// This file is part of ICU4X. For terms of use, please see the file

// called LICENSE at the top level of the ICU4X source tree

// (online at: https://github.com/unicode-org/icu4x/blob/main/LICENSE ).

//! Types to enable polymorphic carts.

use crate::CloneableCart;

use core::ops::Deref;

use stable_deref_trait::StableDeref;

/// A cart that can be one type or the other. Enables ergonomic polymorphic carts.

///

/// `EitherCart` enables yokes originating from different data sources and therefore

/// having different cart types to be merged into the same yoke type, but still being

/// able to recover the original cart type if necessary.

///

/// All relevant Cart traits are implemented for `EitherCart`, and carts can be

/// safely wrapped in an `EitherCart`.

///

/// Also see [`Yoke::erase_box_cart()`](crate::Yoke::erase_box_cart).

///

/// # Examples

///

/// ```

/// use std::rc::Rc;

/// use yoke::either::EitherCart;

/// use yoke::Yoke;

///

/// let y1: Yoke<&'static str, Rc<str>> =

///     Yoke::attach_to_zero_copy_cart("reference counted hello world".into());

///

/// let y2: Yoke<&'static str, &str> = Yoke::attach_to_zero_copy_cart("borrowed hello world");

///

/// type CombinedYoke<'a> = Yoke<&'static str, EitherCart<Rc<str>, &'a str>>;

///

/// // Both yokes can be combined into a single yoke type despite different carts

/// let y3: CombinedYoke = y1.wrap_cart_in_either_a();

/// let y4: CombinedYoke = y2.wrap_cart_in_either_b();

///

/// assert_eq!(*y3.get(), "reference counted hello world");

/// assert_eq!(*y4.get(), "borrowed hello world");

///

/// // The resulting yoke is cloneable if both cart types implement CloneableCart

/// let y5 = y4.clone();

/// assert_eq!(*y5.get(), "borrowed hello world");

/// ```

#[derive(Clone, PartialEq, Eq, Debug)]

#[allow(clippy::exhaustive_enums)] // stable

pub enum EitherCart<C0, C1> {

    A(C0),

    B(C1),

}

impl<C0, C1, T> Deref for EitherCart<C0, C1>

where

    C0: Deref<Target = T>,

    C1: Deref<Target = T>,

    T: ?Sized,

{

    type Target = T;

    fn deref(&self) -> &T {

        use EitherCart::*;

        match self {

            A(a) => a.deref(),

            B(b) => b.deref(),

        }

    }

}

// Safety: Safe because both sub-types implement the trait.

unsafe impl<C0, C1, T> StableDeref for EitherCart<C0, C1>

where

    C0: StableDeref,

    C1: StableDeref,

    C0: Deref<Target = T>,

    C1: Deref<Target = T>,

    T: ?Sized,

{

}

// Safety: Safe because both sub-types implement the trait.

unsafe impl<C0, C1> CloneableCart for EitherCart<C0, C1>

where

    C0: CloneableCart,

    C1: CloneableCart,

{

}