vendor/rustc-ap-rustc_data_structures/src/thin_vec.rs

   1 use crate::stable_hasher::{HashStable, StableHasher};
   2
   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, Encodable, Decodable, Debug)]
   7 pub struct ThinVec<T>(Option<Box<Vec<T>>>);
   8
   9 impl<T> ThinVec<T> {
  10     pub fn new() -> Self {
  11         ThinVec(None)
  12     }
  13 }
  14
  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))) }
  18     }
  19 }
  20
  21 impl<T> Into<Vec<T>> for ThinVec<T> {
  22     fn into(self) -> Vec<T> {
  23         match self {
  24             ThinVec(None) => Vec::new(),
  25             ThinVec(Some(vec)) => *vec,
  26         }
  27     }
  28 }
  29
  30 impl<T> ::std::ops::Deref for ThinVec<T> {
  31     type Target = [T];
  32     fn deref(&self) -> &[T] {
  33         match *self {
  34             ThinVec(None) => &[],
  35             ThinVec(Some(ref vec)) => vec,
  36         }
  37     }
  38 }
  39
  40 impl<T> ::std::ops::DerefMut for ThinVec<T> {
  41     fn deref_mut(&mut self) -> &mut [T] {
  42         match *self {
  43             ThinVec(None) => &mut [],
  44             ThinVec(Some(ref mut vec)) => vec,
  45         }
  46     }
  47 }
  48
  49 impl<T> Extend<T> for ThinVec<T> {
  50     fn extend<I: IntoIterator<Item = T>>(&mut self, iter: I) {
  51         match *self {
  52             ThinVec(Some(ref mut vec)) => vec.extend(iter),
  53             ThinVec(None) => *self = iter.into_iter().collect::<Vec<_>>().into(),
  54         }
  55     }
  56
  57     fn extend_one(&mut self, item: T) {
  58         match *self {
  59             ThinVec(Some(ref mut vec)) => vec.push(item),
  60             ThinVec(None) => *self = vec![item].into(),
  61         }
  62     }
  63
  64     fn extend_reserve(&mut self, additional: usize) {
  65         match *self {
  66             ThinVec(Some(ref mut vec)) => vec.reserve(additional),
  67             ThinVec(None) => *self = Vec::with_capacity(additional).into(),
  68         }
  69     }
  70 }
  71
  72 impl<T: HashStable<CTX>, CTX> HashStable<CTX> for ThinVec<T> {
  73     fn hash_stable(&self, hcx: &mut CTX, hasher: &mut StableHasher) {
  74         (**self).hash_stable(hcx, hasher)
  75     }
  76 }
  77
  78 impl<T> Default for ThinVec<T> {
  79     fn default() -> Self {
  80         Self(None)
  81     }
  82 }