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    use {Async, Future, IntoFuture, Poll};
    use stream::Stream;

    /// A stream combinator which executes a unit closure over each item on a
    /// stream.
    ///
    /// This structure is returned by the `Stream::for_each` method.
    #[derive(Debug)]
    #[must_use = "streams do nothing unless polled"]
    pub struct ForEach<S, F, U> where U: IntoFuture {
        stream: S,
        f: F,
        fut: Option<U::Future>,
    }

    pub fn new<S, F, U>(s: S, f: F) -> ForEach<S, F, U>
        where S: Stream,
              F: FnMut(S::Item) -> U,
              U: IntoFuture<Item = (), Error = S::Error>,
    {
        ForEach {
            stream: s,
            f: f,
            fut: None,
        }
    }

    impl<S, F, U> Future for ForEach<S, F, U>
        where S: Stream,
              F: FnMut(S::Item) -> U,
              U: IntoFuture<Item= (), Error = S::Error>,
    {
        type Item = ();
        type Error = S::Error;

        fn poll(&mut self) -> Poll<(), S::Error> {
            loop {
                if let Some(mut fut) = self.fut.take() {
                    if fut.poll()?.is_not_ready() {
                        self.fut = Some(fut);
                        return Ok(Async::NotReady);
                    }
                }

                match try_ready!(self.stream.poll()) {
                    Some(e) => self.fut = Some((self.f)(e).into_future()),
                    None => return Ok(Async::Ready(())),
                }
            }
        }
    }

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