692 lines
21 KiB
Rust
692 lines
21 KiB
Rust
use core::cell::RefCell;
|
||
use core::ptr;
|
||
use core::ptr::*;
|
||
use std::fmt::{Debug, Display};
|
||
|
||
#[test]
|
||
fn test_const_from_raw_parts() {
|
||
const SLICE: &[u8] = &[1, 2, 3, 4];
|
||
const FROM_RAW: &[u8] = unsafe { &*slice_from_raw_parts(SLICE.as_ptr(), SLICE.len()) };
|
||
assert_eq!(SLICE, FROM_RAW);
|
||
|
||
let slice = &[1, 2, 3, 4, 5];
|
||
let from_raw = unsafe { &*slice_from_raw_parts(slice.as_ptr(), 2) };
|
||
assert_eq!(&slice[..2], from_raw);
|
||
}
|
||
|
||
#[test]
|
||
fn test() {
|
||
unsafe {
|
||
struct Pair {
|
||
fst: isize,
|
||
snd: isize,
|
||
}
|
||
let mut p = Pair { fst: 10, snd: 20 };
|
||
let pptr: *mut Pair = &mut p;
|
||
let iptr: *mut isize = pptr as *mut isize;
|
||
assert_eq!(*iptr, 10);
|
||
*iptr = 30;
|
||
assert_eq!(*iptr, 30);
|
||
assert_eq!(p.fst, 30);
|
||
|
||
*pptr = Pair { fst: 50, snd: 60 };
|
||
assert_eq!(*iptr, 50);
|
||
assert_eq!(p.fst, 50);
|
||
assert_eq!(p.snd, 60);
|
||
|
||
let v0 = vec![32000u16, 32001u16, 32002u16];
|
||
let mut v1 = vec![0u16, 0u16, 0u16];
|
||
|
||
copy(v0.as_ptr().offset(1), v1.as_mut_ptr().offset(1), 1);
|
||
assert!((v1[0] == 0u16 && v1[1] == 32001u16 && v1[2] == 0u16));
|
||
copy(v0.as_ptr().offset(2), v1.as_mut_ptr(), 1);
|
||
assert!((v1[0] == 32002u16 && v1[1] == 32001u16 && v1[2] == 0u16));
|
||
copy(v0.as_ptr(), v1.as_mut_ptr().offset(2), 1);
|
||
assert!((v1[0] == 32002u16 && v1[1] == 32001u16 && v1[2] == 32000u16));
|
||
}
|
||
}
|
||
|
||
#[test]
|
||
fn test_is_null() {
|
||
let p: *const isize = null();
|
||
assert!(p.is_null());
|
||
|
||
let q = p.wrapping_offset(1);
|
||
assert!(!q.is_null());
|
||
|
||
let mp: *mut isize = null_mut();
|
||
assert!(mp.is_null());
|
||
|
||
let mq = mp.wrapping_offset(1);
|
||
assert!(!mq.is_null());
|
||
|
||
// Pointers to unsized types -- slices
|
||
let s: &mut [u8] = &mut [1, 2, 3];
|
||
let cs: *const [u8] = s;
|
||
assert!(!cs.is_null());
|
||
|
||
let ms: *mut [u8] = s;
|
||
assert!(!ms.is_null());
|
||
|
||
let cz: *const [u8] = &[];
|
||
assert!(!cz.is_null());
|
||
|
||
let mz: *mut [u8] = &mut [];
|
||
assert!(!mz.is_null());
|
||
|
||
let ncs: *const [u8] = null::<[u8; 3]>();
|
||
assert!(ncs.is_null());
|
||
|
||
let nms: *mut [u8] = null_mut::<[u8; 3]>();
|
||
assert!(nms.is_null());
|
||
|
||
// Pointers to unsized types -- trait objects
|
||
let ci: *const dyn ToString = &3;
|
||
assert!(!ci.is_null());
|
||
|
||
let mi: *mut dyn ToString = &mut 3;
|
||
assert!(!mi.is_null());
|
||
|
||
let nci: *const dyn ToString = null::<isize>();
|
||
assert!(nci.is_null());
|
||
|
||
let nmi: *mut dyn ToString = null_mut::<isize>();
|
||
assert!(nmi.is_null());
|
||
}
|
||
|
||
#[test]
|
||
fn test_as_ref() {
|
||
unsafe {
|
||
let p: *const isize = null();
|
||
assert_eq!(p.as_ref(), None);
|
||
|
||
let q: *const isize = &2;
|
||
assert_eq!(q.as_ref().unwrap(), &2);
