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    //! Asynchronous streams
    //!
    //! This module contains the `Stream` trait and a number of adaptors for this
    //! trait. This trait is very similar to the `Iterator` trait in the standard
    //! library except that it expresses the concept of blocking as well. A stream
    //! here is a sequential sequence of values which may take some amount of time
    //! in between to produce.
    //!
    //! A stream may request that it is blocked between values while the next value
    //! is calculated, and provides a way to get notified once the next value is
    //! ready as well.
    //!
    //! You can find more information/tutorials about streams [online at
    //! https://tokio.rs][online]
    //!
    //! [online]: https://tokio.rs/docs/getting-started/streams-and-sinks/

    use {IntoFuture, Poll};

    mod iter;
    #[allow(deprecated)]
    pub use self::iter::{iter, Iter};
    #[cfg(feature = "with-deprecated")]
    #[allow(deprecated)]
    pub use self::Iter as IterStream;
    mod iter_ok;
    pub use self::iter_ok::{iter_ok, IterOk};
    mod iter_result;
    pub use self::iter_result::{iter_result, IterResult};

    mod repeat;
    pub use self::repeat::{repeat, Repeat};

    mod and_then;
    mod chain;
    mod concat;
    mod empty;
    mod filter;
    mod filter_map;
    mod flatten;
    mod fold;
    mod for_each;
    mod from_err;
    mod fuse;
    mod future;
    mod inspect;
    mod inspect_err;
    mod map;
    mod map_err;
    mod merge;
    mod once;
    mod or_else;
    mod peek;
    mod poll_fn;
    mod select;
    mod skip;
    mod skip_while;
    mod take;
    mod take_while;
    mod then;
    mod unfold;
    mod zip;
    mod forward;
    pub use self::and_then::AndThen;
    pub use self::chain::Chain;
    #[allow(deprecated)]
    pub use self::concat::Concat;
    pub use self::concat::Concat2;
    pub use self::empty::{Empty, empty};
    pub use self::filter::Filter;
    pub use self::filter_map::FilterMap;
    pub use self::flatten::Flatten;
    pub use self::fold::Fold;
    pub use self::for_each::ForEach;
    pub use self::from_err::FromErr;
    pub use self::fuse::Fuse;
    pub use self::future::StreamFuture;
    pub use self::inspect::Inspect;
    pub use self::inspect_err::InspectErr;
    pub use self::map::Map;
    pub use self::map_err::MapErr;
    #[allow(deprecated)]
    pub use self::merge::{Merge, MergedItem};
    pub use self::once::{Once, once};
    pub use self::or_else::OrElse;
    pub use self::peek::Peekable;
    pub use self::poll_fn::{poll_fn, PollFn};
    pub use self::select::Select;
    pub use self::skip::Skip;
    pub use self::skip_while::SkipWhile;
    pub use self::take::Take;
    pub use self::take_while::TakeWhile;
    pub use self::then::Then;
    pub use self::unfold::{Unfold, unfold};
    pub use self::zip::Zip;
    pub use self::forward::Forward;
    use sink::{Sink};

    if_std! {
        use std;

        mod buffered;
        mod buffer_unordered;
        mod catch_unwind;
        mod chunks;
        mod collect;
        mod wait;
        mod channel;
        mod split;
        pub mod futures_unordered;
        mod futures_ordered;
        pub use self::buffered::Buffered;
        pub use self::buffer_unordered::BufferUnordered;
        pub use self::catch_unwind::CatchUnwind;
        pub use self::chunks::Chunks;
        pub use self::collect::Collect;
        pub use self::wait::Wait;
        pub use self::split::{SplitStream, SplitSink, ReuniteError};
        pub use self::futures_unordered::FuturesUnordered;
        pub use self::futures_ordered::{futures_ordered, FuturesOrdered};

        #[doc(hidden)]
        #[cfg(feature = "with-deprecated")]
        #[allow(deprecated)]
        pub use self::channel::{channel, Sender, Receiver, FutureSender, SendError};

        /// A type alias for `Box<Stream + Send>`
        #[doc(hidden)]
        #[deprecated(note = "removed without replacement, recommended to use a \
                             local extension trait or function if needed, more \
                             details in https://github.com/rust-lang-nursery/futures-rs/issues/228")]
        pub type BoxStream<T, E> = ::std::boxed::Box<Stream<Item = T, Error = E> + Send>;

        impl<S: ?Sized + Stream> Stream for ::std::boxed::Box<S> {
            type Item = S::Item;
            type Error = S::Error;

            fn poll(&mut self) -> Poll<Option<Self::Item>, Self::Error> {
                (**self).poll()
            }
        }
    }

