use std::alloc::{self, Layout};
use std::marker::PhantomData;
use std::mem;
use std::ops::{Deref, DerefMut};
use std::ptr::{self, NonNull};
struct RawVec<T> {
ptr: NonNull<T>,
cap: usize,
}
unsafe impl<T: Send> Send for RawVec<T> {}
unsafe impl<T: Sync> Sync for RawVec<T> {}
impl<T> RawVec<T> {
fn new() -> Self {
// !0 is usize::MAX. This branch should be stripped at compile time.
let cap = if mem::size_of::<T>() == 0 { !0 } else { 0 };
// `NonNull::dangling()` doubles as "unallocated" and "zero-sized allocation"
RawVec {
ptr: NonNull::dangling(),
cap,
}
}
fn grow(&mut self) {
// since we set the capacity to usize::MAX when T has size 0,
// getting to here necessarily means the Vec is overfull.
assert!(mem::size_of::<T>() != 0, "capacity overflow");
let (new_cap, new_layout) = if self.cap == 0 {
(1, Layout::array::<T>(1).unwrap())
} else {
// This can't overflow because we ensure self.cap <= isize::MAX.
let new_cap = 2 * self.cap;
// `Layout::array` checks that the number of bytes is <= usize::MAX,
// but this is redundant since old_layout.size() <= isize::MAX,
// so the `unwrap` should never fail.
let new_layout = Layout::array::<T>(new_cap).unwrap();
(new_cap, new_layout)
};
// Ensure that the new allocation doesn't exceed `isize::MAX` bytes.
assert!(
new_layout.size() <= isize::MAX as usize,
"Allocation too large"
);
let new_ptr = if self.cap == 0 {
unsafe { alloc::alloc(new_layout) }
} else {
let old_layout = Layout::array::<T>(self.cap).unwrap();
let old_ptr = self.ptr.as_ptr() as *mut u8;
unsafe { alloc::realloc(old_ptr, old_layout, new_layout.size()) }
};
// If allocation fails, `new_ptr` will be null, in which case we abort.
self.ptr = match NonNull::new(new_ptr as *mut T) {
Some(p) => p,
None => alloc::handle_alloc_error(new_layout),
};
self.cap = new_cap;
}
}
impl<T> Drop for RawVec<T> {
fn drop(&mut self) {
let elem_size = mem::size_of::<T>();
if self.cap != 0 && elem_size != 0 {
unsafe {
alloc::dealloc(
self.ptr.as_ptr() as *mut u8,
Layout::array::<T>(self.cap).unwrap(),
);
}
}
}
}
pub struct Vec<T> {
buf: RawVec<T>,
len: usize,
}
impl<T> Vec<T> {
fn ptr(&self) -> *mut T {
self.buf.ptr.as_ptr()
}
fn cap(&self) -> usize {
self.buf.cap
}
pub fn new() -> Self {
Vec {
buf: RawVec::new(),
len: 0,
}
}
pub fn push(&mut self, elem: T) {
if self.len == self.cap() {
self.buf.grow();
}
unsafe {
ptr::write(self.ptr().add(self.len), elem);
}
// Can't overflow, we'll OOM first.
self.len += 1;
}
pub fn pop(&mut self) -> Option<T> {
if self.len == 0 {
None
} else {
self.len -= 1;
unsafe { Some(ptr::read(self.ptr().add(self.len))) }
}
}
pub fn insert(&mut self, index: usize, elem: T) {
assert!(index <= self.len, "index out of bounds");
if self.len == self.cap() {
self.buf.grow();
}
unsafe {
ptr::copy(
self.ptr().add(index),
self.ptr().add(index + 1),
self.len - index,
);
ptr::write(self.ptr().add(index), elem);
}
self.len += 1;
}
pub fn remove(&mut self, index: usize) -> T {
assert!(index < self.len, "index out of bounds");
self.len -= 1;
unsafe {
let result = ptr::read(self.ptr().add(index));
ptr::copy(
self.ptr().add(index + 1),
self.ptr().add(index),
self.len - index,
);
result
}
}
pub fn drain(&mut self) -> Drain<T> {
let iter = unsafe { RawValIter::new(&self) };
// this is a mem::forget safety thing. If Drain is forgotten, we just
// leak the whole Vec's contents. Also we need to do this *eventually*
// anyway, so why not do it now?
