Adding upstream version 124.0.1.upstream/124.0.1

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1471 insertions, 0 deletions

diff --git a/third_party/rust/either/src/lib.rs b/third_party/rust/either/src/lib.rs
new file mode 100644
index 0000000000..9a271c3513
--- /dev/null
+++ b/third_party/rust/either/src/lib.rs
@@ -0,0 +1,1471 @@
+//! The enum [`Either`] with variants `Left` and `Right` is a general purpose
+//! sum type with two cases.
+//!
+//! [`Either`]: enum.Either.html
+//!
+//! **Crate features:**
+//!
+//! * `"use_std"`
+//! Enabled by default. Disable to make the library `#![no_std]`.
+//!
+//! * `"serde"`
+//! Disabled by default. Enable to `#[derive(Serialize, Deserialize)]` for `Either`
+//!
+
+#![doc(html_root_url = "https://docs.rs/either/1/")]
+#![no_std]
+
+#[cfg(any(test, feature = "use_std"))]
+extern crate std;
+
+#[cfg(feature = "serde")]
+pub mod serde_untagged;
+
+#[cfg(feature = "serde")]
+pub mod serde_untagged_optional;
+
+use core::convert::{AsMut, AsRef};
+use core::fmt;
+use core::future::Future;
+use core::iter;
+use core::ops::Deref;
+use core::ops::DerefMut;
+use core::pin::Pin;
+
+#[cfg(any(test, feature = "use_std"))]
+use std::error::Error;
+#[cfg(any(test, feature = "use_std"))]
+use std::io::{self, BufRead, Read, Seek, SeekFrom, Write};
+
+pub use crate::Either::{Left, Right};
+
+/// The enum `Either` with variants `Left` and `Right` is a general purpose
+/// sum type with two cases.
+///
+/// The `Either` type is symmetric and treats its variants the same way, without
+/// preference.
+/// (For representing success or error, use the regular `Result` enum instead.)
+#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
+#[derive(Copy, PartialEq, Eq, PartialOrd, Ord, Hash, Debug)]
+pub enum Either<L, R> {
+    /// A value of type `L`.
+    Left(L),
+    /// A value of type `R`.
+    Right(R),
+}
+
+/// Evaluate the provided expression for both [`Either::Left`] and [`Either::Right`].
+///
+/// This macro is useful in cases where both sides of [`Either`] can be interacted with
+/// in the same way even though the don't share the same type.
+///
+/// Syntax: `either::for_both!(` *expression* `,` *pattern* `=>` *expression* `)`
+///
+/// # Example
+///
+/// ```
+/// use either::Either;
+///
+/// fn length(owned_or_borrowed: Either<String, &'static str>) -> usize {
+///     either::for_both!(owned_or_borrowed, s => s.len())
+/// }
+///
+/// fn main() {
+///     let borrowed = Either::Right("Hello world!");
+///     let owned = Either::Left("Hello world!".to_owned());
+///
+///     assert_eq!(length(borrowed), 12);
+///     assert_eq!(length(owned), 12);
+/// }
+/// ```
+#[macro_export]
+macro_rules! for_both {
+    ($value:expr, $pattern:pat => $result:expr) => {
+        match $value {
+            $crate::Either::Left($pattern) => $result,
+            $crate::Either::Right($pattern) => $result,
+        }
+    };
+}
+
+/// Macro for unwrapping the left side of an `Either`, which fails early
+/// with the opposite side. Can only be used in functions that return
+/// `Either` because of the early return of `Right` that it provides.
+///
+/// See also `try_right!` for its dual, which applies the same just to the
+/// right side.
+///
+/// # Example
+///
+/// ```
+/// use either::{Either, Left, Right};
+///
+/// fn twice(wrapper: Either<u32, &str>) -> Either<u32, &str> {
+///     let value = either::try_left!(wrapper);
+///     Left(value * 2)
+/// }
+///
+/// fn main() {
+///     assert_eq!(twice(Left(2)), Left(4));
+///     assert_eq!(twice(Right("ups")), Right("ups"));
+/// }
+/// ```
+#[macro_export]
+macro_rules! try_left {
+    ($expr:expr) => {
+        match $expr {
+            $crate::Left(val) => val,
+            $crate::Right(err) => return $crate::Right(::core::convert::From::from(err)),
+        }
+    };
+}
+
+/// Dual to `try_left!`, see its documentation for more information.
+#[macro_export]
+macro_rules! try_right {
+    ($expr:expr) => {
+        match $expr {
+            $crate::Left(err) => return $crate::Left(::core::convert::From::from(err)),
+            $crate::Right(val) => val,
+        }
+    };
+}
+
+impl<L: Clone, R: Clone> Clone for Either<L, R> {
+    fn clone(&self) -> Self {
+        match self {
+            Left(inner) => Left(inner.clone()),
+            Right(inner) => Right(inner.clone()),
+        }
+    }
+
+    fn clone_from(&mut self, source: &Self) {
+        match (self, source) {
+            (Left(dest), Left(source)) => dest.clone_from(source),
+            (Right(dest), Right(source)) => dest.clone_from(source),
+            (dest, source) => *dest = source.clone(),
+        }
+    }
+}
+
+impl<L, R> Either<L, R> {
+    /// Return true if the value is the `Left` variant.
+    ///
+    /// ```
+    /// use either::*;
+    ///
+    /// let values = [Left(1), Right("the right value")];
+    /// assert_eq!(values[0].is_left(), true);
+    /// assert_eq!(values[1].is_left(), false);
+    /// ```
+    pub fn is_left(&self) -> bool {
+        match *self {
+            Left(_) => true,
+            Right(_) => false,
+        }
+    }
+
+    /// Return true if the value is the `Right` variant.
+    ///
+    /// ```
+    /// use either::*;
+    ///
+    /// let values = [Left(1), Right("the right value")];
+    /// assert_eq!(values[0].is_right(), false);
+    /// assert_eq!(values[1].is_right(), true);
+    /// ```
+    pub fn is_right(&self) -> bool {
+        !self.is_left()
+    }
+
+    /// Convert the left side of `Either<L, R>` to an `Option<L>`.
