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    //! Channel that never delivers messages.
    //!
    //! Messages cannot be sent into this kind of channel.

    use std::marker::PhantomData;
    use std::time::Instant;

    use context::Context;
    use err::{RecvTimeoutError, TryRecvError};
    use select::{Operation, SelectHandle, Token};
    use utils;

    /// This flavor doesn't need a token.
    pub type NeverToken = ();

    /// Channel that never delivers messages.
    pub struct Channel<T> {
        _marker: PhantomData<T>,
    }

    impl<T> Channel<T> {
        /// Creates a channel that never delivers messages.
        #[inline]
        pub fn new() -> Self {
            Channel {
                _marker: PhantomData,
            }
        }

        /// Attempts to receive a message without blocking.
        #[inline]
        pub fn try_recv(&self) -> Result<T, TryRecvError> {
            Err(TryRecvError::Empty)
        }

        /// Receives a message from the channel.
        #[inline]
        pub fn recv(&self, deadline: Option<Instant>) -> Result<T, RecvTimeoutError> {
            utils::sleep_until(deadline);
            Err(RecvTimeoutError::Timeout)
        }

        /// Reads a message from the channel.
        #[inline]
        pub unsafe fn read(&self, _token: &mut Token) -> Result<T, ()> {
            Err(())
        }

        /// Returns `true` if the channel is empty.
        #[inline]
        pub fn is_empty(&self) -> bool {
            true
        }

        /// Returns `true` if the channel is full.
        #[inline]
        pub fn is_full(&self) -> bool {
            true
        }

        /// Returns the number of messages in the channel.
        #[inline]
        pub fn len(&self) -> usize {
            0
        }

        /// Returns the capacity of the channel.
        #[inline]
        pub fn capacity(&self) -> Option<usize> {
            Some(0)
        }
    }

    impl<T> SelectHandle for Channel<T> {
        #[inline]
        fn try_select(&self, _token: &mut Token) -> bool {
            false
        }

        #[inline]
        fn deadline(&self) -> Option<Instant> {
            None
        }

        #[inline]
        fn register(&self, _oper: Operation, _cx: &Context) -> bool {
            self.is_ready()
        }

        #[inline]
        fn unregister(&self, _oper: Operation) {}

        #[inline]
        fn accept(&self, token: &mut Token, _cx: &Context) -> bool {
            self.try_select(token)
        }

        #[inline]
        fn is_ready(&self) -> bool {
            false
        }

        #[inline]
        fn watch(&self, _oper: Operation, _cx: &Context) -> bool {
            self.is_ready()
        }

        #[inline]
        fn unwatch(&self, _oper: Operation) {}
    }

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