1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
|
//! Implement Fallible Box
use super::TryClone;
use crate::TryReserveError;
use alloc::alloc::Layout;
use alloc::boxed::Box;
use core::borrow::Borrow;
use core::ops::Deref;
use core::ptr::NonNull;
/// trait to implement Fallible Box
pub trait FallibleBox<T> {
/// try creating a new box, returning a Result<Box<T>,
/// TryReserveError> if allocation failed
fn try_new(t: T) -> Result<Self, TryReserveError>
where
Self: Sized;
}
/// TryBox is a thin wrapper around alloc::boxed::Box to provide support for
/// fallible allocation.
///
/// See the crate documentation for more.
pub struct TryBox<T> {
inner: Box<T>,
}
impl<T> TryBox<T> {
#[inline]
pub fn try_new(t: T) -> Result<Self, TryReserveError> {
Ok(Self {
inner: <Box<T> as FallibleBox<T>>::try_new(t)?,
})
}
#[inline(always)]
pub fn into_raw(b: TryBox<T>) -> *mut T {
Box::into_raw(b.inner)
}
/// # Safety
///
/// See std::boxed::from_raw
#[inline(always)]
pub unsafe fn from_raw(raw: *mut T) -> Self {
Self {
inner: Box::from_raw(raw),
}
}
}
impl<T: TryClone> TryClone for TryBox<T> {
fn try_clone(&self) -> Result<Self, TryReserveError> {
let clone: T = (*self.inner).try_clone()?;
Self::try_new(clone)
}
}
impl<T> Deref for TryBox<T> {
type Target = T;
#[inline(always)]
fn deref(&self) -> &T {
self.inner.deref()
}
}
fn alloc(layout: Layout) -> Result<NonNull<u8>, TryReserveError> {
#[cfg(feature = "unstable")] // requires allocator_api
{
use core::alloc::Allocator;
alloc::alloc::Global
.allocate(layout)
.map_err(|_e| TryReserveError::AllocError {
layout,
#[cfg(not(feature = "rust_1_57"))]
non_exhaustive: (),
})
.map(|v| v.cast())
}
#[cfg(not(feature = "unstable"))]
{
match layout.size() {
0 => {
// Required for alloc safety
// See https://doc.rust-lang.org/stable/std/alloc/trait.GlobalAlloc.html#safety-1
Ok(NonNull::dangling())
}
1..=core::usize::MAX => {
let ptr = unsafe { alloc::alloc::alloc(layout) };
core::ptr::NonNull::new(ptr).ok_or(TryReserveError::AllocError { layout })
}
_ => unreachable!("size must be non-negative"),
}
}
}
impl<T> FallibleBox<T> for Box<T> {
fn try_new(t: T) -> Result<Self, TryReserveError> {
let layout = Layout::for_value(&t);
let ptr = alloc(layout)?.as_ptr() as *mut T;
unsafe {
core::ptr::write(ptr, t);
Ok(Box::from_raw(ptr))
}
}
}
impl<T: TryClone> TryClone for Box<T> {
#[inline]
fn try_clone(&self) -> Result<Self, TryReserveError> {
<Self as FallibleBox<T>>::try_new(Borrow::<T>::borrow(self).try_clone()?)
}
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn boxed() {
let mut v = <Box<_> as FallibleBox<_>>::try_new(5).unwrap();
assert_eq!(*v, 5);
*v = 3;
assert_eq!(*v, 3);
}
// #[test]
// fn big_alloc() {
// let layout = Layout::from_size_align(1_000_000_000_000, 8).unwrap();
// let ptr = unsafe { alloc::alloc::alloc(layout) };
// assert!(ptr.is_null());
// }
#[test]
fn trybox_zst() {
let b = <Box<_> as FallibleBox<_>>::try_new(()).expect("ok");
assert_eq!(b, Box::new(()));
}
struct NonCopyType;
#[test]
fn trybox_deref() {
let try_box: TryBox<NonCopyType> = TryBox::try_new(NonCopyType {}).unwrap();
let _derefed: &NonCopyType = try_box.deref();
}
#[test]
fn trybox_as_deref() {
let try_box_option: Option<TryBox<NonCopyType>> =
Some(TryBox::try_new(NonCopyType).unwrap());
let _ref_option: Option<&NonCopyType> = try_box_option.as_deref();
}
}
|