+    ///
+    /// ```
+    /// use either::*;
+    ///
+    /// let left: Either<_, ()> = Left("some value");
+    /// assert_eq!(left.left(),  Some("some value"));
+    ///
+    /// let right: Either<(), _> = Right(321);
+    /// assert_eq!(right.left(), None);
+    /// ```
+    pub fn left(self) -> Option<L> {
+        match self {
+            Left(l) => Some(l),
+            Right(_) => None,
+        }
+    }
+
+    /// Convert the right side of `Either<L, R>` to an `Option<R>`.
+    ///
+    /// ```
+    /// use either::*;
+    ///
+    /// let left: Either<_, ()> = Left("some value");
+    /// assert_eq!(left.right(),  None);
+    ///
+    /// let right: Either<(), _> = Right(321);
+    /// assert_eq!(right.right(), Some(321));
+    /// ```
+    pub fn right(self) -> Option<R> {
+        match self {
+            Left(_) => None,
+            Right(r) => Some(r),
+        }
+    }
+
+    /// Convert `&Either<L, R>` to `Either<&L, &R>`.
+    ///
+    /// ```
+    /// use either::*;
+    ///
+    /// let left: Either<_, ()> = Left("some value");
+    /// assert_eq!(left.as_ref(), Left(&"some value"));
+    ///
+    /// let right: Either<(), _> = Right("some value");
+    /// assert_eq!(right.as_ref(), Right(&"some value"));
+    /// ```
+    pub fn as_ref(&self) -> Either<&L, &R> {
+        match *self {
+            Left(ref inner) => Left(inner),
+            Right(ref inner) => Right(inner),
+        }
+    }
+
+    /// Convert `&mut Either<L, R>` to `Either<&mut L, &mut R>`.
+    ///
+    /// ```
+    /// use either::*;
+    ///
+    /// fn mutate_left(value: &mut Either<u32, u32>) {
+    ///     if let Some(l) = value.as_mut().left() {
+    ///         *l = 999;
+    ///     }
+    /// }
+    ///
+    /// let mut left = Left(123);
+    /// let mut right = Right(123);
+    /// mutate_left(&mut left);
+    /// mutate_left(&mut right);
+    /// assert_eq!(left, Left(999));
+    /// assert_eq!(right, Right(123));
+    /// ```
+    pub fn as_mut(&mut self) -> Either<&mut L, &mut R> {
+        match *self {
+            Left(ref mut inner) => Left(inner),
+            Right(ref mut inner) => Right(inner),
+        }
+    }
+
+    /// Convert `Pin<&Either<L, R>>` to `Either<Pin<&L>, Pin<&R>>`,
+    /// pinned projections of the inner variants.
+    pub fn as_pin_ref(self: Pin<&Self>) -> Either<Pin<&L>, Pin<&R>> {
+        // SAFETY: We can use `new_unchecked` because the `inner` parts are
+        // guaranteed to be pinned, as they come from `self` which is pinned.
+        unsafe {
+            match *Pin::get_ref(self) {
+                Left(ref inner) => Left(Pin::new_unchecked(inner)),
+                Right(ref inner) => Right(Pin::new_unchecked(inner)),
+            }
+        }
+    }
+
+    /// Convert `Pin<&mut Either<L, R>>` to `Either<Pin<&mut L>, Pin<&mut R>>`,
+    /// pinned projections of the inner variants.
+    pub fn as_pin_mut(self: Pin<&mut Self>) -> Either<Pin<&mut L>, Pin<&mut R>> {
+        // SAFETY: `get_unchecked_mut` is fine because we don't move anything.
+        // We can use `new_unchecked` because the `inner` parts are guaranteed
+        // to be pinned, as they come from `self` which is pinned, and we never
+        // offer an unpinned `&mut L` or `&mut R` through `Pin<&mut Self>`. We
+        // also don't have an implementation of `Drop`, nor manual `Unpin`.
+        unsafe {
+            match *Pin::get_unchecked_mut(self) {
+                Left(ref mut inner) => Left(Pin::new_unchecked(inner)),
+                Right(ref mut inner) => Right(Pin::new_unchecked(inner)),
+            }
+        }
+    }
+
+    /// Convert `Either<L, R>` to `Either<R, L>`.
+    ///
+    /// ```
+    /// use either::*;
+    ///
+    /// let left: Either<_, ()> = Left(123);
+    /// assert_eq!(left.flip(), Right(123));
+    ///
+    /// let right: Either<(), _> = Right("some value");
+    /// assert_eq!(right.flip(), Left("some value"));
+    /// ```
+    pub fn flip(self) -> Either<R, L> {
+        match self {
+            Left(l) => Right(l),
+            Right(r) => Left(r),
+        }
+    }
+
+    /// Apply the function `f` on the value in the `Left` variant if it is present rewrapping the
+    /// result in `Left`.
+    ///
+    /// ```
+    /// use either::*;
+    ///
+    /// let left: Either<_, u32> = Left(123);
+    /// assert_eq!(left.map_left(|x| x * 2), Left(246));
+    ///
+    /// let right: Either<u32, _> = Right(123);
+    /// assert_eq!(right.map_left(|x| x * 2), Right(123));
+    /// ```
+    pub fn map_left<F, M>(self, f: F) -> Either<M, R>
+    where
+        F: FnOnce(L) -> M,
+    {
+        match self {
+            Left(l) => Left(f(l)),
+            Right(r) => Right(r),
+        }
+    }
+
+    /// Apply the function `f` on the value in the `Right` variant if it is present rewrapping the
+    /// result in `Right`.