    /// A stream of values, not all of which may have been produced yet.
    ///
    /// `Stream` is a trait to represent any source of sequential events or items
    /// which acts like an iterator but long periods of time may pass between
    /// items. Like `Future` the methods of `Stream` never block and it is thus
    /// suitable for programming in an asynchronous fashion. This trait is very
    /// similar to the `Iterator` trait in the standard library where `Some` is
    /// used to signal elements of the stream and `None` is used to indicate that
    /// the stream is finished.
    ///
    /// Like futures a stream has basic combinators to transform the stream, perform
    /// more work on each item, etc.
    ///
    /// You can find more information/tutorials about streams [online at
    /// https://tokio.rs][online]
    ///
    /// [online]: https://tokio.rs/docs/getting-started/streams-and-sinks/
    ///
    /// # Streams as Futures
    ///
    /// Any instance of `Stream` can also be viewed as a `Future` where the resolved
    /// value is the next item in the stream along with the rest of the stream. The
    /// `into_future` adaptor can be used here to convert any stream into a future
    /// for use with other future methods like `join` and `select`.
    ///
    /// # Errors
    ///
    /// Streams, like futures, can also model errors in their computation. All
    /// streams have an associated `Error` type like with futures. Currently as of
    /// the 0.1 release of this library an error on a stream **does not terminate
    /// the stream**. That is, after one error is received, another error may be
    /// received from the same stream (it's valid to keep polling).
    ///
    /// This property of streams, however, is [being considered] for change in 0.2
    /// where an error on a stream is similar to `None`, it terminates the stream
    /// entirely. If one of these use cases suits you perfectly and not the other,
    /// please feel welcome to comment on [the issue][being considered]!
    ///
    /// [being considered]: https://github.com/rust-lang-nursery/futures-rs/issues/206
    pub trait Stream {
        /// The type of item this stream will yield on success.
        type Item;

        /// The type of error this stream may generate.
        type Error;

        /// Attempt to pull out the next value of this stream, returning `None` if
        /// the stream is finished.
        ///
        /// This method, like `Future::poll`, is the sole method of pulling out a
        /// value from a stream. This method must also be run within the context of
        /// a task typically and implementors of this trait must ensure that
        /// implementations of this method do not block, as it may cause consumers
        /// to behave badly.
        ///
        /// # Return value
        ///
        /// If `NotReady` is returned then this stream's next value is not ready
        /// yet and implementations will ensure that the current task will be
        /// notified when the next value may be ready. If `Some` is returned then
        /// the returned value represents the next value on the stream. `Err`
        /// indicates an error happened, while `Ok` indicates whether there was a
        /// new item on the stream or whether the stream has terminated.
        ///
        /// # Panics
        ///
        /// Once a stream is finished, that is `Ready(None)` has been returned,
        /// further calls to `poll` may result in a panic or other "bad behavior".
        /// If this is difficult to guard against then the `fuse` adapter can be
        /// used to ensure that `poll` always has well-defined semantics.
        // TODO: more here
        fn poll(&mut self) -> Poll<Option<Self::Item>, Self::Error>;

        // TODO: should there also be a method like `poll` but doesn't return an
        //       item? basically just says "please make more progress internally"
        //       seems crucial for buffering to actually make any sense.

        /// Creates an iterator which blocks the current thread until each item of
        /// this stream is resolved.
        ///
        /// This method will consume ownership of this stream, returning an
        /// implementation of a standard iterator. This iterator will *block the
        /// current thread* on each call to `next` if the item in the stream isn't
        /// ready yet.
        ///
        /// > **Note:** This method is not appropriate to call on event loops or
        /// >           similar I/O situations because it will prevent the event
        /// >           loop from making progress (this blocks the thread). This
        /// >           method should only be called when it's guaranteed that the
        /// >           blocking work associated with this stream will be completed
        /// >           by another thread.
        ///
        /// This method is only available when the `use_std` feature of this
        /// library is activated, and it is activated by default.
        ///
        /// # Panics
        ///
        /// The returned iterator does not attempt to catch panics. If the `poll`
        /// function panics, panics will be propagated to the caller of `next`.
        #[cfg(feature = "use_std")]
        fn wait(self) -> Wait<Self>
            where Self: Sized
        {
            wait::new(self)
        }

        /// Convenience function for turning this stream into a trait object.
        ///
        /// This simply avoids the need to write `Box::new` and can often help with
        /// type inference as well by always returning a trait object. Note that
        /// this method requires the `Send` bound and returns a `BoxStream`, which
        /// also encodes this. If you'd like to create a `Box<Stream>` without the
        /// `Send` bound, then the `Box::new` function can be used instead.
        ///
        /// This method is only available when the `use_std` feature of this
        /// library is activated, and it is activated by default.
        ///
        /// # Examples
        ///
        /// ```
        /// use futures::stream::*;
        /// use futures::sync::mpsc;
        ///
        /// let (_tx, rx) = mpsc::channel(1);
        /// let a: BoxStream<i32, ()> = rx.boxed();
        /// ```
        #[cfg(feature = "use_std")]
        #[doc(hidden)]
        #[deprecated(note = "removed without replacement, recommended to use a \
                             local extension trait or function if needed, more \
                             details in https://github.com/rust-lang-nursery/futures-rs/issues/228")]
        #[allow(deprecated)]
        fn boxed(self) -> BoxStream<Self::Item, Self::Error>
            where Self: Sized + Send + 'static,
        {
            ::std::boxed::Box::new(self)
        }

