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#![cfg_attr(test, feature(plugin))]
#![cfg_attr(test, plugin(clippy))]
#![feature(box_syntax)]

use std::fmt;
use std::ops::Deref;

/// Like `ToOwned`, boxing types instead of converting them into different types altogether.
pub trait ToBox {
    /// Creates a boxed version from borrowed data, usually by cloning.
    fn to_box(&self) -> Box<Self>;
}
impl<T: 'static + ?Sized> ToBox for T
    where for<'a> &'a T: Into<Box<T>>
{
    fn to_box(&self) -> Box<T> {
        self.into()
    }
}

/// Like a `Cow`, using `ToBox` instead of `ToBoxed`.
pub enum Bow<'a, T: 'a + ToBox + ?Sized> {
    /// Borrowed data.
    Borrowed(&'a T),

    /// Boxed data.
    Boxed(Box<T>),
}

impl<'a, T: 'a + ToBox + ?Sized> Bow<'a, T> {
    /// Acquires a mutable reference to the data.
    ///
    /// Boxes the data if it is not already boxed.
    pub fn to_mut(&mut self) -> &mut T {
        match *self {
            Bow::Borrowed(val) => {
                *self = Bow::Boxed(val.to_box());
                match *self {
                    Bow::Borrowed(..) => unreachable!(),
                    Bow::Boxed(ref mut val) => val,
                }
            }
            Bow::Boxed(ref mut val) => val,
        }
    }

    /// Extracts the data as a box.
    ///
    /// Boxes the data if it is not already boxed.
    pub fn into_box(self) -> Box<T> {
        match self {
            Bow::Borrowed(val) => val.to_box(),
            Bow::Boxed(val) => val,
        }
    }
}

impl<'a, T: ToBox + ?Sized> Clone for Bow<'a, T> {
    fn clone(&self) -> Self {
        match *self {
            Bow::Borrowed(val) => Bow::Borrowed(val),
            Bow::Boxed(ref val) => Bow::Boxed(val.to_box()),
        }
    }
}

impl<'a, T: 'a + ToBox + ?Sized> Deref for Bow<'a, T> {
    type Target = T;
    fn deref(&self) -> &T {
        match *self {
            Bow::Borrowed(val) => val,
            Bow::Boxed(ref val) => val,
        }
    }
}

impl<'a, T: 'a + ToBox + fmt::Debug + ?Sized> fmt::Debug for Bow<'a, T> {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        match *self {
            Bow::Boxed(ref val) => fmt::Debug::fmt(val, f),
            Bow::Borrowed(val) => fmt::Debug::fmt(val, f),
        }
    }
}

impl<'a, T: 'a + ToBox + fmt::Display + ?Sized> fmt::Display for Bow<'a, T> {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        match *self {
            Bow::Boxed(ref val) => fmt::Display::fmt(val, f),
            Bow::Borrowed(val) => fmt::Display::fmt(val, f),
        }
    }
}

impl<T: 'static + ToBox + ?Sized> Default for Bow<'static, T>
    where &'static T: Default
{
    fn default() -> Bow<'static, T> {
        Bow::Borrowed(Default::default())
    }
}

impl<'a, T: 'a + ToBox + ?Sized> AsRef<T> for Bow<'a, T> {
    fn as_ref(&self) -> &T {
        self
    }
}

impl<'a, T: 'a + ToBox + ?Sized> From<&'a T> for Bow<'a, T> {
    fn from(val: &'a T) -> Bow<'a, T> {
        Bow::Borrowed(val)
    }
}

impl<'a, T: 'a + ToBox + ?Sized> From<Box<T>> for Bow<'a, T> {
    fn from(val: Box<T>) -> Bow<'a, T> {
        Bow::Boxed(val)
    }
}