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
|
//@ run-pass
#![feature(try_trait_v2)]
use std::ops::{ControlFlow, FromResidual, Try};
enum MyResult<T, U> {
Awesome(T),
Terrible(U)
}
enum Never {}
impl<U, V> Try for MyResult<U, V> {
type Output = U;
type Residual = MyResult<Never, V>;
fn from_output(u: U) -> MyResult<U, V> {
MyResult::Awesome(u)
}
fn branch(self) -> ControlFlow<Self::Residual, Self::Output> {
match self {
MyResult::Awesome(u) => ControlFlow::Continue(u),
MyResult::Terrible(e) => ControlFlow::Break(MyResult::Terrible(e)),
}
}
}
impl<U, V, W> FromResidual<MyResult<Never, V>> for MyResult<U, W> where V: Into<W> {
fn from_residual(x: MyResult<Never, V>) -> Self {
match x {
MyResult::Terrible(e) => MyResult::Terrible(e.into()),
}
}
}
type ResultResidual<E> = Result<std::convert::Infallible, E>;
impl<U, V, W> FromResidual<ResultResidual<V>> for MyResult<U, W> where V: Into<W> {
fn from_residual(x: ResultResidual<V>) -> Self {
match x {
Err(e) => MyResult::Terrible(e.into()),
}
}
}
impl<U, V, W> FromResidual<MyResult<Never, V>> for Result<U, W> where V: Into<W> {
fn from_residual(x: MyResult<Never, V>) -> Self {
match x {
MyResult::Terrible(e) => Err(e.into()),
}
}
}
fn f(x: i32) -> Result<i32, String> {
if x == 0 {
Ok(42)
} else {
let y = g(x)?;
Ok(y)
}
}
fn g(x: i32) -> MyResult<i32, String> {
let _y = f(x - 1)?;
MyResult::Terrible("Hello".to_owned())
}
fn h() -> MyResult<i32, String> {
let a: Result<i32, &'static str> = Err("Hello");
let b = a?;
MyResult::Awesome(b)
}
fn i() -> MyResult<i32, String> {
let a: MyResult<i32, &'static str> = MyResult::Terrible("Hello");
let b = a?;
MyResult::Awesome(b)
}
fn main() {
assert!(f(0) == Ok(42));
assert!(f(10) == Err("Hello".to_owned()));
let _ = h();
let _ = i();
}
|
