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use {Parcel, Error, ErrorKind, Settings};

use std::io::prelude::*;

/// A type that does not have any protocol serialization implemented.
///
/// # Behaviour
///
/// If any unimplemented parcel is read, an error of type
/// `UnimplementedParcel` is returned. This allows clients to
/// handle unimplemented data gracefully.
///
/// If you attempt to write an unimplemented parcel, the
/// program panics. It makes sense to do error handling on
/// unimplemented types that are read from remote machines,
/// but it does not make sense to allow undefined data to be sent.
#[derive(Copy, Clone, Debug, PartialEq, Eq, PartialOrd, Ord, Hash)]
pub struct Unimplemented;

impl Parcel for Unimplemented
{
    const TYPE_NAME: &'static str = "Unimplemented";

    fn read(_: &mut Read,
            _: &Settings) -> Result<Self, Error> {
        Err(ErrorKind::UnimplementedParcel(Self::TYPE_NAME).into())
    }

    fn write(&self, _: &mut Write,
             _: &Settings) -> Result<(), Error> {
        unimplemented!();
    }
}