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, RustcEncodable, RustcDecodable, 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(),
58 impl<T: HashStable<CTX>, CTX> HashStable<CTX> for ThinVec<T> {
59 fn hash_stable(&self, hcx: &mut CTX, hasher: &mut StableHasher) {
60 (**self).hash_stable(hcx, hasher)
64 impl<T> Default for ThinVec<T> {
65 fn default() -> Self {