1 use crate::stable_hasher::{HashStable, StableHasher};
3 use std::iter::FromIterator;
5 /// A vector type optimized for cases where this size is usually 0 (cf. `SmallVector`).
6 /// The `Option<Box<..>>` wrapping allows us to represent a zero sized vector with `None`,
7 /// which uses only a single (null) pointer.
8 #[derive(Clone, Encodable, Decodable, Debug)]
9 pub struct ThinVec<T>(Option<Box<Vec<T>>>);
12 pub fn new() -> Self {
16 pub fn iter(&self) -> std::slice::Iter<'_, T> {
20 pub fn iter_mut(&mut self) -> std::slice::IterMut<'_, T> {
25 impl<T> From<Vec<T>> for ThinVec<T> {
26 fn from(vec: Vec<T>) -> Self {
27 if vec.is_empty() { ThinVec(None) } else { ThinVec(Some(Box::new(vec))) }
31 impl<T> Into<Vec<T>> for ThinVec<T> {
32 fn into(self) -> Vec<T> {
34 ThinVec(None) => Vec::new(),
35 ThinVec(Some(vec)) => *vec,
40 impl<T> ::std::ops::Deref for ThinVec<T> {
42 fn deref(&self) -> &[T] {
45 ThinVec(Some(ref vec)) => vec,
50 impl<T> ::std::ops::DerefMut for ThinVec<T> {
51 fn deref_mut(&mut self) -> &mut [T] {
53 ThinVec(None) => &mut [],
54 ThinVec(Some(ref mut vec)) => vec,
59 impl<T> FromIterator<T> for ThinVec<T> {
60 fn from_iter<I: IntoIterator<Item = T>>(iter: I) -> Self {
61 // `Vec::from_iter()` should not allocate if the iterator is empty.
62 let vec: Vec<_> = iter.into_iter().collect();
63 if vec.is_empty() { ThinVec(None) } else { ThinVec(Some(Box::new(vec))) }
67 impl<T> IntoIterator for ThinVec<T> {
69 type IntoIter = std::vec::IntoIter<T>;
71 fn into_iter(self) -> Self::IntoIter {
72 // This is still performant because `Vec::new()` does not allocate.
73 self.0.map_or_else(Vec::new, |ptr| *ptr).into_iter()
77 impl<'a, T> IntoIterator for &'a ThinVec<T> {
79 type IntoIter = std::slice::Iter<'a, T>;
81 fn into_iter(self) -> Self::IntoIter {
86 impl<'a, T> IntoIterator for &'a mut ThinVec<T> {
87 type Item = &'a mut T;
88 type IntoIter = std::slice::IterMut<'a, T>;
90 fn into_iter(self) -> Self::IntoIter {
91 self.as_mut().iter_mut()
95 impl<T> Extend<T> for ThinVec<T> {
96 fn extend<I: IntoIterator<Item = T>>(&mut self, iter: I) {
98 ThinVec(Some(ref mut vec)) => vec.extend(iter),
99 ThinVec(None) => *self = iter.into_iter().collect::<Vec<_>>().into(),
103 fn extend_one(&mut self, item: T) {
105 ThinVec(Some(ref mut vec)) => vec.push(item),
106 ThinVec(None) => *self = vec![item].into(),
110 fn extend_reserve(&mut self, additional: usize) {
112 ThinVec(Some(ref mut vec)) => vec.reserve(additional),
113 ThinVec(None) => *self = Vec::with_capacity(additional).into(),
118 impl<T: HashStable<CTX>, CTX> HashStable<CTX> for ThinVec<T> {
119 fn hash_stable(&self, hcx: &mut CTX, hasher: &mut StableHasher) {
120 (**self).hash_stable(hcx, hasher)
124 impl<T> Default for ThinVec<T> {
125 fn default() -> Self {