+    ///
+    /// ```
+    /// use either::*;
+    ///
+    /// let left: Either<_, u32> = Left(123);
+    /// assert_eq!(left.map_right(|x| x * 2), Left(123));
+    ///
+    /// let right: Either<u32, _> = Right(123);
+    /// assert_eq!(right.map_right(|x| x * 2), Right(246));
+    /// ```
+    pub fn map_right<F, S>(self, f: F) -> Either<L, S>
+    where
+        F: FnOnce(R) -> S,
+    {
+        match self {
+            Left(l) => Left(l),
+            Right(r) => Right(f(r)),
+        }
+    }
+
+    /// Apply one of two functions depending on contents, unifying their result. If the value is
+    /// `Left(L)` then the first function `f` is applied; if it is `Right(R)` then the second
+    /// function `g` is applied.
+    ///
+    /// ```
+    /// use either::*;
+    ///
+    /// fn square(n: u32) -> i32 { (n * n) as i32 }
+    /// fn negate(n: i32) -> i32 { -n }
+    ///
+    /// let left: Either<u32, i32> = Left(4);
+    /// assert_eq!(left.either(square, negate), 16);
+    ///
+    /// let right: Either<u32, i32> = Right(-4);
+    /// assert_eq!(right.either(square, negate), 4);
+    /// ```
+    pub fn either<F, G, T>(self, f: F, g: G) -> T
+    where
+        F: FnOnce(L) -> T,
+        G: FnOnce(R) -> T,
+    {
+        match self {
+            Left(l) => f(l),
+            Right(r) => g(r),
+        }
+    }
+
+    /// Like `either`, but provide some context to whichever of the
+    /// functions ends up being called.
+    ///
+    /// ```
+    /// // In this example, the context is a mutable reference
+    /// use either::*;
+    ///
+    /// let mut result = Vec::new();
+    ///
+    /// let values = vec![Left(2), Right(2.7)];
+    ///
+    /// for value in values {
+    ///     value.either_with(&mut result,
+    ///                       |ctx, integer| ctx.push(integer),
+    ///                       |ctx, real| ctx.push(f64::round(real) as i32));
+    /// }
+    ///
+    /// assert_eq!(result, vec![2, 3]);
+    /// ```
+    pub fn either_with<Ctx, F, G, T>(self, ctx: Ctx, f: F, g: G) -> T
+    where
+        F: FnOnce(Ctx, L) -> T,
+        G: FnOnce(Ctx, R) -> T,
+    {
+        match self {
+            Left(l) => f(ctx, l),
+            Right(r) => g(ctx, r),
+        }
+    }
+
+    /// Apply the function `f` on the value in the `Left` variant if it is present.
+    ///
+    /// ```
+    /// use either::*;
+    ///
+    /// let left: Either<_, u32> = Left(123);
+    /// assert_eq!(left.left_and_then::<_,()>(|x| Right(x * 2)), Right(246));
+    ///
+    /// let right: Either<u32, _> = Right(123);
+    /// assert_eq!(right.left_and_then(|x| Right::<(), _>(x * 2)), Right(123));
+    /// ```
+    pub fn left_and_then<F, S>(self, f: F) -> Either<S, R>
+    where
+        F: FnOnce(L) -> Either<S, R>,
+    {
+        match self {
+            Left(l) => f(l),
+            Right(r) => Right(r),
+        }
+    }
+
+    /// Apply the function `f` on the value in the `Right` variant if it is present.
+    ///
+    /// ```
+    /// use either::*;
+    ///
+    /// let left: Either<_, u32> = Left(123);
+    /// assert_eq!(left.right_and_then(|x| Right(x * 2)), Left(123));
+    ///
+    /// let right: Either<u32, _> = Right(123);
+    /// assert_eq!(right.right_and_then(|x| Right(x * 2)), Right(246));
+    /// ```
+    pub fn right_and_then<F, S>(self, f: F) -> Either<L, S>
+    where
+        F: FnOnce(R) -> Either<L, S>,
+    {
+        match self {
+            Left(l) => Left(l),
+            Right(r) => f(r),
+        }
+    }
+
+    /// Convert the inner value to an iterator.
+    ///
+    /// ```
+    /// use either::*;
+    ///
+    /// let left: Either<_, Vec<u32>> = Left(vec![1, 2, 3, 4, 5]);
+    /// let mut right: Either<Vec<u32>, _> = Right(vec![]);
+    /// right.extend(left.into_iter());
+    /// assert_eq!(right, Right(vec![1, 2, 3, 4, 5]));
+    /// ```
+    #[allow(clippy::should_implement_trait)]
+    pub fn into_iter(self) -> Either<L::IntoIter, R::IntoIter>
+    where
+        L: IntoIterator,
+        R: IntoIterator<Item = L::Item>,
+    {
+        match self {
+            Left(l) => Left(l.into_iter()),
+            Right(r) => Right(r.into_iter()),
+        }
+    }
+
+    /// Return left value or given value
+    ///
+    /// Arguments passed to `left_or` are eagerly evaluated; if you are passing
+    /// the result of a function call, it is recommended to use [`left_or_else`],
+    /// which is lazily evaluated.
+    ///
+    /// [`left_or_else`]: #method.left_or_else
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # use either::*;
+    /// let left: Either<&str, &str> = Left("left");
+    /// assert_eq!(left.left_or("foo"), "left");
+    ///
+    /// let right: Either<&str, &str> = Right("right");
+    /// assert_eq!(right.left_or("left"), "left");
+    /// ```
+    pub fn left_or(self, other: L) -> L {
+        match self {
+            Either::Left(l) => l,
+            Either::Right(_) => other,
+        }
+    }
+
+    /// Return left or a default
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # use either::*;
+    /// let left: Either<String, u32> = Left("left".to_string());
+    /// assert_eq!(left.left_or_default(), "left");
+    ///
+    /// let right: Either<String, u32> = Right(42);
+    /// assert_eq!(right.left_or_default(), String::default());
+    /// ```
+    pub fn left_or_default(self) -> L
+    where
+        L: Default,
+    {
+        match self {
+            Either::Left(l) => l,
+            Either::Right(_) => L::default(),
+        }
+    }
+
+    /// Returns left value or computes it from a closure
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # use either::*;
+    /// let left: Either<String, u32> = Left("3".to_string());
+    /// assert_eq!(left.left_or_else(|_| unreachable!()), "3");
+    ///
+    /// let right: Either<String, u32> = Right(3);
+    /// assert_eq!(right.left_or_else(|x| x.to_string()), "3");
+    /// ```
+    pub fn left_or_else<F>(self, f: F) -> L
+    where
+        F: FnOnce(R) -> L,
+    {
+        match self {
+            Either::Left(l) => l,
+            Either::Right(r) => f(r),
+        }
+    }
+
+    /// Return right value or given value
+    ///
+    /// Arguments passed to `right_or` are eagerly evaluated; if you are passing
+    /// the result of a function call, it is recommended to use [`right_or_else`],
+    /// which is lazily evaluated.
