src/librustc_data_structures/array_vec.rs

   1 // Copyright 2016 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 //! A stack-allocated vector, allowing storage of N elements on the stack.
  12 //!
  13 //! Currently, only the N = 8 case is supported (due to Array only being impl-ed for [T; 8]).
  14
  15 use std::marker::Unsize;
  16 use std::iter::Extend;
  17 use std::ptr::drop_in_place;
  18 use std::ops::{Deref, DerefMut};
  19 use std::slice;
  20 use std::fmt;
  21
  22 pub unsafe trait Array {
  23     type Element;
  24     type PartialStorage: Default + Unsize<[ManuallyDrop<Self::Element>]>;
  25     const LEN: usize;
  26 }
  27
  28 unsafe impl<T> Array for [T; 8] {
  29     type Element = T;
  30     type PartialStorage = [ManuallyDrop<T>; 8];
  31     const LEN: usize = 8;
  32 }
  33
  34 pub struct ArrayVec<A: Array> {
  35     count: usize,
  36     values: A::PartialStorage
  37 }
  38
  39 impl<A: Array> ArrayVec<A> {
  40     pub fn new() -> Self {
  41         ArrayVec {
  42             count: 0,
  43             values: Default::default(),
  44         }
  45     }
  46 }
  47
  48 impl<A> fmt::Debug for ArrayVec<A>
  49     where A: Array,
  50           A::Element: fmt::Debug {
  51     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
  52         self[..].fmt(f)
  53     }
  54 }
  55
  56 impl<A: Array> Deref for ArrayVec<A> {
  57     type Target = [A::Element];
  58     fn deref(&self) -> &Self::Target {
  59         unsafe {
  60             slice::from_raw_parts(&self.values as *const _ as *const A::Element, self.count)
  61         }
  62     }
  63 }
  64
  65 impl<A: Array> DerefMut for ArrayVec<A> {
  66     fn deref_mut(&mut self) -> &mut [A::Element] {
  67         unsafe {
  68             slice::from_raw_parts_mut(&mut self.values as *mut _ as *mut A::Element, self.count)
  69         }
  70     }
  71 }
  72
  73 impl<A: Array> Drop for ArrayVec<A> {
  74     fn drop(&mut self) {
  75         unsafe {
  76             drop_in_place(&mut self[..])
  77         }
  78     }
  79 }
  80
  81 impl<A: Array> Extend<A::Element> for ArrayVec<A> {
  82     fn extend<I>(&mut self, iter: I) where I: IntoIterator<Item=A::Element> {
  83         for el in iter {
  84             unsafe {
  85                 let arr = &mut self.values as &mut [ManuallyDrop<_>];
  86                 arr[self.count].value = el;
  87             }
  88             self.count += 1;
  89         }
  90     }
  91 }
  92
  93 // FIXME: This should use repr(transparent) from rust-lang/rfcs#1758.
  94 #[allow(unions_with_drop_fields)]
  95 pub union ManuallyDrop<T> {
  96     value: T,
  97     #[allow(dead_code)]
  98     empty: (),
  99 }
 100
 101 impl<T> Default for ManuallyDrop<T> {
 102     fn default() -> Self {
 103         ManuallyDrop { empty: () }
 104     }
 105 }
 106