self.len = 0;
Drain {
iter,
vec: PhantomData,
}
}
}
impl<T> Drop for Vec<T> {
fn drop(&mut self) {
while let Some(_) = self.pop() {}
// deallocation is handled by RawVec
}
}
impl<T> Deref for Vec<T> {
type Target = [T];
fn deref(&self) -> &[T] {
unsafe { std::slice::from_raw_parts(self.ptr(), self.len) }
}
}
impl<T> DerefMut for Vec<T> {
fn deref_mut(&mut self) -> &mut [T] {
unsafe { std::slice::from_raw_parts_mut(self.ptr(), self.len) }
}
}
impl<T> IntoIterator for Vec<T> {
type Item = T;
type IntoIter = IntoIter<T>;
fn into_iter(self) -> IntoIter<T> {
let (iter, buf) = unsafe {
(RawValIter::new(&self), ptr::read(&self.buf))
};
mem::forget(self);
IntoIter {
iter,
_buf: buf,
}
}
}
struct RawValIter<T> {
start: *const T,
end: *const T,
}
impl<T> RawValIter<T> {
unsafe fn new(slice: &[T]) -> Self {
RawValIter {
start: slice.as_ptr(),
end: if mem::size_of::<T>() == 0 {
((slice.as_ptr() as usize) + slice.len()) as *const _
} else if slice.len() == 0 {
slice.as_ptr()
} else {
slice.as_ptr().add(slice.len())
},
}
}
}
impl<T> Iterator for RawValIter<T> {
type Item = T;
fn next(&mut self) -> Option<T> {
if self.start == self.end {
None
} else {
unsafe {
if mem::size_of::<T>() == 0 {
self.start = (self.start as usize + 1) as *const _;
Some(ptr::read(NonNull::<T>::dangling().as_ptr()))
} else {
let old_ptr = self.start;
self.start = self.start.offset(1);
Some(ptr::read(old_ptr))
}
}
}
}
fn size_hint(&self) -> (usize, Option<usize>) {
let elem_size = mem::size_of::<T>();
let len = (self.end as usize - self.start as usize)
/ if elem_size == 0 { 1 } else { elem_size };
(len, Some(len))
}
}
impl<T> DoubleEndedIterator for RawValIter<T> {
fn next_back(&mut self) -> Option<T> {
if self.start == self.end {
None
} else {
unsafe {
if mem::size_of::<T>() == 0 {
self.end = (self.end as usize - 1) as *const _;
Some(ptr::read(NonNull::<T>::dangling().as_ptr()))
} else {
self.end = self.end.offset(-1);
Some(ptr::read(self.end))
}
}
}
}
}
pub struct IntoIter<T> {
_buf: RawVec<T>, // we don't actually care about this. Just need it to live.
iter: RawValIter<T>,
}
impl<T> Iterator for IntoIter<T> {
type Item = T;
fn next(&mut self) -> Option<T> {
self.iter.next()
}
fn size_hint(&self) -> (usize, Option<usize>) {
self.iter.size_hint()
}
}
impl<T> DoubleEndedIterator for IntoIter<T> {
fn next_back(&mut self) -> Option<T> {
self.iter.next_back()
}
}
impl<T> Drop for IntoIter<T> {
fn drop(&mut self) {
for _ in &mut *self {}
}
}
pub struct Drain<'a, T: 'a> {
vec: PhantomData<&'a mut Vec<T>>,
iter: RawValIter<T>,
}
impl<'a, T> Iterator for Drain<'a, T> {
type Item = T;
fn next(&mut self) -> Option<T> {
self.iter.next()
}
fn size_hint(&self) -> (usize, Option<usize>) {
self.iter.size_hint()
}
}
impl<'a, T> DoubleEndedIterator for Drain<'a, T> {
fn next_back(&mut self) -> Option<T> {
self.iter.next_back()
}
}
impl<'a, T> Drop for Drain<'a, T> {
fn drop(&mut self) {
// pre-drain the iter
for _ in &mut *self {}
}
}
fn main() {
tests::create_push_pop();
tests::iter_test();
tests::test_drain();
tests::test_zst();
println!("All tests finished OK");
}
mod tests {
use super::*;
pub fn create_push_pop() {
let mut v = Vec::new();
v.push(1);
assert_eq!(1, v.len());
assert_eq!(1, v[0]);
for i in v.iter_mut() {
*i += 1;
}
v.insert(0, 5);
let x = v.pop();
assert_eq!(Some(2), x);
assert_eq!(1, v.len());
v.push(10);
let x = v.remove(0);
assert_eq!(5, x);
assert_eq!(1, v.len());
}
pub fn iter_test() {
let mut v = Vec::new();
for i in 0..10 {
v.push(Box::new(i))
}
let mut iter = v.into_iter();
let first = iter.next().unwrap();
let last = iter.next_back().unwrap();
drop(iter);
assert_eq!(0, *first);
assert_eq!(9, *last);
}
pub fn test_drain() {
let mut v = Vec::new();
for i in 0..10 {
v.push(Box::new(i))
}
{
let mut drain = v.drain();
let first = drain.next().unwrap();
let last = drain.next_back().unwrap();
assert_eq!(0, *first);
assert_eq!(9, *last);
}
assert_eq!(0, v.len());
v.push(Box::new(1));
assert_eq!(1, *v.pop().unwrap());
}
pub fn test_zst() {
let mut v = Vec::new();
for _i in 0..10 {
v.push(())
}
let mut count = 0;
for _ in v.into_iter() {
count += 1
}
assert_eq!(10, count);
}
}