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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);
}
}