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use crate::stable_hasher::{HashStable, StableHasher};
use std::iter::FromIterator;
/// A vector type optimized for cases where this size is usually 0 (cf. `SmallVec`).
/// The `Option<Box<..>>` wrapping allows us to represent a zero sized vector with `None`,
/// which uses only a single (null) pointer.
#[derive(Clone, Encodable, Decodable, Debug, Hash, Eq, PartialEq)]
pub struct ThinVec<T>(Option<Box<Vec<T>>>);
impl<T> ThinVec<T> {
pub fn new() -> Self {
ThinVec(None)
}
pub fn iter(&self) -> std::slice::Iter<'_, T> {
self.into_iter()
}
pub fn iter_mut(&mut self) -> std::slice::IterMut<'_, T> {
self.into_iter()
}
pub fn push(&mut self, item: T) {
match *self {
ThinVec(Some(ref mut vec)) => vec.push(item),
ThinVec(None) => *self = vec![item].into(),
}
}
}
impl<T> From<Vec<T>> for ThinVec<T> {
fn from(vec: Vec<T>) -> Self {
if vec.is_empty() { ThinVec(None) } else { ThinVec(Some(Box::new(vec))) }
}
}
impl<T> Into<Vec<T>> for ThinVec<T> {
fn into(self) -> Vec<T> {
match self {
ThinVec(None) => Vec::new(),
ThinVec(Some(vec)) => *vec,
}
}
}
impl<T> ::std::ops::Deref for ThinVec<T> {
type Target = [T];
fn deref(&self) -> &[T] {
match *self {
ThinVec(None) => &[],
ThinVec(Some(ref vec)) => vec,
}
}
}
impl<T> ::std::ops::DerefMut for ThinVec<T> {
fn deref_mut(&mut self) -> &mut [T] {
match *self {
ThinVec(None) => &mut [],
ThinVec(Some(ref mut vec)) => vec,
}
}
}
impl<T> FromIterator<T> for ThinVec<T> {
fn from_iter<I: IntoIterator<Item = T>>(iter: I) -> Self {
// `Vec::from_iter()` should not allocate if the iterator is empty.
let vec: Vec<_> = iter.into_iter().collect();
if vec.is_empty() { ThinVec(None) } else { ThinVec(Some(Box::new(vec))) }
}
}
impl<T> IntoIterator for ThinVec<T> {
type Item = T;
type IntoIter = std::vec::IntoIter<T>;
fn into_iter(self) -> Self::IntoIter {
// This is still performant because `Vec::new()` does not allocate.
self.0.map_or_else(Vec::new, |ptr| *ptr).into_iter()
}
}
impl<'a, T> IntoIterator for &'a ThinVec<T> {
type Item = &'a T;
type IntoIter = std::slice::Iter<'a, T>;
fn into_iter(self) -> Self::IntoIter {
self.as_ref().iter()
}
}
impl<'a, T> IntoIterator for &'a mut ThinVec<T> {
type Item = &'a mut T;
type IntoIter = std::slice::IterMut<'a, T>;
fn into_iter(self) -> Self::IntoIter {
self.as_mut().iter_mut()
}
}
impl<T> Extend<T> for ThinVec<T> {
fn extend<I: IntoIterator<Item = T>>(&mut self, iter: I) {
match *self {
ThinVec(Some(ref mut vec)) => vec.extend(iter),
ThinVec(None) => *self = iter.into_iter().collect::<Vec<_>>().into(),
}
}
fn extend_one(&mut self, item: T) {
self.push(item)
}
fn extend_reserve(&mut self, additional: usize) {
match *self {
ThinVec(Some(ref mut vec)) => vec.reserve(additional),
ThinVec(None) => *self = Vec::with_capacity(additional).into(),
}
}
}
impl<T: HashStable<CTX>, CTX> HashStable<CTX> for ThinVec<T> {
fn hash_stable(&self, hcx: &mut CTX, hasher: &mut StableHasher) {
(**self).hash_stable(hcx, hasher)
}
}
impl<T> Default for ThinVec<T> {
fn default() -> Self {
Self(None)
}
}
#[cfg(test)]
mod tests;
|
