checked_rs/
guard.rs

1use crate::view::Validator;
2use std::{
3    marker::PhantomData,
4    mem::{ManuallyDrop, MaybeUninit},
5};
6
7#[derive(Debug)]
8pub struct Guard<'a, T: 'static, E, U: Validator<Item = T, Error = E>>(
9    pub(crate) MaybeUninit<T>,
10    pub(crate) &'a mut T,
11    pub(crate) PhantomData<U>,
12);
13
14impl<'a, T, E, U: Validator<Item = T, Error = E>> std::ops::Deref for Guard<'a, T, E, U> {
15    type Target = T;
16
17    #[inline(always)]
18    fn deref(&self) -> &Self::Target {
19        unsafe { self.0.assume_init_ref() }
20    }
21}
22
23impl<'a, T, E, U: Validator<Item = T, Error = E>> std::ops::DerefMut for Guard<'a, T, E, U> {
24    #[inline(always)]
25    fn deref_mut(&mut self) -> &mut Self::Target {
26        unsafe { self.0.assume_init_mut() }
27    }
28}
29
30impl<'a, T, E, U: Validator<Item = T, Error = E>> AsRef<T> for Guard<'a, T, E, U> {
31    #[inline(always)]
32    fn as_ref(&self) -> &T {
33        unsafe { self.0.assume_init_ref() }
34    }
35}
36
37impl<'a, T, E, U: Validator<Item = T, Error = E>> AsMut<T> for Guard<'a, T, E, U> {
38    #[inline(always)]
39    fn as_mut(&mut self) -> &mut T {
40        unsafe { self.0.assume_init_mut() }
41    }
42}
43
44impl<'a, T, E, U: Validator<Item = T, Error = E>> Drop for Guard<'a, T, E, U> {
45    fn drop(&mut self) {
46        #[cfg(debug_assertions)]
47        {
48            eprintln!("A `Guard` was dropped without calling `commit` or `discard` first");
49        }
50    }
51}
52
53impl<'a, T, E, U: Validator<Item = T, Error = E>> Guard<'a, T, E, U> {
54    #[inline(always)]
55    pub(super) fn new(dst: &'a mut T) -> Self {
56        Self(
57            MaybeUninit::new(unsafe { std::ptr::read(&*dst) }),
58            dst,
59            PhantomData,
60        )
61    }
62
63    #[inline(always)]
64    pub fn is_changed(&self) -> bool
65    where
66        T: PartialEq,
67    {
68        let a = unsafe { self.0.assume_init_ref() };
69        let b = &*self.1;
70
71        a != b
72    }
73
74    #[inline(always)]
75    pub fn check(&self) -> Result<(), E> {
76        U::validate(unsafe { self.0.assume_init_ref() })
77    }
78
79    #[inline(always)]
80    pub fn commit(self) -> Result<(), Self> {
81        let mut this = std::mem::ManuallyDrop::new(self);
82
83        match this.check() {
84            Ok(_) => {
85                *this.1 = unsafe { this.0.assume_init_read() };
86                Ok(())
87            }
88            Err(_) => Err(ManuallyDrop::into_inner(this)),
89        }
90    }
91
92    #[inline(always)]
93    pub fn discard(self) {
94        std::mem::forget(self);
95    }
96}
97
98#[macro_export]
99macro_rules! commit_or_bail {
100    ($guard:expr) => {
101        match $guard.check() {
102            Ok(_) => {
103                $guard.commit().unwrap();
104            }
105            Err(e) => {
106                return Err(e.into());
107            }
108        }
109    };
110}
checked_rs/guard.rs

checked_rs/
guard.rs