|
||
|
||
let p: *mut isize = null_mut();
|
||
assert_eq!(p.as_ref(), None);
|
||
|
||
let q: *mut isize = &mut 2;
|
||
assert_eq!(q.as_ref().unwrap(), &2);
|
||
|
||
// Lifetime inference
|
||
let u = 2isize;
|
||
{
|
||
let p = &u as *const isize;
|
||
assert_eq!(p.as_ref().unwrap(), &2);
|
||
}
|
||
|
||
// Pointers to unsized types -- slices
|
||
let s: &mut [u8] = &mut [1, 2, 3];
|
||
let cs: *const [u8] = s;
|
||
assert_eq!(cs.as_ref(), Some(&*s));
|
||
|
||
let ms: *mut [u8] = s;
|
||
assert_eq!(ms.as_ref(), Some(&*s));
|
||
|
||
let cz: *const [u8] = &[];
|
||
assert_eq!(cz.as_ref(), Some(&[][..]));
|
||
|
||
let mz: *mut [u8] = &mut [];
|
||
assert_eq!(mz.as_ref(), Some(&[][..]));
|
||
|
||
let ncs: *const [u8] = null::<[u8; 3]>();
|
||
assert_eq!(ncs.as_ref(), None);
|
||
|
||
let nms: *mut [u8] = null_mut::<[u8; 3]>();
|
||
assert_eq!(nms.as_ref(), None);
|
||
|
||
// Pointers to unsized types -- trait objects
|
||
let ci: *const dyn ToString = &3;
|
||
assert!(ci.as_ref().is_some());
|
||
|
||
let mi: *mut dyn ToString = &mut 3;
|
||
assert!(mi.as_ref().is_some());
|
||
|
||
let nci: *const dyn ToString = null::<isize>();
|
||
assert!(nci.as_ref().is_none());
|
||
|
||
let nmi: *mut dyn ToString = null_mut::<isize>();
|
||
assert!(nmi.as_ref().is_none());
|
||
}
|
||
}
|
||
|
||
#[test]
|
||
fn test_as_mut() {
|
||
unsafe {
|
||
let p: *mut isize = null_mut();
|
||
assert!(p.as_mut() == None);
|
||
|
||
let q: *mut isize = &mut 2;
|
||
assert!(q.as_mut().unwrap() == &mut 2);
|
||
|
||
// Lifetime inference
|
||
let mut u = 2isize;
|
||
{
|
||
let p = &mut u as *mut isize;
|
||
assert!(p.as_mut().unwrap() == &mut 2);
|
||
}
|
||
|
||
// Pointers to unsized types -- slices
|
||
let s: &mut [u8] = &mut [1, 2, 3];
|
||
let ms: *mut [u8] = s;
|
||
assert_eq!(ms.as_mut(), Some(&mut [1, 2, 3][..]));
|
||
|
||
let mz: *mut [u8] = &mut [];
|
||
assert_eq!(mz.as_mut(), Some(&mut [][..]));
|
||
|
||
let nms: *mut [u8] = null_mut::<[u8; 3]>();
|
||
assert_eq!(nms.as_mut(), None);
|
||
|
||
// Pointers to unsized types -- trait objects
|
||
let mi: *mut dyn ToString = &mut 3;
|
||
assert!(mi.as_mut().is_some());
|
||
|
||
let nmi: *mut dyn ToString = null_mut::<isize>();
|
||
assert!(nmi.as_mut().is_none());
|
||
}
|
||
}
|
||
|
||
#[test]
|
||
fn test_ptr_addition() {
|
||
unsafe {
|
||
let xs = vec![5; 16];
|
||
let mut ptr = xs.as_ptr();
|
||
let end = ptr.offset(16);
|
||
|
||
while ptr < end {
|
||
assert_eq!(*ptr, 5);
|
||
ptr = ptr.offset(1);
|
||
}
|
||
|
||
let mut xs_mut = xs;
|
||
let mut m_ptr = xs_mut.as_mut_ptr();
|
||
let m_end = m_ptr.offset(16);
|
||
|
||
while m_ptr < m_end {
|
||
*m_ptr += 5;
|
||
m_ptr = m_ptr.offset(1);
|
||
}
|
||
|
||
assert!(xs_mut == vec![10; 16]);
|
||
}
|
||
}
|
||
|
||
#[test]
|
||
fn test_ptr_subtraction() {
|
||
unsafe {
|
||
let xs = vec![0, 1, 2, 3, 4, 5, 6, 7, 8, 9];
|
||
let mut idx = 9;
|
||