+    ///
+    /// [`right_or_else`]: #method.right_or_else
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # use either::*;
+    /// let right: Either<&str, &str> = Right("right");
+    /// assert_eq!(right.right_or("foo"), "right");
+    ///
+    /// let left: Either<&str, &str> = Left("left");
+    /// assert_eq!(left.right_or("right"), "right");
+    /// ```
+    pub fn right_or(self, other: R) -> R {
+        match self {
+            Either::Left(_) => other,
+            Either::Right(r) => r,
+        }
+    }
+
+    /// Return right or a default
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # use either::*;
+    /// let left: Either<String, u32> = Left("left".to_string());
+    /// assert_eq!(left.right_or_default(), u32::default());
+    ///
+    /// let right: Either<String, u32> = Right(42);
+    /// assert_eq!(right.right_or_default(), 42);
+    /// ```
+    pub fn right_or_default(self) -> R
+    where
+        R: Default,
+    {
+        match self {
+            Either::Left(_) => R::default(),
+            Either::Right(r) => r,
+        }
+    }
+
+    /// Returns right value or computes it from a closure
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # use either::*;
+    /// let left: Either<String, u32> = Left("3".to_string());
+    /// assert_eq!(left.right_or_else(|x| x.parse().unwrap()), 3);
+    ///
+    /// let right: Either<String, u32> = Right(3);
+    /// assert_eq!(right.right_or_else(|_| unreachable!()), 3);
+    /// ```
+    pub fn right_or_else<F>(self, f: F) -> R
+    where
+        F: FnOnce(L) -> R,
+    {
+        match self {
+            Either::Left(l) => f(l),
+            Either::Right(r) => r,
+        }
+    }
+
+    /// Returns the left value
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # use either::*;
+    /// let left: Either<_, ()> = Left(3);
+    /// assert_eq!(left.unwrap_left(), 3);
+    /// ```
+    ///
+    /// # Panics
+    ///
+    /// When `Either` is a `Right` value
+    ///
+    /// ```should_panic
+    /// # use either::*;
+    /// let right: Either<(), _> = Right(3);
+    /// right.unwrap_left();
+    /// ```
+    pub fn unwrap_left(self) -> L
+    where
+        R: core::fmt::Debug,
+    {
+        match self {
+            Either::Left(l) => l,
+            Either::Right(r) => {
+                panic!("called `Either::unwrap_left()` on a `Right` value: {:?}", r)
+            }
+        }
+    }
+
+    /// Returns the right value
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # use either::*;
+    /// let right: Either<(), _> = Right(3);
+    /// assert_eq!(right.unwrap_right(), 3);
+    /// ```
+    ///
+    /// # Panics
+    ///
+    /// When `Either` is a `Left` value
+    ///
+    /// ```should_panic
+    /// # use either::*;
+    /// let left: Either<_, ()> = Left(3);
+    /// left.unwrap_right();
+    /// ```
+    pub fn unwrap_right(self) -> R
+    where
+        L: core::fmt::Debug,
+    {
+        match self {
+            Either::Right(r) => r,
+            Either::Left(l) => panic!("called `Either::unwrap_right()` on a `Left` value: {:?}", l),
+        }
+    }
+
+    /// Returns the left value
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # use either::*;
+    /// let left: Either<_, ()> = Left(3);
+    /// assert_eq!(left.expect_left("value was Right"), 3);
+    /// ```
+    ///
+    /// # Panics
+    ///
+    /// When `Either` is a `Right` value
+    ///
+    /// ```should_panic
+    /// # use either::*;
+    /// let right: Either<(), _> = Right(3);
+    /// right.expect_left("value was Right");
+    /// ```
+    pub fn expect_left(self, msg: &str) -> L
+    where
+        R: core::fmt::Debug,
+    {
+        match self {
+            Either::Left(l) => l,
+            Either::Right(r) => panic!("{}: {:?}", msg, r),
+        }
+    }
+
+    /// Returns the right value
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # use either::*;
+    /// let right: Either<(), _> = Right(3);
+    /// assert_eq!(right.expect_right("value was Left"), 3);
+    /// ```
+    ///
+    /// # Panics
+    ///
+    /// When `Either` is a `Left` value
+    ///
+    /// ```should_panic
+    /// # use either::*;
+    /// let left: Either<_, ()> = Left(3);
+    /// left.expect_right("value was Right");
+    /// ```
+    pub fn expect_right(self, msg: &str) -> R
+    where
+        L: core::fmt::Debug,
+    {
+        match self {
+            Either::Right(r) => r,
+            Either::Left(l) => panic!("{}: {:?}", msg, l),
+        }
+    }
+
+    /// Convert the contained value into `T`
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # use either::*;
+    /// // Both u16 and u32 can be converted to u64.
+    /// let left: Either<u16, u32> = Left(3u16);
+    /// assert_eq!(left.either_into::<u64>(), 3u64);
+    /// let right: Either<u16, u32> = Right(7u32);
+    /// assert_eq!(right.either_into::<u64>(), 7u64);
+    /// ```
+    pub fn either_into<T>(self) -> T
+    where
+        L: Into<T>,
+        R: Into<T>,
+    {
+        match self {
+            Either::Left(l) => l.into(),
+            Either::Right(r) => r.into(),
+        }
+    }
+}
+
+impl<L, R> Either<Option<L>, Option<R>> {
+    /// Factors out `None` from an `Either` of [`Option`].