        /// Converts this stream into a `Future`.
        ///
        /// A stream can be viewed as a future which will resolve to a pair containing
        /// the next element of the stream plus the remaining stream. If the stream
        /// terminates, then the next element is `None` and the remaining stream is
        /// still passed back, to allow reclamation of its resources.
        ///
        /// The returned future can be used to compose streams and futures together by
        /// placing everything into the "world of futures".
        fn into_future(self) -> StreamFuture<Self>
            where Self: Sized
        {
            future::new(self)
        }

        /// Converts a stream of type `T` to a stream of type `U`.
        ///
        /// The provided closure is executed over all elements of this stream as
        /// they are made available, and the callback will be executed inline with
        /// calls to `poll`.
        ///
        /// Note that this function consumes the receiving stream and returns a
        /// wrapped version of it, similar to the existing `map` methods in the
        /// standard library.
        ///
        /// # Examples
        ///
        /// ```
        /// use futures::prelude::*;
        /// use futures::sync::mpsc;
        ///
        /// let (_tx, rx) = mpsc::channel::<i32>(1);
        /// let rx = rx.map(|x| x + 3);
        /// ```
        fn map<U, F>(self, f: F) -> Map<Self, F>
            where F: FnMut(Self::Item) -> U,
                  Self: Sized
        {
            map::new(self, f)
        }

        /// Converts a stream of error type `T` to a stream of error type `U`.
        ///
        /// The provided closure is executed over all errors of this stream as
        /// they are made available, and the callback will be executed inline with
        /// calls to `poll`.
        ///
        /// Note that this function consumes the receiving stream and returns a
        /// wrapped version of it, similar to the existing `map_err` methods in the
        /// standard library.
        ///
        /// # Examples
        ///
        /// ```
        /// use futures::prelude::*;
        /// use futures::sync::mpsc;
        ///
        /// let (_tx, rx) = mpsc::channel::<i32>(1);
        /// let rx = rx.map_err(|()| 3);
        /// ```
        fn map_err<U, F>(self, f: F) -> MapErr<Self, F>
            where F: FnMut(Self::Error) -> U,
                  Self: Sized
        {
            map_err::new(self, f)
        }

        /// Filters the values produced by this stream according to the provided
        /// predicate.
        ///
        /// As values of this stream are made available, the provided predicate will
        /// be run against them. If the predicate returns `true` then the stream
        /// will yield the value, but if the predicate returns `false` then the
        /// value will be discarded and the next value will be produced.
        ///
        /// All errors are passed through without filtering in this combinator.
        ///
        /// Note that this function consumes the receiving stream and returns a
        /// wrapped version of it, similar to the existing `filter` methods in the
        /// standard library.
        ///
        /// # Examples
        ///
        /// ```
        /// use futures::prelude::*;
        /// use futures::sync::mpsc;
        ///
        /// let (_tx, rx) = mpsc::channel::<i32>(1);
        /// let evens = rx.filter(|x| x % 2 == 0);
        /// ```
        fn filter<F>(self, f: F) -> Filter<Self, F>
            where F: FnMut(&Self::Item) -> bool,
                  Self: Sized
        {
            filter::new(self, f)
        }

        /// Filters the values produced by this stream while simultaneously mapping
        /// them to a different type.
        ///
        /// As values of this stream are made available, the provided function will
        /// be run on them. If the predicate returns `Some(e)` then the stream will
        /// yield the value `e`, but if the predicate returns `None` then the next
        /// value will be produced.
        ///
        /// All errors are passed through without filtering in this combinator.
        ///
        /// Note that this function consumes the receiving stream and returns a
        /// wrapped version of it, similar to the existing `filter_map` methods in the
        /// standard library.
        ///
        /// # Examples
        ///
        /// ```
        /// use futures::prelude::*;
        /// use futures::sync::mpsc;
        ///
        /// let (_tx, rx) = mpsc::channel::<i32>(1);
        /// let evens_plus_one = rx.filter_map(|x| {
        ///     if x % 0 == 2 {
        ///         Some(x + 1)
        ///     } else {
        ///         None
        ///     }
        /// });
        /// ```
        fn filter_map<F, B>(self, f: F) -> FilterMap<Self, F>
            where F: FnMut(Self::Item) -> Option<B>,
                  Self: Sized
        {
            filter_map::new(self, f)
        }

        /// Chain on a computation for when a value is ready, passing the resulting
        /// item to the provided closure `f`.
        ///
        /// This function can be used to ensure a computation runs regardless of
        /// the next value on the stream. The closure provided will be yielded a
        /// `Result` once a value is ready, and the returned future will then be run
        /// to completion to produce the next value on this stream.
        ///
        /// The returned value of the closure must implement the `IntoFuture` trait
        /// and can represent some more work to be done before the composed stream
        /// is finished. Note that the `Result` type implements the `IntoFuture`
        /// trait so it is possible to simply alter the `Result` yielded to the
        /// closure and return it.
        ///
        /// Note that this function consumes the receiving stream and returns a
        /// wrapped version of it.
        ///
        /// # Examples
        ///
        /// ```
        /// use futures::prelude::*;
        /// use futures::sync::mpsc;
        ///
        /// let (_tx, rx) = mpsc::channel::<i32>(1);
        ///
        /// let rx = rx.then(|result| {
        ///     match result {
        ///         Ok(e) => Ok(e + 3),
        ///         Err(()) => Err(4),
        ///     }
        /// });
        /// ```
        fn then<F, U>(self, f: F) -> Then<Self, F, U>
            where F: FnMut(Result<Self::Item, Self::Error>) -> U,
                  U: IntoFuture,
                  Self: Sized
        {
            then::new(self, f)
        }

