blob: b77be1575c8393de2e65d00ab334a3766d68de70 [file] [log] [blame]
use core::marker::Unpin;
use core::pin::PinMut;
use futures_core::future::Future;
use futures_core::task::{self, Poll};
use pin_utils::{unsafe_pinned, unsafe_unpinned};
/// Future for the `map` combinator, changing the type of a future.
///
/// This is created by the `Future::map` method.
#[derive(Debug)]
#[must_use = "futures do nothing unless polled"]
pub struct Map<Fut, F> {
future: Fut,
f: Option<F>,
}
impl<Fut, F> Map<Fut, F> {
unsafe_pinned!(future: Fut);
unsafe_unpinned!(f: Option<F>);
/// Creates a new Map.
pub(super) fn new(future: Fut, f: F) -> Map<Fut, F> {
Map { future, f: Some(f) }
}
}
impl<Fut: Unpin, F> Unpin for Map<Fut, F> {}
impl<Fut, F, T> Future for Map<Fut, F>
where Fut: Future,
F: FnOnce(Fut::Output) -> T,
{
type Output = T;
fn poll(mut self: PinMut<Self>, cx: &mut task::Context) -> Poll<T> {
match self.future().poll(cx) {
Poll::Pending => Poll::Pending,
Poll::Ready(output) => {
let f = self.f().take()
.expect("Map must not be polled after it returned `Poll::Ready`");
Poll::Ready(f(output))
}
}
}
}