let ptr = xs.as_ptr();
|
||
|
||
while idx >= 0 {
|
||
assert_eq!(*(ptr.offset(idx as isize)), idx as isize);
|
||
idx = idx - 1;
|
||
}
|
||
|
||
let mut xs_mut = xs;
|
||
let m_start = xs_mut.as_mut_ptr();
|
||
let mut m_ptr = m_start.offset(9);
|
||
|
||
loop {
|
||
*m_ptr += *m_ptr;
|
||
if m_ptr == m_start {
|
||
break;
|
||
}
|
||
m_ptr = m_ptr.offset(-1);
|
||
}
|
||
|
||
assert_eq!(xs_mut, [0, 2, 4, 6, 8, 10, 12, 14, 16, 18]);
|
||
}
|
||
}
|
||
|
||
#[test]
|
||
fn test_set_memory() {
|
||
let mut xs = [0u8; 20];
|
||
let ptr = xs.as_mut_ptr();
|
||
unsafe {
|
||
write_bytes(ptr, 5u8, xs.len());
|
||
}
|
||
assert!(xs == [5u8; 20]);
|
||
}
|
||
|
||
#[test]
|
||
fn test_set_memory_const() {
|
||
const XS: [u8; 20] = {
|
||
let mut xs = [0u8; 20];
|
||
let ptr = xs.as_mut_ptr();
|
||
unsafe {
|
||
ptr.write_bytes(5u8, xs.len());
|
||
}
|
||
xs
|
||
};
|
||
|
||
assert!(XS == [5u8; 20]);
|
||
}
|
||
|
||
#[test]
|
||
fn test_unsized_nonnull() {
|
||
let xs: &[i32] = &[1, 2, 3];
|
||
let ptr = unsafe { NonNull::new_unchecked(xs as *const [i32] as *mut [i32]) };
|
||
let ys = unsafe { ptr.as_ref() };
|
||
let zs: &[i32] = &[1, 2, 3];
|
||
assert!(ys == zs);
|
||
}
|
||
|
||
#[test]
|
||
fn test_const_nonnull_new() {
|
||
const {
|
||
assert!(NonNull::new(core::ptr::null_mut::<()>()).is_none());
|
||
|
||
let value = &mut 0u32;
|
||
let mut ptr = NonNull::new(value).unwrap();
|
||
unsafe { *ptr.as_mut() = 42 };
|
||
|
||
let reference = unsafe { &*ptr.as_ref() };
|
||
assert!(*reference == *value);
|
||
assert!(*reference == 42);
|
||
};
|
||
}
|
||
|
||
#[test]
|
||
#[allow(warnings)]
|
||
// Have a symbol for the test below. It doesn’t need to be an actual variadic function, match the
|
||
// ABI, or even point to an actual executable code, because the function itself is never invoked.
|
||
#[no_mangle]
|
||
pub fn test_variadic_fnptr() {
|
||
use core::hash::{Hash, SipHasher};
|
||
extern "C" {
|
||
fn test_variadic_fnptr(_: u64, ...) -> f64;
|
||
}
|
||
let p: unsafe extern "C" fn(u64, ...) -> f64 = test_variadic_fnptr;
|
||
let q = p.clone();
|
||
assert_eq!(p, q);
|
||
assert!(!(p < q));
|
||
let mut s = SipHasher::new();
|
||
assert_eq!(p.hash(&mut s), q.hash(&mut s));
|
||
}
|
||
|
||
#[test]
|
||
fn write_unaligned_drop() {
|
||
thread_local! {
|
||
static DROPS: RefCell<Vec<u32>> = RefCell::new(Vec::new());
|
||
}
|
||
|
||
struct Dropper(u32);
|
||
|
||
impl Drop for Dropper {
|
||
fn drop(&mut self) {
|
||
DROPS.with(|d| d.borrow_mut().push(self.0));
|
||
}
|
||
}
|
||
|
||
{
|
||
let c = Dropper(0);
|
||
let mut t = Dropper(1);
|
||
unsafe {
|
||
write_unaligned(&mut t, c);
|
||
}
|
||
}
|
||
DROPS.with(|d| assert_eq!(*d.borrow(), [0]));
|
||
}
|
||
|
||
#[test]
|
||
fn align_offset_zst() {
|
||
// For pointers of stride = 0, the pointer is already aligned or it cannot be aligned at
|
||
// all, because no amount of elements will align the pointer.
