futures_util/future/
then.rs

1use futures_core::{Future, IntoFuture, Poll};
2use futures_core::task;
3use super::chain::Chain;
4
5/// Future for the `then` combinator, chaining computations on the end of
6/// another future regardless of its outcome.
7///
8/// This is created by the `Future::then` method.
9#[derive(Debug)]
10#[must_use = "futures do nothing unless polled"]
11pub struct Then<A, B, F> where A: Future, B: IntoFuture {
12    state: Chain<A, B::Future, F>,
13}
14
15pub fn new<A, B, F>(future: A, f: F) -> Then<A, B, F>
16    where A: Future,
17          B: IntoFuture,
18{
19    Then {
20        state: Chain::new(future, f),
21    }
22}
23
24impl<A, B, F> Future for Then<A, B, F>
25    where A: Future,
26          B: IntoFuture,
27          F: FnOnce(Result<A::Item, A::Error>) -> B,
28{
29    type Item = B::Item;
30    type Error = B::Error;
31
32    fn poll(&mut self, cx: &mut task::Context) -> Poll<B::Item, B::Error> {
33        self.state.poll(cx, |a, f| {
34            Ok(Err(f(a).into_future()))
35        })
36    }
37}
futures_util/future/then.rs

futures_util/future/
then.rs