+    ///
+    /// ```
+    /// use either::*;
+    /// let left: Either<_, Option<String>> = Left(Some(vec![0]));
+    /// assert_eq!(left.factor_none(), Some(Left(vec![0])));
+    ///
+    /// let right: Either<Option<Vec<u8>>, _> = Right(Some(String::new()));
+    /// assert_eq!(right.factor_none(), Some(Right(String::new())));
+    /// ```
+    // TODO(MSRV): doc(alias) was stabilized in Rust 1.48
+    // #[doc(alias = "transpose")]
+    pub fn factor_none(self) -> Option<Either<L, R>> {
+        match self {
+            Left(l) => l.map(Either::Left),
+            Right(r) => r.map(Either::Right),
+        }
+    }
+}
+
+impl<L, R, E> Either<Result<L, E>, Result<R, E>> {
+    /// Factors out a homogenous type from an `Either` of [`Result`].
+    ///
+    /// Here, the homogeneous type is the `Err` type of the [`Result`].
+    ///
+    /// ```
+    /// use either::*;
+    /// let left: Either<_, Result<String, u32>> = Left(Ok(vec![0]));
+    /// assert_eq!(left.factor_err(), Ok(Left(vec![0])));
+    ///
+    /// let right: Either<Result<Vec<u8>, u32>, _> = Right(Ok(String::new()));
+    /// assert_eq!(right.factor_err(), Ok(Right(String::new())));
+    /// ```
+    // TODO(MSRV): doc(alias) was stabilized in Rust 1.48
+    // #[doc(alias = "transpose")]
+    pub fn factor_err(self) -> Result<Either<L, R>, E> {
+        match self {
+            Left(l) => l.map(Either::Left),
+            Right(r) => r.map(Either::Right),
+        }
+    }
+}
+
+impl<T, L, R> Either<Result<T, L>, Result<T, R>> {
+    /// Factors out a homogenous type from an `Either` of [`Result`].
+    ///
+    /// Here, the homogeneous type is the `Ok` type of the [`Result`].
+    ///
+    /// ```
+    /// use either::*;
+    /// let left: Either<_, Result<u32, String>> = Left(Err(vec![0]));
+    /// assert_eq!(left.factor_ok(), Err(Left(vec![0])));
+    ///
+    /// let right: Either<Result<u32, Vec<u8>>, _> = Right(Err(String::new()));
+    /// assert_eq!(right.factor_ok(), Err(Right(String::new())));
+    /// ```
+    // TODO(MSRV): doc(alias) was stabilized in Rust 1.48
+    // #[doc(alias = "transpose")]
+    pub fn factor_ok(self) -> Result<T, Either<L, R>> {
+        match self {
+            Left(l) => l.map_err(Either::Left),
+            Right(r) => r.map_err(Either::Right),
+        }
+    }
+}
+
+impl<T, L, R> Either<(T, L), (T, R)> {
+    /// Factor out a homogeneous type from an either of pairs.
+    ///
+    /// Here, the homogeneous type is the first element of the pairs.
+    ///
+    /// ```
+    /// use either::*;
+    /// let left: Either<_, (u32, String)> = Left((123, vec![0]));
+    /// assert_eq!(left.factor_first().0, 123);
+    ///
+    /// let right: Either<(u32, Vec<u8>), _> = Right((123, String::new()));
+    /// assert_eq!(right.factor_first().0, 123);
+    /// ```
+    pub fn factor_first(self) -> (T, Either<L, R>) {
+        match self {
+            Left((t, l)) => (t, Left(l)),
+            Right((t, r)) => (t, Right(r)),
+        }
+    }
+}
+
+impl<T, L, R> Either<(L, T), (R, T)> {
+    /// Factor out a homogeneous type from an either of pairs.
+    ///
+    /// Here, the homogeneous type is the second element of the pairs.
+    ///
+    /// ```
+    /// use either::*;
+    /// let left: Either<_, (String, u32)> = Left((vec![0], 123));
+    /// assert_eq!(left.factor_second().1, 123);
+    ///
+    /// let right: Either<(Vec<u8>, u32), _> = Right((String::new(), 123));
+    /// assert_eq!(right.factor_second().1, 123);
+    /// ```
+    pub fn factor_second(self) -> (Either<L, R>, T) {
+        match self {
+            Left((l, t)) => (Left(l), t),
+            Right((r, t)) => (Right(r), t),
+        }
+    }
+}
+
+impl<T> Either<T, T> {
+    /// Extract the value of an either over two equivalent types.
+    ///
+    /// ```
+    /// use either::*;
+    ///
+    /// let left: Either<_, u32> = Left(123);
+    /// assert_eq!(left.into_inner(), 123);
+    ///
+    /// let right: Either<u32, _> = Right(123);
+    /// assert_eq!(right.into_inner(), 123);
+    /// ```
+    pub fn into_inner(self) -> T {
+        for_both!(self, inner => inner)
+    }
+
+    /// Map `f` over the contained value and return the result in the
+    /// corresponding variant.
+    ///
+    /// ```
+    /// use either::*;
+    ///
+    /// let value: Either<_, i32> = Right(42);
+    ///
+    /// let other = value.map(|x| x * 2);
+    /// assert_eq!(other, Right(84));
+    /// ```
+    pub fn map<F, M>(self, f: F) -> Either<M, M>
+    where
+        F: FnOnce(T) -> M,
+    {
+        match self {
+            Left(l) => Left(f(l)),
+            Right(r) => Right(f(r)),
+        }
+    }
+}
+
+/// Convert from `Result` to `Either` with `Ok => Right` and `Err => Left`.
