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
|
# `munge`
[![crates.io badge]][crates.io] [![docs badge]][docs] [![license badge]][license]
[crates.io badge]: https://img.shields.io/crates/v/munge.svg
[crates.io]: https://crates.io/crates/munge
[docs badge]: https://img.shields.io/docsrs/munge
[docs]: https://docs.rs/munge
[license badge]: https://img.shields.io/badge/license-MIT-blue.svg
[license]: https://github.com/rkyv/munge/blob/master/LICENSE
Munge makes it easy and safe to destructure `MaybeUninit`s, `Cell`s,
`UnsafeCell`s, `ManuallyDrop`s, and more.
## Documentation
- [munge](https://docs.rs/munge), the core library
- [munge_macro](https://docs.rs/munge_macro), the proc macro at the core of
munge.
## Examples
Initialize `MaybeUninit`s:
```rust
use core::mem::MaybeUninit;
use munge::munge;
pub struct Example {
a: u32,
b: (char, f32),
}
let mut mu = MaybeUninit::<Example>::uninit();
munge!(let Example { a, b: (c, mut f) } = &mut mu);
assert_eq!(a.write(10), &10);
assert_eq!(c.write('x'), &'x');
assert_eq!(f.write(3.14), &3.14);
// Note that `mut` bindings can be reassigned like you'd expect:
f = &mut MaybeUninit::uninit();
// SAFETY: `mu` is completely initialized.
let init = unsafe { mu.assume_init() };
assert_eq!(init.a, 10);
assert_eq!(init.b.0, 'x');
assert_eq!(init.b.1, 3.14);
```
Destructure `Cell`s:
```rust
use core::cell::Cell;
use munge::munge;
pub struct Example {
a: u32,
b: (char, f32),
}
let value = Example {
a: 10,
b: ('x', 3.14),
};
let cell = Cell::<Example>::new(value);
munge!(let Example { a, b: (c, f) } = &cell);
assert_eq!(a.get(), 10);
a.set(42);
assert_eq!(c.get(), 'x');
c.set('!');
assert_eq!(f.get(), 3.14);
f.set(1.41);
let value = cell.into_inner();
assert_eq!(value.a, 42);
assert_eq!(value.b.0, '!');
assert_eq!(value.b.1, 1.41);
```
You can even extend munge to work with your own types by implementing its
`Destructure` and `Restructure` traits:
```rust
use munge::{Destructure, Restructure, Move, munge};
pub struct Invariant<T>(T);
impl<T> Invariant<T> {
/// # Safety
///
/// `value` must uphold my custom invariant.
pub unsafe fn new_unchecked(value: T) -> Self {
Self(value)
}
pub fn unwrap(self) -> T {
self.0
}
}
// SAFETY:
// - `Invariant<T>` is destructured by move, so its `Destructuring` type is
// `Move`.
// - `underlying` returns a pointer to its inner type, so it is guaranteed
// to be non-null, properly aligned, and valid for reads.
unsafe impl<T> Destructure for Invariant<T> {
type Underlying = T;
type Destructuring = Move;
fn underlying(&mut self) -> *mut Self::Underlying {
&mut self.0 as *mut Self::Underlying
}
}
// SAFETY: `restructure` returns an `Invariant<U>` that takes ownership of
// the restructured field because `Invariant<T>` is destructured by move.
unsafe impl<T, U> Restructure<U> for Invariant<T> {
type Restructured = Invariant<U>;
unsafe fn restructure(&self, ptr: *mut U) -> Self::Restructured {
// SAFETY: The caller has guaranteed that `ptr` is a pointer to a
// subfield of some `T`, so it must be properly aligned, valid for
// reads, and initialized. We may move the fields because the
// destructuring type for `Invariant<T>` is `Move`.
let value = unsafe { ptr.read() };
Invariant(value)
}
}
// SAFETY: `(1, 2, 3)` upholds my custom invariant.
let value = unsafe { Invariant::new_unchecked((1, 2, 3)) };
munge!(let (one, two, three) = value);
assert_eq!(one.unwrap(), 1);
assert_eq!(two.unwrap(), 2);
assert_eq!(three.unwrap(), 3);
```
|