        /// Chain on a computation for when a value is ready, passing the successful
        /// results to the provided closure `f`.
        ///
        /// This function can be used to run a unit of work when the next successful
        /// value on a stream is ready. The closure provided will be yielded a value
        /// when ready, and the returned future will then be run to completion to
        /// produce the next value on this stream.
        ///
        /// Any errors produced by this stream will not be passed to the closure,
        /// and will be passed through.
        ///
        /// The returned value of the closure must implement the `IntoFuture` trait
        /// and can represent some more work to be done before the composed stream
        /// is finished. Note that the `Result` type implements the `IntoFuture`
        /// trait so it is possible to simply alter the `Result` yielded to the
        /// closure and return it.
        ///
        /// Note that this function consumes the receiving stream and returns a
        /// wrapped version of it.
        ///
        /// To process the entire stream and return a single future representing
        /// success or error, use `for_each` instead.
        ///
        /// # Examples
        ///
        /// ```
        /// use futures::prelude::*;
        /// use futures::sync::mpsc;
        ///
        /// let (_tx, rx) = mpsc::channel::<i32>(1);
        ///
        /// let rx = rx.and_then(|result| {
        ///     if result % 2 == 0 {
        ///         Ok(result)
        ///     } else {
        ///         Err(())
        ///     }
        /// });
        /// ```
        fn and_then<F, U>(self, f: F) -> AndThen<Self, F, U>
            where F: FnMut(Self::Item) -> U,
                  U: IntoFuture<Error = Self::Error>,
                  Self: Sized
        {
            and_then::new(self, f)
        }

        /// Chain on a computation for when an error happens, passing the
        /// erroneous result to the provided closure `f`.
        ///
        /// This function can be used to run a unit of work and attempt to recover from
        /// an error if one happens. The closure provided will be yielded an error
        /// when one appears, and the returned future will then be run to completion
        /// to produce the next value on this stream.
        ///
        /// Any successful values produced by this stream will not be passed to the
        /// closure, and will be passed through.
        ///
        /// The returned value of the closure must implement the `IntoFuture` trait
        /// and can represent some more work to be done before the composed stream
        /// is finished. Note that the `Result` type implements the `IntoFuture`
        /// trait so it is possible to simply alter the `Result` yielded to the
        /// closure and return it.
        ///
        /// Note that this function consumes the receiving stream and returns a
        /// wrapped version of it.
        fn or_else<F, U>(self, f: F) -> OrElse<Self, F, U>
            where F: FnMut(Self::Error) -> U,
                  U: IntoFuture<Item = Self::Item>,
                  Self: Sized
        {
            or_else::new(self, f)
        }

        /// Collect all of the values of this stream into a vector, returning a
        /// future representing the result of that computation.
        ///
        /// This combinator will collect all successful results of this stream and
        /// collect them into a `Vec<Self::Item>`. If an error happens then all
        /// collected elements will be dropped and the error will be returned.
        ///
        /// The returned future will be resolved whenever an error happens or when
        /// the stream returns `Ok(None)`.
        ///
        /// This method is only available when the `use_std` feature of this
        /// library is activated, and it is activated by default.
        ///
        /// # Examples
        ///
        /// ```
        /// use std::thread;
        ///
        /// use futures::prelude::*;
        /// use futures::sync::mpsc;
        ///
        /// let (mut tx, rx) = mpsc::channel(1);
        ///
        /// thread::spawn(|| {
        ///     for i in (0..5).rev() {
        ///         tx = tx.send(i + 1).wait().unwrap();
        ///     }
        /// });
        ///
        /// let mut result = rx.collect();
        /// assert_eq!(result.wait(), Ok(vec![5, 4, 3, 2, 1]));
        /// ```
        #[cfg(feature = "use_std")]
        fn collect(self) -> Collect<Self>
            where Self: Sized
        {
            collect::new(self)
        }

