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use {Async, Future, 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.
#[must_use = "streams do nothing unless polled"]
pub struct ForEach<S, F> {
    stream: S,
    f: F,
}

pub fn new<S, F>(s: S, f: F) -> ForEach<S, F>
    where S: Stream,
          F: FnMut(S::Item) -> Result<(), S::Error>,
{
    ForEach {
        stream: s,
        f: f,
    }
}

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

    fn poll(&mut self) -> Poll<(), S::Error> {
        loop {
            match try_ready!(self.stream.poll()) {
                Some(e) => try!((self.f)(e)),
                None => return Ok(Async::Ready(())),
            }
        }
    }
}