|
||
let mut p = 1;
|
||
while p < 1024 {
|
||
assert_eq!((p as *const ()).align_offset(p), 0);
|
||
if p != 1 {
|
||
assert_eq!(((p + 1) as *const ()).align_offset(p), !0);
|
||
}
|
||
p = (p + 1).next_power_of_two();
|
||
}
|
||
}
|
||
|
||
#[test]
|
||
fn align_offset_stride1() {
|
||
// For pointers of stride = 1, the pointer can always be aligned. The offset is equal to
|
||
// number of bytes.
|
||
let mut align = 1;
|
||
while align < 1024 {
|
||
for ptr in 1..2 * align {
|
||
let expected = ptr % align;
|
||
let offset = if expected == 0 { 0 } else { align - expected };
|
||
assert_eq!(
|
||
(ptr as *const u8).align_offset(align),
|
||
offset,
|
||
"ptr = {}, align = {}, size = 1",
|
||
ptr,
|
||
align
|
||
);
|
||
}
|
||
align = (align + 1).next_power_of_two();
|
||
}
|
||
}
|
||
|
||
#[test]
|
||
fn align_offset_weird_strides() {
|
||
#[repr(packed)]
|
||
struct A3(u16, u8);
|
||
struct A4(u32);
|
||
#[repr(packed)]
|
||
struct A5(u32, u8);
|
||
#[repr(packed)]
|
||
struct A6(u32, u16);
|
||
#[repr(packed)]
|
||
struct A7(u32, u16, u8);
|
||
#[repr(packed)]
|
||
struct A8(u32, u32);
|
||
#[repr(packed)]
|
||
struct A9(u32, u32, u8);
|
||
#[repr(packed)]
|
||
struct A10(u32, u32, u16);
|
||
|
||
unsafe fn test_weird_stride<T>(ptr: *const T, align: usize) -> bool {
|
||
let numptr = ptr as usize;
|
||
let mut expected = usize::MAX;
|
||
// Naive but definitely correct way to find the *first* aligned element of stride::<T>.
|
||
for el in 0..align {
|
||
if (numptr + el * ::std::mem::size_of::<T>()) % align == 0 {
|
||
expected = el;
|
||
break;
|
||
}
|
||
}
|
||
let got = ptr.align_offset(align);
|
||
if got != expected {
|
||
eprintln!(
|
||
"aligning {:p} (with stride of {}) to {}, expected {}, got {}",
|
||
ptr,
|
||
::std::mem::size_of::<T>(),
|
||
align,
|
||
expected,
|
||
got
|
||
);
|
||
return true;
|
||
}
|
||
return false;
|
||
}
|
||
|
||
// For pointers of stride != 1, we verify the algorithm against the naivest possible
|
||
// implementation
|
||
let mut align = 1;
|
||
let mut x = false;
|
||
// Miri is too slow
|
||
let limit = if cfg!(miri) { 32 } else { 1024 };
|
||
while align < limit {
|
||
for ptr in 1usize..4 * align {
|
||
unsafe {
|
||
x |= test_weird_stride::<A3>(ptr as *const A3, align);
|
||
x |= test_weird_stride::<A4>(ptr as *const A4, align);
|
||
x |= test_weird_stride::<A5>(ptr as *const A5, align);
|
||
x |= test_weird_stride::<A6>(ptr as *const A6, align);
|
||
x |= test_weird_stride::<A7>(ptr as *const A7, align);
|
||
x |= test_weird_stride::<A8>(ptr as *const A8, align);
|
||
x |= test_weird_stride::<A9>(ptr as *const A9, align);
|
||
x |= test_weird_stride::<A10>(ptr as *const A10, align);
|
||
}
|
||
}
|
||
align = (align + 1).next_power_of_two();
|
||
}
|
||
assert!(!x);
|
||
}
|
||
|
||
#[test]
|
||
fn offset_from() {
|
||
let mut a = [0; 5];
|
||
let ptr1: *mut i32 = &mut a[1];
|
||
let ptr2: *mut i32 = &mut a[3];
|
||
unsafe {
|
||