+impl<L, R> From<Result<R, L>> for Either<L, R> {
+    fn from(r: Result<R, L>) -> Self {
+        match r {
+            Err(e) => Left(e),
+            Ok(o) => Right(o),
+        }
+    }
+}
+
+/// Convert from `Either` to `Result` with `Right => Ok` and `Left => Err`.
+#[allow(clippy::from_over_into)] // From requires RFC 2451, Rust 1.41
+impl<L, R> Into<Result<R, L>> for Either<L, R> {
+    fn into(self) -> Result<R, L> {
+        match self {
+            Left(l) => Err(l),
+            Right(r) => Ok(r),
+        }
+    }
+}
+
+impl<L, R, A> Extend<A> for Either<L, R>
+where
+    L: Extend<A>,
+    R: Extend<A>,
+{
+    fn extend<T>(&mut self, iter: T)
+    where
+        T: IntoIterator<Item = A>,
+    {
+        for_both!(*self, ref mut inner => inner.extend(iter))
+    }
+}
+
+/// `Either<L, R>` is an iterator if both `L` and `R` are iterators.
+impl<L, R> Iterator for Either<L, R>
+where
+    L: Iterator,
+    R: Iterator<Item = L::Item>,
+{
+    type Item = L::Item;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        for_both!(*self, ref mut inner => inner.next())
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        for_both!(*self, ref inner => inner.size_hint())
+    }
+
+    fn fold<Acc, G>(self, init: Acc, f: G) -> Acc
+    where
+        G: FnMut(Acc, Self::Item) -> Acc,
+    {
+        for_both!(self, inner => inner.fold(init, f))
+    }
+
+    fn for_each<F>(self, f: F)
+    where
+        F: FnMut(Self::Item),
+    {
+        for_both!(self, inner => inner.for_each(f))
+    }
+
+    fn count(self) -> usize {
+        for_both!(self, inner => inner.count())
+    }
+
+    fn last(self) -> Option<Self::Item> {
+        for_both!(self, inner => inner.last())
+    }
+
+    fn nth(&mut self, n: usize) -> Option<Self::Item> {
+        for_both!(*self, ref mut inner => inner.nth(n))
+    }
+
+    fn collect<B>(self) -> B
+    where
+        B: iter::FromIterator<Self::Item>,
+    {
+        for_both!(self, inner => inner.collect())
+    }
+
+    fn partition<B, F>(self, f: F) -> (B, B)
+    where
+        B: Default + Extend<Self::Item>,
+        F: FnMut(&Self::Item) -> bool,
+    {
+        for_both!(self, inner => inner.partition(f))
+    }
+
+    fn all<F>(&mut self, f: F) -> bool
+    where
+        F: FnMut(Self::Item) -> bool,
+    {
+        for_both!(*self, ref mut inner => inner.all(f))
+    }
+
+    fn any<F>(&mut self, f: F) -> bool
+    where
+        F: FnMut(Self::Item) -> bool,
+    {
+        for_both!(*self, ref mut inner => inner.any(f))
+    }
+
+    fn find<P>(&mut self, predicate: P) -> Option<Self::Item>
+    where
+        P: FnMut(&Self::Item) -> bool,
+    {
+        for_both!(*self, ref mut inner => inner.find(predicate))
+    }
+
+    fn find_map<B, F>(&mut self, f: F) -> Option<B>
+    where
+        F: FnMut(Self::Item) -> Option<B>,
+    {
+        for_both!(*self, ref mut inner => inner.find_map(f))
+    }
+
+    fn position<P>(&mut self, predicate: P) -> Option<usize>
+    where
+        P: FnMut(Self::Item) -> bool,
+    {
+        for_both!(*self, ref mut inner => inner.position(predicate))
+    }
+}
+
+impl<L, R> DoubleEndedIterator for Either<L, R>
+where
+    L: DoubleEndedIterator,
+    R: DoubleEndedIterator<Item = L::Item>,
+{
+    fn next_back(&mut self) -> Option<Self::Item> {
+        for_both!(*self, ref mut inner => inner.next_back())
+    }
+
+    // TODO(MSRV): This was stabilized in Rust 1.37
+    // fn nth_back(&mut self, n: usize) -> Option<Self::Item> {
+    //     for_both!(*self, ref mut inner => inner.nth_back(n))
+    // }
+
+    fn rfold<Acc, G>(self, init: Acc, f: G) -> Acc
+    where
+        G: FnMut(Acc, Self::Item) -> Acc,
+    {
+        for_both!(self, inner => inner.rfold(init, f))
+    }
+
+    fn rfind<P>(&mut self, predicate: P) -> Option<Self::Item>
+    where
+        P: FnMut(&Self::Item) -> bool,
+    {
+        for_both!(*self, ref mut inner => inner.rfind(predicate))
+    }
+}
+
+impl<L, R> ExactSizeIterator for Either<L, R>
+where
+    L: ExactSizeIterator,
+    R: ExactSizeIterator<Item = L::Item>,
+{
+    fn len(&self) -> usize {
+        for_both!(*self, ref inner => inner.len())
+    }
+}
+
+impl<L, R> iter::FusedIterator for Either<L, R>
+where
+    L: iter::FusedIterator,
+    R: iter::FusedIterator<Item = L::Item>,
+{
+}
+
+/// `Either<L, R>` is a future if both `L` and `R` are futures.
+impl<L, R> Future for Either<L, R>
+where
+    L: Future,
+    R: Future<Output = L::Output>,
+{
+    type Output = L::Output;
+
+    fn poll(
+        self: Pin<&mut Self>,
+        cx: &mut core::task::Context<'_>,
+    ) -> core::task::Poll<Self::Output> {
+        for_both!(self.as_pin_mut(), inner => inner.poll(cx))
+    }
+}
+
+#[cfg(any(test, feature = "use_std"))]
+/// `Either<L, R>` implements `Read` if both `L` and `R` do.
