radicle-git/radicle-std-ext/src/ops.rs

// Copyright © 2021 The Radicle Link Contributors
//
// This file is part of radicle-link, distributed under the GPLv3 with Radicle
// Linking Exception. For full terms see the included LICENSE file.

//! Provides Try-trait for stable rust
//!
//! Probably doesn't work with `?`-desugaring. If the `nightly` feature is
//! enabled for this crate, the `std` version is enabled.

#[cfg(not(feature = "nightly"))]
pub use stable::{FromResidual, Try};
#[cfg(feature = "nightly")]
pub use std::ops::{FromResidual, Try};

mod stable {
    use std::{convert, ops::ControlFlow, task::Poll};

    pub trait Try: FromResidual {
        type Output;
        type Residual;

        fn from_output(output: Self::Output) -> Self;
        fn branch(self) -> ControlFlow<Self::Residual, Self::Output>;
    }

    pub trait FromResidual<R = <Self as Try>::Residual> {
        fn from_residual(residual: R) -> Self;
    }

    impl<B, C> Try for ControlFlow<B, C> {
        type Output = C;
        type Residual = ControlFlow<B, convert::Infallible>;

        #[inline]
        fn from_output(output: Self::Output) -> Self {
            ControlFlow::Continue(output)
        }

        #[inline]
        fn branch(self) -> ControlFlow<Self::Residual, Self::Output> {
            match self {
                ControlFlow::Continue(c) => ControlFlow::Continue(c),
                ControlFlow::Break(b) => ControlFlow::Break(ControlFlow::Break(b)),
            }
        }
    }

    impl<B, C> FromResidual for ControlFlow<B, C> {
        #[inline]
        fn from_residual(residual: ControlFlow<B, convert::Infallible>) -> Self {
            match residual {
                ControlFlow::Break(b) => ControlFlow::Break(b),
                _ => unreachable!(),
            }
        }
    }

    impl<T> Try for Option<T> {
        type Output = T;
        type Residual = Option<convert::Infallible>;

        #[inline]
        fn from_output(output: Self::Output) -> Self {
            Some(output)
        }

        #[inline]
        fn branch(self) -> ControlFlow<Self::Residual, Self::Output> {
            match self {
                Some(v) => ControlFlow::Continue(v),
                None => ControlFlow::Break(None),
            }
        }
    }

    impl<T> FromResidual for Option<T> {
        #[inline]
        fn from_residual(residual: Option<convert::Infallible>) -> Self {
            match residual {
                None => None,
                _ => unreachable!(),
            }
        }
    }

    impl<T, E> Try for Result<T, E> {
        type Output = T;
        type Residual = Result<convert::Infallible, E>;

        #[inline]
        fn from_output(output: Self::Output) -> Self {
            Ok(output)
        }

        #[inline]
        fn branch(self) -> ControlFlow<Self::Residual, Self::Output> {
            match self {
                Ok(v) => ControlFlow::Continue(v),
                Err(e) => ControlFlow::Break(Err(e)),
            }
        }
    }

    impl<T, E, F: From<E>> FromResidual<Result<convert::Infallible, E>> for Result<T, F> {
        #[inline]
        fn from_residual(residual: Result<convert::Infallible, E>) -> Self {
            match residual {
                Err(e) => Err(From::from(e)),
                _ => unreachable!(),
            }
        }
    }

    impl<T, E> Try for Poll<Option<Result<T, E>>> {
        type Output = Poll<Option<T>>;
        type Residual = Result<convert::Infallible, E>;

        #[inline]
        fn from_output(c: Self::Output) -> Self {
            c.map(|x| x.map(Ok))
        }

        #[inline]
        fn branch(self) -> ControlFlow<Self::Residual, Self::Output> {
            match self {
                Poll::Ready(Some(Ok(x))) => ControlFlow::Continue(Poll::Ready(Some(x))),
                Poll::Ready(Some(Err(e))) => ControlFlow::Break(Err(e)),
                Poll::Ready(None) => ControlFlow::Continue(Poll::Ready(None)),
                Poll::Pending => ControlFlow::Continue(Poll::Pending),
            }
        }
    }

    impl<T, E, F: From<E>> FromResidual<Result<convert::Infallible, E>> for Poll<Option<Result<T, F>>> {
        #[inline]
        fn from_residual(x: Result<convert::Infallible, E>) -> Self {
            match x {
                Err(e) => Poll::Ready(Some(Err(From::from(e)))),
                _ => unreachable!(),
            }
        }
    }

    impl<T, E> Try for Poll<Result<T, E>> {
        type Output = Poll<T>;
        type Residual = Result<convert::Infallible, E>;

        #[inline]
        fn from_output(c: Self::Output) -> Self {
            c.map(Ok)
        }

        #[inline]
        fn branch(self) -> ControlFlow<Self::Residual, Self::Output> {
            match self {
                Poll::Ready(Ok(x)) => ControlFlow::Continue(Poll::Ready(x)),
                Poll::Ready(Err(e)) => ControlFlow::Break(Err(e)),
                Poll::Pending => ControlFlow::Continue(Poll::Pending),
            }
        }
    }

    impl<T, E, F: From<E>> FromResidual<Result<convert::Infallible, E>> for Poll<Result<T, F>> {
        #[inline]
        fn from_residual(x: Result<convert::Infallible, E>) -> Self {
            match x {
                Err(e) => Poll::Ready(Err(From::from(e))),
                _ => unreachable!(),
            }
        }
    }
}