futures_util/future/
and_then.rs

1use futures_core::{Future, IntoFuture, Poll};
2use futures_core::task;
3
4use super::chain::Chain;
5
6/// Future for the `and_then` combinator, chaining a computation onto the end of
7/// another future which completes successfully.
8///
9/// This is created by the `Future::and_then` method.
10#[derive(Debug)]
11#[must_use = "futures do nothing unless polled"]
12pub struct AndThen<A, B, F> where A: Future, B: IntoFuture {
13    state: Chain<A, B::Future, F>,
14}
15
16pub fn new<A, B, F>(future: A, f: F) -> AndThen<A, B, F>
17    where A: Future,
18          B: IntoFuture,
19{
20    AndThen {
21        state: Chain::new(future, f),
22    }
23}
24
25impl<A, B, F> Future for AndThen<A, B, F>
26    where A: Future,
27          B: IntoFuture<Error=A::Error>,
28          F: FnOnce(A::Item) -> B,
29{
30    type Item = B::Item;
31    type Error = B::Error;
32
33    fn poll(&mut self, cx: &mut task::Context) -> Poll<B::Item, B::Error> {
34        self.state.poll(cx, |result, f| {
35            result.map(|e| {
36                Err(f(e).into_future())
37            })
38        })
39    }
40}
futures_util/future/and_then.rs

futures_util/future/
and_then.rs