        /// Concatenate all results of a stream into a single extendable
        /// destination, returning a future representing the end result.
        ///
        /// This combinator will extend the first item with the contents
        /// of all the successful results of the stream. If the stream is
        /// empty, the default value will be returned. If an error occurs,
        /// all the results will be dropped and the error will be returned.
        ///
        /// The name `concat2` is an intermediate measure until the release of
        /// futures 0.2, at which point it will be renamed back to `concat`.
        ///
        /// # Examples
        ///
        /// ```
        /// use std::thread;
        ///
        /// use futures::prelude::*;
        /// use futures::sync::mpsc;
        ///
        /// let (mut tx, rx) = mpsc::channel(1);
        ///
        /// thread::spawn(move || {
        ///     for i in (0..3).rev() {
        ///         let n = i * 3;
        ///         tx = tx.send(vec![n + 1, n + 2, n + 3]).wait().unwrap();
        ///     }
        /// });
        /// let result = rx.concat2();
        /// assert_eq!(result.wait(), Ok(vec![7, 8, 9, 4, 5, 6, 1, 2, 3]));
        /// ```
        fn concat2(self) -> Concat2<Self>
            where Self: Sized,
                  Self::Item: Extend<<<Self as Stream>::Item as IntoIterator>::Item> + IntoIterator + Default,
        {
            concat::new2(self)
        }

        /// Concatenate all results of a stream into a single extendable
        /// destination, returning a future representing the end result.
        ///
        /// This combinator will extend the first item with the contents
        /// of all the successful results of the stream. If an error occurs,
        /// all the results will be dropped and the error will be returned.
        ///
        /// # Examples
        ///
        /// ```
        /// use std::thread;
        ///
        /// use futures::prelude::*;
        /// use futures::sync::mpsc;
        ///
        /// let (mut tx, rx) = mpsc::channel(1);
        ///
        /// thread::spawn(move || {
        ///     for i in (0..3).rev() {
        ///         let n = i * 3;
        ///         tx = tx.send(vec![n + 1, n + 2, n + 3]).wait().unwrap();
        ///     }
        /// });
        /// let result = rx.concat();
        /// assert_eq!(result.wait(), Ok(vec![7, 8, 9, 4, 5, 6, 1, 2, 3]));
        /// ```
        ///
        /// # Panics
        ///
        /// It's important to note that this function will panic if the stream
        /// is empty, which is the reason for its deprecation.
        #[deprecated(since="0.1.14", note="please use `Stream::concat2` instead")]
        #[allow(deprecated)]
        fn concat(self) -> Concat<Self>
            where Self: Sized,
                  Self::Item: Extend<<<Self as Stream>::Item as IntoIterator>::Item> + IntoIterator,
        {
            concat::new(self)
        }

        /// Execute an accumulating computation over a stream, collecting all the
        /// values into one final result.
        ///
        /// This combinator will collect all successful results of this stream
        /// according to the closure provided. The initial state is also provided to
        /// this method and then is returned again by each execution of the closure.
        /// Once the entire stream has been exhausted the returned future will
        /// resolve to this value.
        ///
        /// If an error happens then collected state will be dropped and the error
        /// will be returned.
        ///
        /// # Examples
        ///
        /// ```
        /// use futures::prelude::*;
        /// use futures::stream;
        /// use futures::future;
        ///
        /// let number_stream = stream::iter_ok::<_, ()>(0..6);
        /// let sum = number_stream.fold(0, |acc, x| future::ok(acc + x));
        /// assert_eq!(sum.wait(), Ok(15));
        /// ```
        fn fold<F, T, Fut>(self, init: T, f: F) -> Fold<Self, F, Fut, T>
            where F: FnMut(T, Self::Item) -> Fut,
                  Fut: IntoFuture<Item = T>,
                  Self::Error: From<Fut::Error>,
                  Self: Sized
        {
            fold::new(self, f, init)
        }

        /// Flattens a stream of streams into just one continuous stream.
        ///
        /// If this stream's elements are themselves streams then this combinator
        /// will flatten out the entire stream to one long chain of elements. Any
        /// errors are passed through without looking at them, but otherwise each
        /// individual stream will get exhausted before moving on to the next.
        ///
        /// ```
        /// use std::thread;
        ///
        /// use futures::prelude::*;
        /// use futures::sync::mpsc;
        ///
        /// let (tx1, rx1) = mpsc::channel::<i32>(1);
        /// let (tx2, rx2) = mpsc::channel::<i32>(1);
        /// let (tx3, rx3) = mpsc::channel(1);
        ///
        /// thread::spawn(|| {
        ///     tx1.send(1).wait().unwrap()
        ///        .send(2).wait().unwrap();
        /// });
        /// thread::spawn(|| {
        ///     tx2.send(3).wait().unwrap()
        ///        .send(4).wait().unwrap();
        /// });
        /// thread::spawn(|| {
        ///     tx3.send(rx1).wait().unwrap()
        ///        .send(rx2).wait().unwrap();
        /// });
        ///
        /// let mut result = rx3.flatten().collect();
        /// assert_eq!(result.wait(), Ok(vec![1, 2, 3, 4]));
        /// ```
        fn flatten(self) -> Flatten<Self>
            where Self::Item: Stream,
                  <Self::Item as Stream>::Error: From<Self::Error>,
                  Self: Sized
        {
            flatten::new(self)
        }

