1 | use core::intrinsics; |
2 | use core::mem; |
3 | use core::ptr; |
4 | |
5 | /// This replaces the value behind the `v` unique reference by calling the |
6 | /// relevant function. |
7 | /// |
8 | /// If a panic occurs in the `change` closure, the entire process will be aborted. |
9 | #[allow (dead_code)] // keep as illustration and for future use |
10 | #[inline ] |
11 | pub fn take_mut<T>(v: &mut T, change: impl FnOnce(T) -> T) { |
12 | replace(v, |value: T| (change(value), ())) |
13 | } |
14 | |
15 | /// This replaces the value behind the `v` unique reference by calling the |
16 | /// relevant function, and returns a result obtained along the way. |
17 | /// |
18 | /// If a panic occurs in the `change` closure, the entire process will be aborted. |
19 | #[inline ] |
20 | pub fn replace<T, R>(v: &mut T, change: impl FnOnce(T) -> (T, R)) -> R { |
21 | struct PanicGuard; |
22 | impl Drop for PanicGuard { |
23 | fn drop(&mut self) { |
24 | intrinsics::abort() |
25 | } |
26 | } |
27 | let guard: PanicGuard = PanicGuard; |
28 | let value: T = unsafe { ptr::read(src:v) }; |
29 | let (new_value: T, ret: R) = change(value); |
30 | unsafe { |
31 | ptr::write(dst:v, src:new_value); |
32 | } |
33 | mem::forget(guard); |
34 | ret |
35 | } |
36 | |