assert_eq!(ptr2.offset_from(ptr1), 2);
|
||
assert_eq!(ptr1.offset_from(ptr2), -2);
|
||
assert_eq!(ptr1.offset(2), ptr2);
|
||
assert_eq!(ptr2.offset(-2), ptr1);
|
||
}
|
||
}
|
||
|
||
#[test]
|
||
fn ptr_metadata() {
|
||
struct Unit;
|
||
struct Pair<A, B: ?Sized>(A, B);
|
||
extern "C" {
|
||
type Extern;
|
||
}
|
||
let () = metadata(&());
|
||
let () = metadata(&Unit);
|
||
let () = metadata(&4_u32);
|
||
let () = metadata(&String::new());
|
||
let () = metadata(&Some(4_u32));
|
||
let () = metadata(&ptr_metadata);
|
||
let () = metadata(&|| {});
|
||
let () = metadata(&[4, 7]);
|
||
let () = metadata(&(4, String::new()));
|
||
let () = metadata(&Pair(4, String::new()));
|
||
let () = metadata(0 as *const Extern);
|
||
let () = metadata(0 as *const <&u32 as std::ops::Deref>::Target);
|
||
|
||
assert_eq!(metadata("foo"), 3_usize);
|
||
assert_eq!(metadata(&[4, 7][..]), 2_usize);
|
||
|
||
let dst_tuple: &(bool, [u8]) = &(true, [0x66, 0x6F, 0x6F]);
|
||
let dst_struct: &Pair<bool, [u8]> = &Pair(true, [0x66, 0x6F, 0x6F]);
|
||
assert_eq!(metadata(dst_tuple), 3_usize);
|
||
assert_eq!(metadata(dst_struct), 3_usize);
|
||
unsafe {
|
||
let dst_tuple: &(bool, str) = std::mem::transmute(dst_tuple);
|
||
let dst_struct: &Pair<bool, str> = std::mem::transmute(dst_struct);
|
||
assert_eq!(&dst_tuple.1, "foo");
|
||
assert_eq!(&dst_struct.1, "foo");
|
||
assert_eq!(metadata(dst_tuple), 3_usize);
|
||
assert_eq!(metadata(dst_struct), 3_usize);
|
||
}
|
||
|
||
let vtable_1: DynMetadata<dyn Debug> = metadata(&4_u16 as &dyn Debug);
|
||
let vtable_2: DynMetadata<dyn Display> = metadata(&4_u16 as &dyn Display);
|
||
let vtable_3: DynMetadata<dyn Display> = metadata(&4_u32 as &dyn Display);
|
||
let vtable_4: DynMetadata<dyn Display> = metadata(&(true, 7_u32) as &(bool, dyn Display));
|
||
let vtable_5: DynMetadata<dyn Display> =
|
||
metadata(&Pair(true, 7_u32) as &Pair<bool, dyn Display>);
|
||
unsafe {
|
||
let address_1: usize = std::mem::transmute(vtable_1);
|
||
let address_2: usize = std::mem::transmute(vtable_2);
|
||
let address_3: usize = std::mem::transmute(vtable_3);
|
||
let address_4: usize = std::mem::transmute(vtable_4);
|
||
let address_5: usize = std::mem::transmute(vtable_5);
|
||
// Different trait => different vtable pointer
|
||
assert_ne!(address_1, address_2);
|
||
// Different erased type => different vtable pointer
|
||
assert_ne!(address_2, address_3);
|
||
// Same erased type and same trait => same vtable pointer
|
||
assert_eq!(address_3, address_4);
|
||
assert_eq!(address_3, address_5);
|
||
}
|
||
}
|
||
|
||
#[test]
|
||
fn ptr_metadata_bounds() {
|
||
fn metadata_eq_method_address<T: ?Sized>() -> usize {
|
||
// The `Metadata` associated type has an `Ord` bound, so this is valid:
|
||
<<T as Pointee>::Metadata as PartialEq>::eq as usize
|
||
}
|
||
// "Synthetic" trait impls generated by the compiler like those of `Pointee`
|
||
// are not checked for bounds of associated type.
