Just a pondering.on result<(),T>

scottmcm · 2018-10-19T00:59:49.485Z

newpavlov:

You could define your custom enum for your parsing library and impl Try for it, so you will be able to use ? , it will be a somewhat questionable approach, but it will be much-much-much less wrong than using Result and significantly less confusing.

I tried writing iterator methods based on try_fold using Err for “found” and confused myself enough that I added a new enum and Try impl to make things clearer:

github.com

rust-lang/rust/blob/45088b11f55e57a65fa1ebcf6e3b6014152eb516/src/libcore/iter/mod.rs#L358-L379


/// Used to make try_fold closures more like normal loops
#[derive(PartialEq)]
enum LoopState<C, B> {
Continue(C),
Break(B),
}


impl<C, B> Try for LoopState<C, B> {
type Ok = C;
type Error = B;
#[inline]
fn into_result(self) -> Result<Self::Ok, Self::Error> {
    match self {
        LoopState::Continue(y) => Ok(y),
        LoopState::Break(x) => Err(x),
    }
}
#[inline]
fn from_error(v: Self::Error) -> Self { LoopState::Break(v) }
#[inline]

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system · 2019-03-25T08:16:51.540Z

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