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// run-pass
#[derive(Copy, Clone, Debug, PartialEq)]
struct BadNumErr;
fn try_num(x: i32) -> Result<i32, BadNumErr> {
if x <= 5 {
Ok(x + 1)
} else {
Err(BadNumErr)
}
}
type ResOpt = Result<Option<i32>, BadNumErr>;
type OptRes = Option<Result<i32, BadNumErr>>;
fn main() {
let mut x: ResOpt = Ok(Some(5));
let mut y: OptRes = Some(Ok(5));
assert_eq!(x, y.transpose());
assert_eq!(x.transpose(), y);
x = Ok(None);
y = None;
assert_eq!(x, y.transpose());
assert_eq!(x.transpose(), y);
x = Err(BadNumErr);
y = Some(Err(BadNumErr));
assert_eq!(x, y.transpose());
assert_eq!(x.transpose(), y);
let res: Result<Vec<i32>, BadNumErr> =
(0..10)
.map(|x| {
let y = try_num(x)?;
Ok(if y % 2 == 0 {
Some(y - 1)
} else {
None
})
})
.filter_map(Result::transpose)
.collect();
assert_eq!(res, Err(BadNumErr))
}
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