73 lines
1.8 KiB
Rust
73 lines
1.8 KiB
Rust
use crate::stable_hasher::{StableHasher, HashStable};
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/// A vector type optimized for cases where this size is usually 0 (cf. `SmallVector`).
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/// The `Option<Box<..>>` wrapping allows us to represent a zero sized vector with `None`,
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/// which uses only a single (null) pointer.
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#[derive(Clone, RustcEncodable, RustcDecodable, Debug)]
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pub struct ThinVec<T>(Option<Box<Vec<T>>>);
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impl<T> ThinVec<T> {
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pub fn new() -> Self {
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ThinVec(None)
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}
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}
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impl<T> From<Vec<T>> for ThinVec<T> {
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fn from(vec: Vec<T>) -> Self {
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if vec.is_empty() {
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ThinVec(None)
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} else {
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ThinVec(Some(Box::new(vec)))
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}
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}
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}
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impl<T> Into<Vec<T>> for ThinVec<T> {
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fn into(self) -> Vec<T> {
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match self {
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ThinVec(None) => Vec::new(),
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ThinVec(Some(vec)) => *vec,
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}
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}
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}
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impl<T> ::std::ops::Deref for ThinVec<T> {
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type Target = [T];
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fn deref(&self) -> &[T] {
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match *self {
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ThinVec(None) => &[],
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ThinVec(Some(ref vec)) => vec,
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}
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}
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}
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impl<T> ::std::ops::DerefMut for ThinVec<T> {
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fn deref_mut(&mut self) -> &mut [T] {
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match *self {
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ThinVec(None) => &mut [],
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ThinVec(Some(ref mut vec)) => vec,
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}
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}
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}
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impl<T> Extend<T> for ThinVec<T> {
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fn extend<I: IntoIterator<Item = T>>(&mut self, iter: I) {
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match *self {
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ThinVec(Some(ref mut vec)) => vec.extend(iter),
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ThinVec(None) => *self = iter.into_iter().collect::<Vec<_>>().into(),
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}
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}
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}
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impl<T: HashStable<CTX>, CTX> HashStable<CTX> for ThinVec<T> {
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fn hash_stable(&self, hcx: &mut CTX, hasher: &mut StableHasher) {
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(**self).hash_stable(hcx, hasher)
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}
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}
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impl<T> Default for ThinVec<T> {
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fn default() -> Self {
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Self(None)
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}
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}
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