#
actix_utils/future/
either.rs

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    //! A symmetric either future.

    use core::{
        future::Future,
        pin::Pin,
        task::{Context, Poll},
    };

    use pin_project_lite::pin_project;

    pin_project! {
        /// Combines two different futures that have the same output type.
        ///
        /// Construct variants with [`Either::left`] and [`Either::right`].
        ///
        /// # Examples
        /// ```
        /// use actix_utils::future::{ready, Ready, Either};
        ///
        /// # async fn run() {
        /// let res = Either::<_, Ready<usize>>::left(ready(42));
        /// assert_eq!(res.await, 42);
        ///
        /// let res = Either::<Ready<usize>, _>::right(ready(43));
        /// assert_eq!(res.await, 43);
        /// # }
        /// ```
        #[project = EitherProj]
        #[derive(Debug, Clone)]
        pub enum Either<L, R> {
            /// A value of type `L`.
            #[allow(missing_docs)]
            Left { #[pin] value: L },

            /// A value of type `R`.
            #[allow(missing_docs)]
            Right { #[pin] value: R },
        }
    }

    impl<L, R> Either<L, R> {
        /// Creates new `Either` using left variant.
        #[inline]
        pub fn left(value: L) -> Either<L, R> {
            Either::Left { value }
        }

        /// Creates new `Either` using right variant.
        #[inline]
        pub fn right(value: R) -> Either<L, R> {
            Either::Right { value }
        }
    }

    impl<T> Either<T, T> {
        /// Unwraps into inner value when left and right have a common type.
        #[inline]
        pub fn into_inner(self) -> T {
            match self {
                Either::Left { value } => value,
                Either::Right { value } => value,
            }
        }
    }

    impl<L, R> Future for Either<L, R>
    where
        L: Future,
        R: Future<Output = L::Output>,
    {
        type Output = L::Output;

        #[inline]
        fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
            match self.project() {
                EitherProj::Left { value } => value.poll(cx),
                EitherProj::Right { value } => value.poll(cx),
            }
        }
    }

    #[cfg(test)]
    mod tests {
        use super::*;
        use crate::future::{ready, Ready};

        #[actix_rt::test]
        async fn test_either() {
            let res = Either::<_, Ready<usize>>::left(ready(42));
            assert_eq!(res.await, 42);

            let res = Either::<Ready<usize>, _>::right(ready(43));
            assert_eq!(res.await, 43);
        }
    }