|
||
// So with a buggy libcore we could have both:
|
||
// * `<dyn Display as Pointee>::Metadata == DynMetadata`
|
||
// * `DynMetadata: !PartialEq`
|
||
// … and cause an ICE here:
|
||
metadata_eq_method_address::<dyn Display>();
|
||
|
||
// For this reason, let’s check here that bounds are satisfied:
|
||
|
||
let _ = static_assert_expected_bounds_for_metadata::<()>;
|
||
let _ = static_assert_expected_bounds_for_metadata::<usize>;
|
||
let _ = static_assert_expected_bounds_for_metadata::<DynMetadata<dyn Display>>;
|
||
fn _static_assert_associated_type<T: ?Sized>() {
|
||
let _ = static_assert_expected_bounds_for_metadata::<<T as Pointee>::Metadata>;
|
||
}
|
||
|
||
fn static_assert_expected_bounds_for_metadata<Meta>()
|
||
where
|
||
// Keep this in sync with the associated type in `library/core/src/ptr/metadata.rs`
|
||
Meta: Copy + Send + Sync + Ord + std::hash::Hash + Unpin,
|
||
{
|
||
}
|
||
}
|
||
|
||
#[test]
|
||
fn dyn_metadata() {
|
||
#[derive(Debug)]
|
||
#[repr(align(32))]
|
||
struct Something([u8; 47]);
|
||
|
||
let value = Something([0; 47]);
|
||
let trait_object: &dyn Debug = &value;
|
||
let meta = metadata(trait_object);
|
||
|
||
assert_eq!(meta.size_of(), 64);
|
||
assert_eq!(meta.size_of(), std::mem::size_of::<Something>());
|
||
assert_eq!(meta.align_of(), 32);
|
||
assert_eq!(meta.align_of(), std::mem::align_of::<Something>());
|
||
assert_eq!(meta.layout(), std::alloc::Layout::new::<Something>());
|
||
|
||
assert!(format!("{:?}", meta).starts_with("DynMetadata(0x"));
|
||
}
|
||
|
||
#[test]
|
||
fn from_raw_parts() {
|
||
let mut value = 5_u32;
|
||
let address = &mut value as *mut _ as *mut ();
|
||
let trait_object: &dyn Display = &mut value;
|
||
let vtable = metadata(trait_object);
|
||
let trait_object = NonNull::from(trait_object);
|
||
|
||
assert_eq!(ptr::from_raw_parts(address, vtable), trait_object.as_ptr());
|
||
assert_eq!(ptr::from_raw_parts_mut(address, vtable), trait_object.as_ptr());
|
||
assert_eq!(NonNull::from_raw_parts(NonNull::new(address).unwrap(), vtable), trait_object);
|
||
|
||
let mut array = [5_u32, 5, 5, 5, 5];
|
||
let address = &mut array as *mut _ as *mut ();
|
||
let array_ptr = NonNull::from(&mut array);
|
||
let slice_ptr = NonNull::from(&mut array[..]);
|
||
|
||
assert_eq!(ptr::from_raw_parts(address, ()), array_ptr.as_ptr());
|
||
assert_eq!(ptr::from_raw_parts_mut(address, ()), array_ptr.as_ptr());
|
||
assert_eq!(NonNull::from_raw_parts(NonNull::new(address).unwrap(), ()), array_ptr);
|
||
|
||
assert_eq!(ptr::from_raw_parts(address, 5), slice_ptr.as_ptr());
|
||
assert_eq!(ptr::from_raw_parts_mut(address, 5), slice_ptr.as_ptr());
|
||
assert_eq!(NonNull::from_raw_parts(NonNull::new(address).unwrap(), 5), slice_ptr);
|
||
}
|
||
|
||
#[test]
|
||
fn thin_box() {
|
||
let foo = ThinBox::<dyn Display>::new(4);
|
||
assert_eq!(foo.to_string(), "4");
|
||
drop(foo);
|
||
let bar = ThinBox::<dyn Display>::new(7);
|
||
assert_eq!(bar.to_string(), "7");
|
||
|
||
// A slightly more interesting library that could be built on top of metadata APIs.
|
||
//
|
||
// * It could be generalized to any `T: ?Sized` (not just trait object)
|
||
// if `{size,align}_of_for_meta<T: ?Sized>(T::Metadata)` are added.
