src/libsyntax/util/small_vector.rs

   1 // Copyright 2013-2014 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 use self::SmallVectorRepr::*;
  12 use self::IntoIterRepr::*;
  13
  14 use std::iter::{IntoIterator, FromIterator};
  15 use std::mem;
  16 use std::slice;
  17 use std::vec;
  18
  19 use fold::MoveMap;
  20
  21 /// A vector type optimized for cases where the size is almost always 0 or 1
  22 pub struct SmallVector<T> {
  23     repr: SmallVectorRepr<T>,
  24 }
  25
  26 enum SmallVectorRepr<T> {
  27     Zero,
  28     One(T),
  29     Many(Vec<T>),
  30 }
  31
  32 impl<T> FromIterator<T> for SmallVector<T> {
  33     fn from_iter<I: IntoIterator<Item=T>>(iter: I) -> SmallVector<T> {
  34         let mut v = SmallVector::zero();
  35         v.extend(iter);
  36         v
  37     }
  38 }
  39
  40 impl<T> Extend<T> for SmallVector<T> {
  41     fn extend<I: IntoIterator<Item=T>>(&mut self, iter: I) {
  42         for val in iter {
  43             self.push(val);
  44         }
  45     }
  46 }
  47
  48 impl<T> SmallVector<T> {
  49     pub fn zero() -> SmallVector<T> {
  50         SmallVector { repr: Zero }
  51     }
  52
  53     pub fn one(v: T) -> SmallVector<T> {
  54         SmallVector { repr: One(v) }
  55     }
  56
  57     pub fn many(vs: Vec<T>) -> SmallVector<T> {
  58         SmallVector { repr: Many(vs) }
  59     }
  60
  61     pub fn as_slice<'a>(&'a self) -> &'a [T] {
  62         match self.repr {
  63             Zero => {
  64                 let result: &[T] = &[];
  65                 result
  66             }
  67             One(ref v) => slice::ref_slice(v),
  68             Many(ref vs) => vs
  69         }
  70     }
  71
  72     pub fn push(&mut self, v: T) {
  73         match self.repr {
  74             Zero => self.repr = One(v),
  75             One(..) => {
  76                 let one = mem::replace(&mut self.repr, Zero);
  77                 match one {
  78                     One(v1) => mem::replace(&mut self.repr, Many(vec!(v1, v))),
  79                     _ => unreachable!()
  80                 };
  81             }
  82             Many(ref mut vs) => vs.push(v)
  83         }
  84     }
  85
  86     pub fn push_all(&mut self, other: SmallVector<T>) {
  87         for v in other.into_iter() {
  88             self.push(v);
  89         }
  90     }
  91
  92     pub fn get<'a>(&'a self, idx: usize) -> &'a T {
  93         match self.repr {
  94             One(ref v) if idx == 0 => v,
  95             Many(ref vs) => &vs[idx],
  96             _ => panic!("out of bounds access")
  97         }
  98     }
  99
 100     pub fn expect_one(self, err: &'static str) -> T {
 101         match self.repr {
 102             One(v) => v,
 103             Many(v) => {
 104                 if v.len() == 1 {
 105                     v.into_iter().next().unwrap()
 106                 } else {
 107                     panic!(err)
 108                 }
 109             }
 110             _ => panic!(err)
 111         }
 112     }
 113
 114     /// Deprecated: use `into_iter`.
