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October 25, 2018 08:37
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#![feature(unsize)] | |
use std::alloc::Layout; | |
use std::marker::{PhantomData, Unsize}; | |
use std::mem; | |
/// Assumes pointer-sized metadata | |
#[repr(C)] | |
struct DstPointerRepr { | |
data: *mut (), | |
meta: *mut (), | |
} | |
pub struct VecOfDst<DST: ?Sized> { | |
storage: heterogeneous_vec::HeterogeneousVec, | |
_phantom: PhantomData<DST>, | |
} | |
impl<DST: ?Sized> VecOfDst<DST> { | |
pub fn new() -> Self { | |
Self { | |
storage: heterogeneous_vec::HeterogeneousVec::new(), | |
_phantom: PhantomData, | |
} | |
} | |
pub fn push<T: Unsize<DST>>(&mut self, value: T) { | |
assert_eq!(mem::size_of::<&DST>(), | |
mem::size_of::<DstPointerRepr>()); | |
let repr = unsafe { | |
let dst_ref: &DST = &value; | |
mem::transmute_copy::<&DST, DstPointerRepr>(&dst_ref) | |
}; | |
self.storage.push(repr.meta); | |
self.storage.push(value); | |
} | |
pub fn iter(&self) -> impl Iterator<Item=&DST> { | |
self.iter_raw().map(|ptr| unsafe { &*ptr }) | |
} | |
pub fn iter_mut(&mut self) -> impl Iterator<Item=&mut DST> { | |
self.iter_raw().map(|ptr| unsafe { &mut *ptr }) | |
} | |
fn iter_raw<'a>(&'a self) -> impl Iterator<Item=*mut DST> + 'a { | |
struct Iter<'a, DST: ?Sized> { | |
iter: heterogeneous_vec::Iter<'a>, | |
_phantom: PhantomData<DST>, | |
} | |
impl<'a, DST: ?Sized> Iterator for Iter<'a, DST> { | |
type Item = *mut DST; | |
fn next(&mut self) -> Option<Self::Item> { | |
const POINTER_BYTES: usize = mem::size_of::<*mut ()>(); | |
const POINTER_BITS: usize = POINTER_BYTES * 8; | |
const HYPER_ALIGNED: *mut () = (1_usize << (POINTER_BITS - 1)) as _; | |
unsafe { | |
self.iter.read_next::<*mut ()>().map(|meta| { | |
let fake_repr = DstPointerRepr { data: HYPER_ALIGNED, meta }; | |
let fake_ref = mem::transmute_copy::<DstPointerRepr, &DST>(&fake_repr); | |
let data = self.iter.next(Layout::for_value(fake_ref)).unwrap(); | |
let repr = DstPointerRepr { data, meta }; | |
mem::transmute_copy::<DstPointerRepr, *mut DST>(&repr) | |
}) | |
} | |
} | |
} | |
Iter { | |
iter: self.storage.iter(), | |
_phantom: PhantomData, | |
} | |
} | |
} | |
impl<DST: ?Sized> Drop for VecOfDst<DST> { | |
fn drop(&mut self) { | |
for item in self.iter_raw() { | |
unsafe { | |
item.drop_in_place() | |
} | |
} | |
} | |
} | |
#[test] | |
fn trait_objets() { | |
#[repr(align(1024))] | |
#[derive(Debug)] | |
struct SuperAligned(u32); | |
let mut v = VecOfDst::<std::fmt::Debug>::new(); | |
v.push(4); | |
v.push(SuperAligned(7)); | |
v.push("foo"); | |
assert_eq!(debugs(v.iter()), ["4", "SuperAligned(7)", "\"foo\""]); | |
} | |
#[test] | |
fn slices() { | |
let mut v = VecOfDst::<[u32]>::new(); | |
v.push([4]); | |
v.push([9000, 1, 3]); | |
assert_eq!(debugs(v.iter()), ["[4]", "[9000, 1, 3]"]); | |
} | |
#[cfg(test)] | |
fn debugs<I>(iter: I) -> Vec<String> | |
where I: Iterator, I::Item: std::fmt::Debug | |
{ | |
iter.map(|x| format!("{:?}", x)).collect() | |
} | |
mod heterogeneous_vec { | |
