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diff --git a/vendor/yoke/src/either.rs b/vendor/yoke/src/either.rs
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+// 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::borrow::Cow;
+/// 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)]
+#[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>,
+{
+    type Target = T;
+    fn deref(&self) -> &T {
+        use EitherCart::*;
+        match self {
+            A(a) => a.deref(),
+            B(b) => b.deref(),
+        }
+    }
+}
+
+// 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>,
+{
+}
+
+// Safe because both sub-types implement the trait.
+unsafe impl<C0, C1> CloneableCart for EitherCart<C0, C1>
+where
+    C0: CloneableCart,
+    C1: CloneableCart,
+{
+}