+///
+/// Requires crate feature `"use_std"`
+impl<L, R> Read for Either<L, R>
+where
+    L: Read,
+    R: Read,
+{
+    fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
+        for_both!(*self, ref mut inner => inner.read(buf))
+    }
+
+    fn read_exact(&mut self, buf: &mut [u8]) -> io::Result<()> {
+        for_both!(*self, ref mut inner => inner.read_exact(buf))
+    }
+
+    fn read_to_end(&mut self, buf: &mut std::vec::Vec<u8>) -> io::Result<usize> {
+        for_both!(*self, ref mut inner => inner.read_to_end(buf))
+    }
+
+    fn read_to_string(&mut self, buf: &mut std::string::String) -> io::Result<usize> {
+        for_both!(*self, ref mut inner => inner.read_to_string(buf))
+    }
+}
+
+#[cfg(any(test, feature = "use_std"))]
+/// `Either<L, R>` implements `Seek` if both `L` and `R` do.
+///
+/// Requires crate feature `"use_std"`
+impl<L, R> Seek for Either<L, R>
+where
+    L: Seek,
+    R: Seek,
+{
+    fn seek(&mut self, pos: SeekFrom) -> io::Result<u64> {
+        for_both!(*self, ref mut inner => inner.seek(pos))
+    }
+}
+
+#[cfg(any(test, feature = "use_std"))]
+/// Requires crate feature `"use_std"`
+impl<L, R> BufRead for Either<L, R>
+where
+    L: BufRead,
+    R: BufRead,
+{
+    fn fill_buf(&mut self) -> io::Result<&[u8]> {
+        for_both!(*self, ref mut inner => inner.fill_buf())
+    }
+
+    fn consume(&mut self, amt: usize) {
+        for_both!(*self, ref mut inner => inner.consume(amt))
+    }
+
+    fn read_until(&mut self, byte: u8, buf: &mut std::vec::Vec<u8>) -> io::Result<usize> {
+        for_both!(*self, ref mut inner => inner.read_until(byte, buf))
+    }
+
+    fn read_line(&mut self, buf: &mut std::string::String) -> io::Result<usize> {
+        for_both!(*self, ref mut inner => inner.read_line(buf))
+    }
+}
+
+#[cfg(any(test, feature = "use_std"))]
+/// `Either<L, R>` implements `Write` if both `L` and `R` do.
+///
+/// Requires crate feature `"use_std"`
+impl<L, R> Write for Either<L, R>
+where
+    L: Write,
+    R: Write,
+{
+    fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
+        for_both!(*self, ref mut inner => inner.write(buf))
+    }
+
+    fn write_all(&mut self, buf: &[u8]) -> io::Result<()> {
+        for_both!(*self, ref mut inner => inner.write_all(buf))
+    }
+
+    fn write_fmt(&mut self, fmt: fmt::Arguments<'_>) -> io::Result<()> {
+        for_both!(*self, ref mut inner => inner.write_fmt(fmt))
+    }
+
+    fn flush(&mut self) -> io::Result<()> {
+        for_both!(*self, ref mut inner => inner.flush())
+    }
+}
+
+impl<L, R, Target> AsRef<Target> for Either<L, R>
+where
+    L: AsRef<Target>,
+    R: AsRef<Target>,
+{
+    fn as_ref(&self) -> &Target {
+        for_both!(*self, ref inner => inner.as_ref())
+    }
+}
+
+macro_rules! impl_specific_ref_and_mut {
+    ($t:ty, $($attr:meta),* ) => {
+        $(#[$attr])*
+        impl<L, R> AsRef<$t> for Either<L, R>
+            where L: AsRef<$t>, R: AsRef<$t>
+        {
+            fn as_ref(&self) -> &$t {
+                for_both!(*self, ref inner => inner.as_ref())
+            }
+        }
+
+        $(#[$attr])*
+        impl<L, R> AsMut<$t> for Either<L, R>
+            where L: AsMut<$t>, R: AsMut<$t>
+        {
+            fn as_mut(&mut self) -> &mut $t {
+                for_both!(*self, ref mut inner => inner.as_mut())
+            }
+        }
+    };
+}
+
+impl_specific_ref_and_mut!(str,);
+impl_specific_ref_and_mut!(
+    ::std::path::Path,
+    cfg(feature = "use_std"),
+    doc = "Requires crate feature `use_std`."
+);
+impl_specific_ref_and_mut!(
+    ::std::ffi::OsStr,
+    cfg(feature = "use_std"),
+    doc = "Requires crate feature `use_std`."
+);
+impl_specific_ref_and_mut!(
+    ::std::ffi::CStr,
+    cfg(feature = "use_std"),
+    doc = "Requires crate feature `use_std`."
+);
+
+impl<L, R, Target> AsRef<[Target]> for Either<L, R>
+where
+    L: AsRef<[Target]>,
+    R: AsRef<[Target]>,
+{
+    fn as_ref(&self) -> &[Target] {
+        for_both!(*self, ref inner => inner.as_ref())
+    }
+}
+
+impl<L, R, Target> AsMut<Target> for Either<L, R>
+where
+    L: AsMut<Target>,
+    R: AsMut<Target>,
+{
+    fn as_mut(&mut self) -> &mut Target {
+        for_both!(*self, ref mut inner => inner.as_mut())
+    }
+}
+
+impl<L, R, Target> AsMut<[Target]> for Either<L, R>
+where
+    L: AsMut<[Target]>,
+    R: AsMut<[Target]>,
+{
+    fn as_mut(&mut self) -> &mut [Target] {
+        for_both!(*self, ref mut inner => inner.as_mut())
+    }
+}
+
+impl<L, R> Deref for Either<L, R>
+where
+    L: Deref,
+    R: Deref<Target = L::Target>,
+{
+    type Target = L::Target;
+
+    fn deref(&self) -> &Self::Target {
+        for_both!(*self, ref inner => &**inner)
+    }
+}
+
+impl<L, R> DerefMut for Either<L, R>
+where
+    L: DerefMut,
+    R: DerefMut<Target = L::Target>,
+{
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        for_both!(*self, ref mut inner => &mut *inner)
+    }
+}
+
+#[cfg(any(test, feature = "use_std"))]
+/// `Either` implements `Error` if *both* `L` and `R` implement it.
