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    use crate::{Interest, Registry, Token};

    use std::io;

    /// An event source that may be registered with [`Registry`].
    ///
    /// Types that implement `event::Source` can be registered with
    /// `Registry`. Users of Mio **should not** use the `event::Source` trait
    /// functions directly. Instead, the equivalent functions on `Registry` should
    /// be used.
    ///
    /// See [`Registry`] for more details.
    ///
    /// [`Registry`]: ../struct.Registry.html
    ///
    /// # Implementing `event::Source`
    ///
    /// Event sources are always backed by system handles, such as sockets or other
    /// system handles. These `event::Source`s will be monitored by the system
    /// selector. An implementation of `Source` will almost always delegates to a
    /// lower level handle. Examples of this are [`TcpStream`]s, or the *unix only*
    /// [`SourceFd`].
    ///
    /// [`TcpStream`]: ../net/struct.TcpStream.html
    /// [`SourceFd`]: ../unix/struct.SourceFd.html
    ///
    /// # Dropping `event::Source`s
    ///
    /// All `event::Source`s, unless otherwise specified, need to be [deregistered]
    /// before being dropped for them to not leak resources. This goes against the
    /// normal drop behaviour of types in Rust which cleanup after themselves, e.g.
    /// a `File` will close itself. However since deregistering needs access to
    /// [`Registry`] this cannot be done while being dropped.
    ///
    /// [deregistered]: ../struct.Registry.html#method.deregister
    ///
    /// # Examples
    ///
    /// Implementing `Source` on a struct containing a socket:
    ///
    #[cfg_attr(all(feature = "os-poll", features = "net"), doc = "```")]
    #[cfg_attr(not(all(feature = "os-poll", features = "net")), doc = "```ignore")]
    /// use mio::{Interest, Registry, Token};
    /// use mio::event::Source;
    /// use mio::net::TcpStream;
    ///
    /// use std::io;
    ///
    /// # #[allow(dead_code)]
    /// pub struct MySource {
    ///     socket: TcpStream,
    /// }
    ///
    /// impl Source for MySource {
    ///     fn register(&mut self, registry: &Registry, token: Token, interests: Interest)
    ///         -> io::Result<()>
    ///     {
    ///         // Delegate the `register` call to `socket`
    ///         self.socket.register(registry, token, interests)
    ///     }
    ///
    ///     fn reregister(&mut self, registry: &Registry, token: Token, interests: Interest)
    ///         -> io::Result<()>
    ///     {
    ///         // Delegate the `reregister` call to `socket`
    ///         self.socket.reregister(registry, token, interests)
    ///     }
    ///
    ///     fn deregister(&mut self, registry: &Registry) -> io::Result<()> {
    ///         // Delegate the `deregister` call to `socket`
    ///         self.socket.deregister(registry)
    ///     }
    /// }
    /// ```
    pub trait Source {
        /// Register `self` with the given `Registry` instance.
        ///
        /// This function should not be called directly. Use [`Registry::register`]
        /// instead. Implementors should handle registration by delegating the call
        /// to another `Source` type.
        ///
        /// [`Registry::register`]: ../struct.Registry.html#method.register
        fn register(
            &mut self,
            registry: &Registry,
            token: Token,
            interests: Interest,
        ) -> io::Result<()>;

        /// Re-register `self` with the given `Registry` instance.
        ///
        /// This function should not be called directly. Use
        /// [`Registry::reregister`] instead. Implementors should handle
        /// re-registration by either delegating the call to another `Source` type.
        ///
        /// [`Registry::reregister`]: ../struct.Registry.html#method.reregister
        fn reregister(
            &mut self,
            registry: &Registry,
            token: Token,
            interests: Interest,
        ) -> io::Result<()>;

        /// Deregister `self` from the given `Registry` instance.
        ///
        /// This function should not be called directly. Use
        /// [`Registry::deregister`] instead. Implementors should handle
        /// deregistration by delegating the call to another `Source` type.
        ///
        /// [`Registry::deregister`]: ../struct.Registry.html#method.deregister
        fn deregister(&mut self, registry: &Registry) -> io::Result<()>;
    }

    impl<T> Source for Box<T>
    where
        T: Source + ?Sized,
    {
        fn register(
            &mut self,
            registry: &Registry,
            token: Token,
            interests: Interest,
        ) -> io::Result<()> {
            (&mut **self).register(registry, token, interests)
        }

        fn reregister(
            &mut self,
            registry: &Registry,
            token: Token,
            interests: Interest,
        ) -> io::Result<()> {
            (&mut **self).reregister(registry, token, interests)
        }

        fn deregister(&mut self, registry: &Registry) -> io::Result<()> {
            (&mut **self).deregister(registry)
        }
    }