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// run-pass
#![feature(control_flow_enum)]
#![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::Awesome(u) => match u {},
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 {
Ok(v) => match v {}
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::Awesome(u) => match u {},
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();
}
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