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. `SmallVec`).
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, Hash, Eq, PartialEq)]
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> {
24 pub fn push(&mut self, item: T) {
26 ThinVec(Some(ref mut vec)) => vec.push(item),
27 ThinVec(None) => *self = vec![item].into(),
31 /// Note: if `set_len(0)` is called on a non-empty `ThinVec`, it will
32 /// remain in the `Some` form. This is required for some code sequences
33 /// (such as the one in `flat_map_in_place`) that call `set_len(0)` before
34 /// an operation that might panic, and then call `set_len(n)` again
36 pub unsafe fn set_len(&mut self, new_len: usize) {
39 // A prerequisite of `Vec::set_len` is that `new_len` must be
40 // less than or equal to capacity(). The same applies here.
42 panic!("unsafe ThinVec::set_len({})", new_len);
45 ThinVec(Some(ref mut vec)) => vec.set_len(new_len),
49 pub fn insert(&mut self, index: usize, value: T) {
53 *self = vec![value].into();
55 panic!("invalid ThinVec::insert");
58 ThinVec(Some(ref mut vec)) => vec.insert(index, value),
62 pub fn remove(&mut self, index: usize) -> T {
64 ThinVec(None) => panic!("invalid ThinVec::remove"),
65 ThinVec(Some(vec)) => vec.remove(index),
69 pub fn as_slice(&self) -> &[T] {
72 ThinVec(Some(vec)) => vec.as_slice(),
77 impl<T> From<Vec<T>> for ThinVec<T> {
78 fn from(vec: Vec<T>) -> Self {
79 if vec.is_empty() { ThinVec(None) } else { ThinVec(Some(Box::new(vec))) }
83 impl<T> Into<Vec<T>> for ThinVec<T> {
84 fn into(self) -> Vec<T> {
86 ThinVec(None) => Vec::new(),
87 ThinVec(Some(vec)) => *vec,
92 impl<T> ::std::ops::Deref for ThinVec<T> {
94 fn deref(&self) -> &[T] {
97 ThinVec(Some(ref vec)) => vec,
102 impl<T> ::std::ops::DerefMut for ThinVec<T> {
103 fn deref_mut(&mut self) -> &mut [T] {
105 ThinVec(None) => &mut [],
106 ThinVec(Some(ref mut vec)) => vec,
111 impl<T> FromIterator<T> for ThinVec<T> {
112 fn from_iter<I: IntoIterator<Item = T>>(iter: I) -> Self {
113 // `Vec::from_iter()` should not allocate if the iterator is empty.
114 let vec: Vec<_> = iter.into_iter().collect();
115 if vec.is_empty() { ThinVec(None) } else { ThinVec(Some(Box::new(vec))) }
119 impl<T> IntoIterator for ThinVec<T> {
121 type IntoIter = std::vec::IntoIter<T>;
123 fn into_iter(self) -> Self::IntoIter {
124 // This is still performant because `Vec::new()` does not allocate.
125 self.0.map_or_else(Vec::new, |ptr| *ptr).into_iter()
129 impl<'a, T> IntoIterator for &'a ThinVec<T> {
131 type IntoIter = std::slice::Iter<'a, T>;
133 fn into_iter(self) -> Self::IntoIter {
138 impl<'a, T> IntoIterator for &'a mut ThinVec<T> {
139 type Item = &'a mut T;
140 type IntoIter = std::slice::IterMut<'a, T>;
142 fn into_iter(self) -> Self::IntoIter {
143 self.as_mut().iter_mut()
147 impl<T> Extend<T> for ThinVec<T> {
148 fn extend<I: IntoIterator<Item = T>>(&mut self, iter: I) {
150 ThinVec(Some(ref mut vec)) => vec.extend(iter),
151 ThinVec(None) => *self = iter.into_iter().collect::<Vec<_>>().into(),
155 fn extend_one(&mut self, item: T) {
159 fn extend_reserve(&mut self, additional: usize) {
161 ThinVec(Some(ref mut vec)) => vec.reserve(additional),
162 ThinVec(None) => *self = Vec::with_capacity(additional).into(),
167 impl<T: HashStable<CTX>, CTX> HashStable<CTX> for ThinVec<T> {
168 fn hash_stable(&self, hcx: &mut CTX, hasher: &mut StableHasher) {
169 (**self).hash_stable(hcx, hasher)
173 impl<T> Default for ThinVec<T> {
174 fn default() -> Self {