88 lines
1.9 KiB
Rust
88 lines
1.9 KiB
Rust
//@ 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();
|
|
}
|