        /// Skip elements on this stream while the predicate provided resolves to
        /// `true`.
        ///
        /// This function, like `Iterator::skip_while`, will skip elements on the
        /// stream until the `predicate` resolves to `false`. Once one element
        /// returns false all future elements will be returned from the underlying
        /// stream.
        fn skip_while<P, R>(self, pred: P) -> SkipWhile<Self, P, R>
            where P: FnMut(&Self::Item) -> R,
                  R: IntoFuture<Item=bool, Error=Self::Error>,
                  Self: Sized
        {
            skip_while::new(self, pred)
        }

        /// Take elements from this stream while the predicate provided resolves to
        /// `true`.
        ///
        /// This function, like `Iterator::take_while`, will take elements from the
        /// stream until the `predicate` resolves to `false`. Once one element
        /// returns false it will always return that the stream is done.
        fn take_while<P, R>(self, pred: P) -> TakeWhile<Self, P, R>
            where P: FnMut(&Self::Item) -> R,
                  R: IntoFuture<Item=bool, Error=Self::Error>,
                  Self: Sized
        {
            take_while::new(self, pred)
        }

        /// Runs this stream to completion, executing the provided closure for each
        /// element on the stream.
        ///
        /// The closure provided will be called for each item this stream resolves
        /// to successfully, producing a future. That future will then be executed
        /// to completion before moving on to the next item.
        ///
        /// The returned value is a `Future` where the `Item` type is `()` and
        /// errors are otherwise threaded through. Any error on the stream or in the
        /// closure will cause iteration to be halted immediately and the future
        /// will resolve to that error.
        ///
        /// To process each item in the stream and produce another stream instead
        /// of a single future, use `and_then` instead.
        fn for_each<F, U>(self, f: F) -> ForEach<Self, F, U>
            where F: FnMut(Self::Item) -> U,
                  U: IntoFuture<Item=(), Error = Self::Error>,
                  Self: Sized
        {
            for_each::new(self, f)
        }

        /// Map this stream's error to any error implementing `From` for
        /// this stream's `Error`, returning a new stream.
        ///
        /// This function does for streams what `try!` does for `Result`,
        /// by letting the compiler infer the type of the resulting error.
        /// Just as `map_err` above, this is useful for example to ensure
        /// that streams have the same error type when used with
        /// combinators.
        ///
        /// Note that this function consumes the receiving stream and returns a
        /// wrapped version of it.
        fn from_err<E: From<Self::Error>>(self) -> FromErr<Self, E>
            where Self: Sized,
        {
            from_err::new(self)
        }

        /// Creates a new stream of at most `amt` items of the underlying stream.
        ///
        /// Once `amt` items have been yielded from this stream then it will always
        /// return that the stream is done.
        ///
        /// # Errors
        ///
        /// Any errors yielded from underlying stream, before the desired amount of
        /// items is reached, are passed through and do not affect the total number
        /// of items taken.
        fn take(self, amt: u64) -> Take<Self>
            where Self: Sized
        {
            take::new(self, amt)
        }

        /// Creates a new stream which skips `amt` items of the underlying stream.
        ///
        /// Once `amt` items have been skipped from this stream then it will always
        /// return the remaining items on this stream.
        ///
        /// # Errors
        ///
        /// All errors yielded from underlying stream are passed through and do not
        /// affect the total number of items skipped.
        fn skip(self, amt: u64) -> Skip<Self>
            where Self: Sized
        {
            skip::new(self, amt)
        }

        /// Fuse a stream such that `poll` will never again be called once it has
        /// finished.
        ///
        /// Currently once a stream has returned `None` from `poll` any further
        /// calls could exhibit bad behavior such as block forever, panic, never
        /// return, etc. If it is known that `poll` may be called after stream has
        /// already finished, then this method can be used to ensure that it has
        /// defined semantics.
        ///
        /// Once a stream has been `fuse`d and it finishes, then it will forever
        /// return `None` from `poll`. This, unlike for the traits `poll` method,
        /// is guaranteed.
        ///
        /// Also note that as soon as this stream returns `None` it will be dropped
        /// to reclaim resources associated with it.
        fn fuse(self) -> Fuse<Self>
            where Self: Sized
        {
            fuse::new(self)
        }

        /// Borrows a stream, rather than consuming it.
        ///
        /// This is useful to allow applying stream adaptors while still retaining
        /// ownership of the original stream.
        ///
        /// ```
        /// use futures::prelude::*;
        /// use futures::stream;
        /// use futures::future;
        ///
        /// let mut stream = stream::iter_ok::<_, ()>(1..5);
        ///
        /// let sum = stream.by_ref().take(2).fold(0, |a, b| future::ok(a + b)).wait();
        /// assert_eq!(sum, Ok(3));
        ///
        /// // You can use the stream again
        /// let sum = stream.take(2).fold(0, |a, b| future::ok(a + b)).wait();
        /// assert_eq!(sum, Ok(7));
        /// ```
        fn by_ref(&mut self) -> &mut Self
            where Self: Sized
        {
            self
        }

