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use {Future, Poll, Async};
#[derive(Debug)]
#[must_use = "futures do nothing unless polled"]
pub struct Map<A, F> where A: Future {
future: A,
f: Option<F>,
}
pub fn new<A, F>(future: A, f: F) -> Map<A, F>
where A: Future,
{
Map {
future: future,
f: Some(f),
}
}
impl<U, A, F> Future for Map<A, F>
where A: Future,
F: FnOnce(A::Item) -> U,
{
type Item = U;
type Error = A::Error;
fn poll(&mut self) -> Poll<U, A::Error> {
let e = match self.future.poll() {
Ok(Async::NotReady) => return Ok(Async::NotReady),
Ok(Async::Ready(e)) => Ok(e),
Err(e) => Err(e),
};
e.map(self.f.take().expect("cannot poll Map twice"))
.map(Async::Ready)
}
}