3 unstable releases
0.4.1 | Aug 20, 2024 |
---|---|
0.4.0 | Jul 27, 2023 |
0.3.0 | Aug 10, 2022 |
22,265 downloads per month
Used in 43 crates
(via munge)
14KB
228 lines
munge
Munge makes it easy and safe to destructure MaybeUninit
s, Cell
s,
UnsafeCell
s, ManuallyDrop
s, and more.
Documentation
- munge, the core library
- munge_macro, the proc macro at the core of munge.
Examples
Initialize MaybeUninit
s:
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:
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:
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);
Dependencies
~260–710KB
~17K SLoC