        /// Catches unwinding panics while polling the stream.
        ///
        /// Caught panic (if any) will be the last element of the resulting stream.
        ///
        /// In general, panics within a stream can propagate all the way out to the
        /// task level. This combinator makes it possible to halt unwinding within
        /// the stream itself. It's most commonly used within task executors. This
        /// method should not be used for error handling.
        ///
        /// Note that this method requires the `UnwindSafe` bound from the standard
        /// library. This isn't always applied automatically, and the standard
        /// library provides an `AssertUnwindSafe` wrapper type to apply it
        /// after-the fact. To assist using this method, the `Stream` trait is also
        /// implemented for `AssertUnwindSafe<S>` where `S` implements `Stream`.
        ///
        /// This method is only available when the `use_std` feature of this
        /// library is activated, and it is activated by default.
        ///
        /// # Examples
        ///
        /// ```rust
        /// use futures::prelude::*;
        /// use futures::stream;
        ///
        /// let stream = stream::iter_ok::<_, bool>(vec![Some(10), None, Some(11)]);
        /// // panic on second element
        /// let stream_panicking = stream.map(|o| o.unwrap());
        /// let mut iter = stream_panicking.catch_unwind().wait();
        ///
        /// assert_eq!(Ok(10), iter.next().unwrap().ok().unwrap());
        /// assert!(iter.next().unwrap().is_err());
        /// assert!(iter.next().is_none());
        /// ```
        #[cfg(feature = "use_std")]
        fn catch_unwind(self) -> CatchUnwind<Self>
            where Self: Sized + std::panic::UnwindSafe
        {
            catch_unwind::new(self)
        }

        /// An adaptor for creating a buffered list of pending futures.
        ///
        /// If this stream's item can be converted into a future, then this adaptor
        /// will buffer up to at most `amt` futures and then return results in the
        /// same order as the underlying stream. No more than `amt` futures will be
        /// buffered at any point in time, and less than `amt` may also be buffered
        /// depending on the state of each future.
        ///
        /// The returned stream will be a stream of each future's result, with
        /// errors passed through whenever they occur.
        ///
        /// This method is only available when the `use_std` feature of this
        /// library is activated, and it is activated by default.
        #[cfg(feature = "use_std")]
        fn buffered(self, amt: usize) -> Buffered<Self>
            where Self::Item: IntoFuture<Error = <Self as Stream>::Error>,
                  Self: Sized
        {
            buffered::new(self, amt)
        }

        /// An adaptor for creating a buffered list of pending futures (unordered).
        ///
        /// If this stream's item can be converted into a future, then this adaptor
        /// will buffer up to `amt` futures and then return results in the order
        /// in which they complete. No more than `amt` futures will be buffered at
        /// any point in time, and less than `amt` may also be buffered depending on
        /// the state of each future.
        ///
        /// The returned stream will be a stream of each future's result, with
        /// errors passed through whenever they occur.
        ///
        /// This method is only available when the `use_std` feature of this
        /// library is activated, and it is activated by default.
        #[cfg(feature = "use_std")]
        fn buffer_unordered(self, amt: usize) -> BufferUnordered<Self>
            where Self::Item: IntoFuture<Error = <Self as Stream>::Error>,
                  Self: Sized
        {
            buffer_unordered::new(self, amt)
        }

        /// An adapter for merging the output of two streams.
        ///
        /// The merged stream produces items from one or both of the underlying
        /// streams as they become available. Errors, however, are not merged: you
        /// get at most one error at a time.
        #[deprecated(note = "functionality provided by `select` now")]
        #[allow(deprecated)]
        fn merge<S>(self, other: S) -> Merge<Self, S>
            where S: Stream<Error = Self::Error>,
                  Self: Sized,
        {
            merge::new(self, other)
        }

        /// An adapter for zipping two streams together.
        ///
        /// The zipped stream waits for both streams to produce an item, and then
        /// returns that pair. If an error happens, then that error will be returned
        /// immediately. If either stream ends then the zipped stream will also end.
        fn zip<S>(self, other: S) -> Zip<Self, S>
            where S: Stream<Error = Self::Error>,
                  Self: Sized,
        {
            zip::new(self, other)
        }

        /// Adapter for chaining two stream.
        ///
        /// The resulting stream emits elements from the first stream, and when
        /// first stream reaches the end, emits the elements from the second stream.
        ///
        /// ```rust
        /// use futures::prelude::*;
        /// use futures::stream;
        ///
        /// let stream1 = stream::iter_result(vec![Ok(10), Err(false)]);
        /// let stream2 = stream::iter_result(vec![Err(true), Ok(20)]);
        /// let mut chain = stream1.chain(stream2).wait();
        ///
        /// assert_eq!(Some(Ok(10)), chain.next());
        /// assert_eq!(Some(Err(false)), chain.next());
        /// assert_eq!(Some(Err(true)), chain.next());
        /// assert_eq!(Some(Ok(20)), chain.next());
        /// assert_eq!(None, chain.next());
        /// ```
        fn chain<S>(self, other: S) -> Chain<Self, S>
            where S: Stream<Item = Self::Item, Error = Self::Error>,
                  Self: Sized
        {
            chain::new(self, other)
        }

