Vec
::new(),
25 ThinVec(Some(vec
)) => *vec
,
30 impl<T
> ::std
::ops
::Deref
for ThinVec
<T
> {
32 fn deref(&self) -> &[T
] {
35 ThinVec(Some(ref vec
)) => vec
,
40 impl<T
> ::std
::ops
::DerefMut
for ThinVec
<T
> {
41 fn deref_mut(&mut self) -> &mut [T
] {
43 ThinVec(None
) => &mut [],
44 ThinVec(Some(ref mut vec
)) => vec
,
49 impl<T
> Extend
<T
> for ThinVec
<T
> {
50 fn extend
<I
: IntoIterator
<Item
= T
>>(&mut self, iter
: I
) {
52 ThinVec(Some(ref mut vec
)) => vec
.extend(iter
),
53 ThinVec(None
) => *self = iter
.into_iter().collect
::<Vec
<_
>>().into(),
57 fn extend_one(&mut self, item
: T
) {
59 ThinVec(Some(ref mut vec
)) => vec
.push(item
),
60 ThinVec(None
) => *self = vec
![item
].into(),
64 fn extend_reserve(&mut self, additional
: usize) {
66 ThinVec(Some(ref mut vec
)) => vec
.reserve(additional
),
67 ThinVec(None
) => *self = Vec
::with_capacity(additional
).into(),
72 impl<T
: HashStable
<CTX
>, CTX
> HashStable
<CTX
> for ThinVec
<T
> {
73 fn hash_stable(&self, hcx
: &mut CTX
, hasher
: &mut StableHasher
) {
74 (**self).hash_stable(hcx
, hasher
)
78 impl<T
> Default
for ThinVec
<T
> {
79 fn default() -> Self {