use std::alloc::{self, Layout}; | |
use std::mem; | |
use std::num::NonZeroUsize; | |
use std::ptr; | |
pub struct HeterogeneousVec { | |
ptr: *mut u8, | |
// In bytes: | |
len: usize, | |
capacity: usize, | |
align: NonZeroUsize, | |
} | |
unsafe fn realloc_with_align(ptr: *mut u8, old_layout: Layout, new_layout: Layout) | |
-> *mut u8 { | |
if new_layout.align() == old_layout.align() { | |
alloc::realloc(ptr, old_layout, new_layout.size()) | |
} else { | |
let new_ptr = alloc::alloc(new_layout); | |
if !new_ptr.is_null() { | |
let size = old_layout.size().min(new_layout.size()); | |
ptr::copy_nonoverlapping(ptr, new_ptr, size); | |
alloc::dealloc(ptr, old_layout); | |
} | |
new_ptr | |
} | |
} | |
fn align_to(position: usize, align: usize) -> usize { | |
let remainder = position % align; | |
if remainder > 0 { | |
position.checked_add(align - remainder).unwrap() | |
} else { | |
position | |
} | |
} | |
impl HeterogeneousVec { | |
pub fn new() -> Self { | |
Self { | |
ptr: ptr::null_mut(), | |
len: 0, | |
capacity: 0, | |
align: NonZeroUsize::new(1).unwrap(), | |
} | |
} | |
pub fn push<T>(&mut self, value: T) { | |
let value_size = mem::size_of::<T>(); | |
let value_align = mem::align_of::<T>(); | |
let value_position = align_to(self.len, value_align); | |
let available = self.capacity.saturating_sub(value_position); | |
let align = self.align.get(); | |
if available < value_size || align < value_align { | |
let required_capacity = self.len.checked_add(value_size).unwrap(); | |
let new_capacity = self.capacity.max(required_capacity).next_power_of_two(); | |
let new_align = align.max(value_align); | |
let new_layout = Layout::from_size_align(new_capacity, new_align).unwrap(); | |
let ptr = unsafe { | |
if self.ptr.is_null() { | |
alloc::alloc(new_layout) | |
} else { | |
let old_layout = Layout::from_size_align(self.capacity, align).unwrap(); | |
realloc_with_align(self.ptr, old_layout, new_layout) | |
} | |
}; | |
if ptr.is_null() { | |
alloc::handle_alloc_error(new_layout) | |
} | |
self.ptr = ptr; | |
self.capacity = new_capacity; | |
} | |
unsafe { | |
let next = self.ptr.add(value_position) as *mut T; | |
debug_assert!(next as usize % value_align == 0); | |
next.write(value); | |
} | |
self.len = value_position + value_size; | |
} | |
pub fn iter(&self) -> Iter { | |
Iter { vec: self, position: 0 } | |
} | |
} | |
pub struct Iter<'a> { | |
vec: &'a HeterogeneousVec, | |
position: usize, | |
} | |
impl<'a> Iter<'a> { | |
pub unsafe fn read_next<T>(&mut self) -> Option<T> { | |
self.next(Layout::new::<T>()).map(|ptr| (ptr as *mut T).read()) | |
} | |
pub unsafe fn next(&mut self, layout: Layout) -> Option<*mut ()> { | |
if self.position < self.vec.len { | |
let value_position = align_to(self.position, layout.align()); | |
let ptr = self.vec.ptr.add(value_position); | |
self.position = value_position + layout.size(); | |
debug_assert!(self.position <= self.vec.len); | |
Some(ptr as *mut ()) | |
} else { | |
None | |
} | |
} | |
} | |
} |
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