        /// Creates a new stream which exposes a `peek` method.
        ///
        /// Calling `peek` returns a reference to the next item in the stream.
        fn peekable(self) -> Peekable<Self>
            where Self: Sized
        {
            peek::new(self)
        }

        /// An adaptor for chunking up items of the stream inside a vector.
        ///
        /// This combinator will attempt to pull items from this stream and buffer
        /// them into a local vector. At most `capacity` items will get buffered
        /// before they're yielded from the returned stream.
        ///
        /// Note that the vectors returned from this iterator may not always have
        /// `capacity` elements. If the underlying stream ended and only a partial
        /// vector was created, it'll be returned. Additionally if an error happens
        /// from the underlying stream then the currently buffered items will be
        /// yielded.
        ///
        /// Errors are passed through the stream unbuffered.
        ///
        /// This method is only available when the `use_std` feature of this
        /// library is activated, and it is activated by default.
        ///
        /// # Panics
        ///
        /// This method will panic of `capacity` is zero.
        #[cfg(feature = "use_std")]
        fn chunks(self, capacity: usize) -> Chunks<Self>
            where Self: Sized
        {
            chunks::new(self, capacity)
        }

        /// Creates a stream that selects the next element from either this stream
        /// or the provided one, whichever is ready first.
        ///
        /// This combinator will attempt to pull items from both streams. Each
        /// stream will be polled in a round-robin fashion, and whenever a stream is
        /// ready to yield an item that item is yielded.
        ///
        /// The `select` function is similar to `merge` except that it requires both
        /// streams to have the same item and error types.
        ///
        /// Error are passed through from either stream.
        fn select<S>(self, other: S) -> Select<Self, S>
            where S: Stream<Item = Self::Item, Error = Self::Error>,
                  Self: Sized,
        {
            select::new(self, other)
        }

        /// A future that completes after the given stream has been fully processed
        /// into the sink, including flushing.
        ///
        /// This future will drive the stream to keep producing items until it is
        /// exhausted, sending each item to the sink. It will complete once both the
        /// stream is exhausted, and the sink has fully processed received item,
        /// flushed successfully, and closed successfully.
        ///
        /// Doing `stream.forward(sink)` is roughly equivalent to
        /// `sink.send_all(stream)`. The returned future will exhaust all items from
        /// `self`, sending them all to `sink`. Furthermore the `sink` will be
        /// closed and flushed.
        ///
        /// On completion, the pair `(stream, sink)` is returned.
        fn forward<S>(self, sink: S) -> Forward<Self, S>
            where S: Sink<SinkItem = Self::Item>,
                  Self::Error: From<S::SinkError>,
                  Self: Sized
        {
            forward::new(self, sink)
        }

        /// Splits this `Stream + Sink` object into separate `Stream` and `Sink`
        /// objects.
        ///
        /// This can be useful when you want to split ownership between tasks, or
        /// allow direct interaction between the two objects (e.g. via
        /// `Sink::send_all`).
        ///
        /// This method is only available when the `use_std` feature of this
        /// library is activated, and it is activated by default.
        #[cfg(feature = "use_std")]
        fn split(self) -> (SplitSink<Self>, SplitStream<Self>)
            where Self: super::sink::Sink + Sized
        {
            split::split(self)
        }

        /// Do something with each item of this stream, afterwards passing it on.
        ///
        /// This is similar to the `Iterator::inspect` method in the standard
        /// library where it allows easily inspecting each value as it passes
        /// through the stream, for example to debug what's going on.
        fn inspect<F>(self, f: F) -> Inspect<Self, F>
            where F: FnMut(&Self::Item),
                  Self: Sized,
        {
            inspect::new(self, f)
        }

        /// Do something with the error of this stream, afterwards passing it on.
        ///
        /// This is similar to the `Stream::inspect` method where it allows
        /// easily inspecting the error as it passes through the stream, for
        /// example to debug what's going on.
        fn inspect_err<F>(self, f: F) -> InspectErr<Self, F>
            where F: FnMut(&Self::Error),
                  Self: Sized,
        {
            inspect_err::new(self, f)
        }
    }

    impl<'a, S: ?Sized + Stream> Stream for &'a mut S {
        type Item = S::Item;
        type Error = S::Error;

        fn poll(&mut self) -> Poll<Option<Self::Item>, Self::Error> {
            (**self).poll()
        }
    }

    /// Converts a list of futures into a `Stream` of results from the futures.
    ///
    /// This function will take an list of futures (e.g. a vector, an iterator,
    /// etc), and return a stream. The stream will yield items as they become
    /// available on the futures internally, in the order that they become
    /// available. This function is similar to `buffer_unordered` in that it may
    /// return items in a different order than in the list specified.
    ///
    /// Note that the returned set can also be used to dynamically push more
    /// futures into the set as they become available.
    #[cfg(feature = "use_std")]
    pub fn futures_unordered<I>(futures: I) -> FuturesUnordered<<I::Item as IntoFuture>::Future>
        where I: IntoIterator,
            I::Item: IntoFuture
    {
        let mut set = FuturesUnordered::new();

        for future in futures {
            set.push(future.into_future());
        }

        return set
    }

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