|
||
// * Constructing a `ThinBox` without consuming and deallocating a `Box`
|
||
// requires either the unstable `Unsize` marker trait,
|
||
// or the unstable `unsized_locals` language feature,
|
||
// or taking `&dyn T` and restricting to `T: Copy`.
|
||
|
||
use std::alloc::*;
|
||
use std::marker::PhantomData;
|
||
|
||
struct ThinBox<T>
|
||
where
|
||
T: ?Sized + Pointee<Metadata = DynMetadata<T>>,
|
||
{
|
||
ptr: NonNull<DynMetadata<T>>,
|
||
phantom: PhantomData<T>,
|
||
}
|
||
|
||
impl<T> ThinBox<T>
|
||
where
|
||
T: ?Sized + Pointee<Metadata = DynMetadata<T>>,
|
||
{
|
||
pub fn new<Value: std::marker::Unsize<T>>(value: Value) -> Self {
|
||
let unsized_: &T = &value;
|
||
let meta = metadata(unsized_);
|
||
let meta_layout = Layout::for_value(&meta);
|
||
let value_layout = Layout::for_value(&value);
|
||
let (layout, offset) = meta_layout.extend(value_layout).unwrap();
|
||
// `DynMetadata` is pointer-sized:
|
||
assert!(layout.size() > 0);
|
||
// If `ThinBox<T>` is generalized to any `T: ?Sized`,
|
||
// handle ZSTs with a dangling pointer without going through `alloc()`,
|
||
// like `Box<T>` does.
|
||
unsafe {
|
||
let ptr = NonNull::new(alloc(layout))
|
||
.unwrap_or_else(|| handle_alloc_error(layout))
|
||
.cast::<DynMetadata<T>>();
|
||
ptr.as_ptr().write(meta);
|
||
ptr.cast::<u8>().as_ptr().add(offset).cast::<Value>().write(value);
|
||
Self { ptr, phantom: PhantomData }
|
||
}
|
||
}
|
||
|
||
fn meta(&self) -> DynMetadata<T> {
|
||
unsafe { *self.ptr.as_ref() }
|
||
}
|
||
|
||
fn layout(&self) -> (Layout, usize) {
|
||
let meta = self.meta();
|
||
Layout::for_value(&meta).extend(meta.layout()).unwrap()
|
||
}
|
||
|
||
fn value_ptr(&self) -> *const T {
|
||
let (_, offset) = self.layout();
|
||
let data_ptr = unsafe { self.ptr.cast::<u8>().as_ptr().add(offset) };
|
||
ptr::from_raw_parts(data_ptr.cast(), self.meta())
|
||
}
|
||
|
||
fn value_mut_ptr(&mut self) -> *mut T {
|
||
let (_, offset) = self.layout();
|
||
// FIXME: can this line be shared with the same in `value_ptr()`
|
||
// without upsetting Stacked Borrows?
|
||
let data_ptr = unsafe { self.ptr.cast::<u8>().as_ptr().add(offset) };
|
||
from_raw_parts_mut(data_ptr.cast(), self.meta())
|
||
}
|
||
}
|
||
|
||
impl<T> std::ops::Deref for ThinBox<T>
|
||
where
|
||
T: ?Sized + Pointee<Metadata = DynMetadata<T>>,
|
||
{
|
||
type Target = T;
|
||
|
||
fn deref(&self) -> &T {
|
||
unsafe { &*self.value_ptr() }
|
||
}
|
||
}
|
||
|
||
impl<T> std::ops::DerefMut for ThinBox<T>
|
||
where
|
||
T: ?Sized + Pointee<Metadata = DynMetadata<T>>,
|
||
{
|
||
fn deref_mut(&mut self) -> &mut T {
|
||
unsafe { &mut *self.value_mut_ptr() }
|
||
}
|
||
}
|
||
|
||
impl<T> std::ops::Drop for ThinBox<T>
|
||
where
|
||
T: ?Sized + Pointee<Metadata = DynMetadata<T>>,
|
||
{
|
||
fn drop(&mut self) {
|
||
let (layout, _) = self.layout();
|
||
unsafe {
|
||
drop_in_place::<T>(&mut **self);
|
||
dealloc(self.ptr.cast().as_ptr(), layout);
|
||
}
|
||
}
|
||
}
|
||
}
|