rust_spec/
drop.rs

1//! Drop behavior classification.
2//!
3//! Drop behavior specifies whether dropping a type runs custom drop code, automatic drop glue,
4//! or both.
5use core::{convert::Infallible, ops::Add};
6
7/// Dropping this type does not run drop glue.
8pub enum NoDrop {}
9
10/// Owned contents need automatic drop glue.
11pub enum AutoDrop {}
12
13/// The type has a custom [`Drop`] implementation, with the given drop behavior for its contents.
14pub struct CustomDrop<I: DropKind>(core::marker::PhantomData<I>, Infallible);
15
16#[sealed::sealed]
17pub trait DropKind {}
18
19#[sealed::sealed]
20impl DropKind for NoDrop {}
21#[sealed::sealed]
22impl DropKind for AutoDrop {}
23#[sealed::sealed]
24impl DropKind for CustomDrop<NoDrop> {}
25#[sealed::sealed]
26impl DropKind for CustomDrop<AutoDrop> {}
27
28impl Add<Self> for NoDrop {
29    type Output = Self;
30
31    fn add(self, _: Self) -> Self::Output {
32        unreachable!()
33    }
34}
35
36impl Add<AutoDrop> for NoDrop {
37    type Output = AutoDrop;
38
39    fn add(self, _: AutoDrop) -> Self::Output {
40        unreachable!()
41    }
42}
43
44impl<I: DropKind> Add<CustomDrop<I>> for NoDrop {
45    type Output = AutoDrop;
46
47    fn add(self, _: CustomDrop<I>) -> Self::Output {
48        unreachable!()
49    }
50}
51
52impl<Rhs> Add<Rhs> for AutoDrop {
53    type Output = Self;
54
55    fn add(self, _: Rhs) -> Self::Output {
56        unreachable!()
57    }
58}
59
60impl Add<NoDrop> for CustomDrop<NoDrop> {
61    type Output = Self;
62
63    fn add(self, _: NoDrop) -> Self::Output {
64        unreachable!()
65    }
66}
67
68impl Add<AutoDrop> for CustomDrop<NoDrop> {
69    type Output = CustomDrop<AutoDrop>;
70
71    fn add(self, _: AutoDrop) -> Self::Output {
72        unreachable!()
73    }
74}
75
76impl<I: DropKind> Add<CustomDrop<I>> for CustomDrop<NoDrop> {
77    type Output = CustomDrop<AutoDrop>;
78
79    fn add(self, _: CustomDrop<I>) -> Self::Output {
80        unreachable!()
81    }
82}
83
84impl<Rhs> Add<Rhs> for CustomDrop<AutoDrop> {
85    type Output = Self;
86
87    fn add(self, _: Rhs) -> Self::Output {
88        unreachable!()
89    }
90}
rust_spec/drop.rs

rust_spec/
drop.rs