 115     #[unstable(feature = "rustc_private")]
 116     #[deprecated(since = "1.0.0", reason = "use into_iter")]
 117     pub fn move_iter(self) -> IntoIter<T> {
 118         self.into_iter()
 119     }
 120
 121     pub fn into_iter(self) -> IntoIter<T> {
 122         let repr = match self.repr {
 123             Zero => ZeroIterator,
 124             One(v) => OneIterator(v),
 125             Many(vs) => ManyIterator(vs.into_iter())
 126         };
 127         IntoIter { repr: repr }
 128     }
 129
 130     pub fn len(&self) -> usize {
 131         match self.repr {
 132             Zero => 0,
 133             One(..) => 1,
 134             Many(ref vals) => vals.len()
 135         }
 136     }
 137
 138     pub fn is_empty(&self) -> bool { self.len() == 0 }
 139 }
 140
 141 pub struct IntoIter<T> {
 142     repr: IntoIterRepr<T>,
 143 }
 144
 145 enum IntoIterRepr<T> {
 146     ZeroIterator,
 147     OneIterator(T),
 148     ManyIterator(vec::IntoIter<T>),
 149 }
 150
 151 impl<T> Iterator for IntoIter<T> {
 152     type Item = T;
 153
 154     fn next(&mut self) -> Option<T> {
 155         match self.repr {
 156             ZeroIterator => None,
 157             OneIterator(..) => {
 158                 let mut replacement = ZeroIterator;
 159                 mem::swap(&mut self.repr, &mut replacement);
 160                 match replacement {
 161                     OneIterator(v) => Some(v),
 162                     _ => unreachable!()
 163                 }
 164             }
 165             ManyIterator(ref mut inner) => inner.next()
 166         }
 167     }
 168
 169     fn size_hint(&self) -> (usize, Option<usize>) {
 170         match self.repr {
 171             ZeroIterator => (0, Some(0)),
 172             OneIterator(..) => (1, Some(1)),
 173             ManyIterator(ref inner) => inner.size_hint()
 174         }
 175     }
 176 }
 177
 178 impl<T> MoveMap<T> for SmallVector<T> {
 179     fn move_map<F>(self, mut f: F) -> SmallVector<T> where F: FnMut(T) -> T {
 180         let repr = match self.repr {
 181             Zero => Zero,
 182             One(v) => One(f(v)),
 183             Many(vs) => Many(vs.move_map(f))
 184         };
 185         SmallVector { repr: repr }
 186     }
 187 }
 188
 189 #[cfg(test)]
 190 mod test {
 191     use super::*;
 192
 193     #[test]
 194     fn test_len() {
 195         let v: SmallVector<isize> = SmallVector::zero();
 196         assert_eq!(0, v.len());
 197
 198         assert_eq!(1, SmallVector::one(1).len());
 199         assert_eq!(5, SmallVector::many(vec![1, 2, 3, 4, 5]).len());
 200     }
 201
 202     #[test]
 203     fn test_push_get() {
 204         let mut v = SmallVector::zero();
 205         v.push(1);
 206         assert_eq!(1, v.len());
 207         assert_eq!(&1, v.get(0));
 208         v.push(2);
 209         assert_eq!(2, v.len());
 210         assert_eq!(&2, v.get(1));
 211         v.push(3);
 212         assert_eq!(3, v.len());
 213         assert_eq!(&3, v.get(2));
 214     }
 215
 216     #[test]
 217     fn test_from_iter() {
 218         let v: SmallVector<isize> = (vec![1, 2, 3]).into_iter().collect();
 219         assert_eq!(3, v.len());
 220         assert_eq!(&1, v.get(0));
 221         assert_eq!(&2, v.get(1));
 222         assert_eq!(&3, v.get(2));
 223     }
 224
 225     #[test]
 226     fn test_move_iter() {
 227         let v = SmallVector::zero();
 228         let v: Vec<isize> = v.into_iter().collect();
 229         assert_eq!(v, Vec::new());
 230
 231         let v = SmallVector::one(1);
 232         assert_eq!(v.into_iter().collect::<Vec<_>>(), [1]);
 233
 234         let v = SmallVector::many(vec![1, 2, 3]);
 235         assert_eq!(v.into_iter().collect::<Vec<_>>(), [1, 2, 3]);
 236     }
 237
 238     #[test]
 239     #[should_panic]
 240     fn test_expect_one_zero() {
 241         let _: isize = SmallVector::zero().expect_one("");
 242     }
 243
 244     #[test]
 245     #[should_panic]
 246     fn test_expect_one_many() {
 247         SmallVector::many(vec!(1, 2)).expect_one("");
 248     }
 249
 250     #[test]
 251     fn test_expect_one_one() {
 252         assert_eq!(1, SmallVector::one(1).expect_one(""));
 253         assert_eq!(1, SmallVector::many(vec!(1)).expect_one(""));
 254     }
 255 }