+impl<L, R> Error for Either<L, R>
+where
+    L: Error,
+    R: Error,
+{
+    fn source(&self) -> Option<&(dyn Error + 'static)> {
+        for_both!(*self, ref inner => inner.source())
+    }
+
+    #[allow(deprecated)]
+    fn description(&self) -> &str {
+        for_both!(*self, ref inner => inner.description())
+    }
+
+    #[allow(deprecated)]
+    fn cause(&self) -> Option<&dyn Error> {
+        for_both!(*self, ref inner => inner.cause())
+    }
+}
+
+impl<L, R> fmt::Display for Either<L, R>
+where
+    L: fmt::Display,
+    R: fmt::Display,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        for_both!(*self, ref inner => inner.fmt(f))
+    }
+}
+
+#[test]
+fn basic() {
+    let mut e = Left(2);
+    let r = Right(2);
+    assert_eq!(e, Left(2));
+    e = r;
+    assert_eq!(e, Right(2));
+    assert_eq!(e.left(), None);
+    assert_eq!(e.right(), Some(2));
+    assert_eq!(e.as_ref().right(), Some(&2));
+    assert_eq!(e.as_mut().right(), Some(&mut 2));
+}
+
+#[test]
+fn macros() {
+    use std::string::String;
+
+    fn a() -> Either<u32, u32> {
+        let x: u32 = try_left!(Right(1337u32));
+        Left(x * 2)
+    }
+    assert_eq!(a(), Right(1337));
+
+    fn b() -> Either<String, &'static str> {
+        Right(try_right!(Left("foo bar")))
+    }
+    assert_eq!(b(), Left(String::from("foo bar")));
+}
+
+#[test]
+fn deref() {
+    use std::string::String;
+
+    fn is_str(_: &str) {}
+    let value: Either<String, &str> = Left(String::from("test"));
+    is_str(&*value);
+}
+
+#[test]
+fn iter() {
+    let x = 3;
+    let mut iter = match x {
+        3 => Left(0..10),
+        _ => Right(17..),
+    };
+
+    assert_eq!(iter.next(), Some(0));
+    assert_eq!(iter.count(), 9);
+}
+
+#[test]
+fn seek() {
+    use std::io;
+
+    let use_empty = false;
+    let mut mockdata = [0x00; 256];
+    for i in 0..256 {
+        mockdata[i] = i as u8;
+    }
+
+    let mut reader = if use_empty {
+        // Empty didn't impl Seek until Rust 1.51
+        Left(io::Cursor::new([]))
+    } else {
+        Right(io::Cursor::new(&mockdata[..]))
+    };
+
+    let mut buf = [0u8; 16];
+    assert_eq!(reader.read(&mut buf).unwrap(), buf.len());
+    assert_eq!(buf, mockdata[..buf.len()]);
+
+    // the first read should advance the cursor and return the next 16 bytes thus the `ne`
+    assert_eq!(reader.read(&mut buf).unwrap(), buf.len());
+    assert_ne!(buf, mockdata[..buf.len()]);
+
+    // if the seek operation fails it should read 16..31 instead of 0..15
+    reader.seek(io::SeekFrom::Start(0)).unwrap();
+    assert_eq!(reader.read(&mut buf).unwrap(), buf.len());
+    assert_eq!(buf, mockdata[..buf.len()]);
+}
+
+#[test]
+fn read_write() {
+    use std::io;
+
+    let use_stdio = false;
+    let mockdata = [0xff; 256];
+
+    let mut reader = if use_stdio {
+        Left(io::stdin())
+    } else {
+        Right(&mockdata[..])
+    };
+
+    let mut buf = [0u8; 16];
+    assert_eq!(reader.read(&mut buf).unwrap(), buf.len());
+    assert_eq!(&buf, &mockdata[..buf.len()]);
+
+    let mut mockbuf = [0u8; 256];
+    let mut writer = if use_stdio {
+        Left(io::stdout())
+    } else {
+        Right(&mut mockbuf[..])
+    };
+
+    let buf = [1u8; 16];
+    assert_eq!(writer.write(&buf).unwrap(), buf.len());
+}
+
+#[test]
+#[allow(deprecated)]
+fn error() {
+    let invalid_utf8 = b"\xff";
+    let res = if let Err(error) = ::std::str::from_utf8(invalid_utf8) {
+        Err(Left(error))
+    } else if let Err(error) = "x".parse::<i32>() {
+        Err(Right(error))
+    } else {
+        Ok(())
+    };
+    assert!(res.is_err());
+    res.unwrap_err().description(); // make sure this can be called
+}
+
+/// A helper macro to check if AsRef and AsMut are implemented for a given type.
+macro_rules! check_t {
+    ($t:ty) => {{
+        fn check_ref<T: AsRef<$t>>() {}
+        fn propagate_ref<T1: AsRef<$t>, T2: AsRef<$t>>() {
+            check_ref::<Either<T1, T2>>()
+        }
+        fn check_mut<T: AsMut<$t>>() {}
+        fn propagate_mut<T1: AsMut<$t>, T2: AsMut<$t>>() {
+            check_mut::<Either<T1, T2>>()
+        }
+    }};
+}
+
+// This "unused" method is here to ensure that compilation doesn't fail on given types.
+fn _unsized_ref_propagation() {
+    check_t!(str);
+
+    fn check_array_ref<T: AsRef<[Item]>, Item>() {}
+    fn check_array_mut<T: AsMut<[Item]>, Item>() {}
+
+    fn propagate_array_ref<T1: AsRef<[Item]>, T2: AsRef<[Item]>, Item>() {
+        check_array_ref::<Either<T1, T2>, _>()
+    }
+
+    fn propagate_array_mut<T1: AsMut<[Item]>, T2: AsMut<[Item]>, Item>() {
+        check_array_mut::<Either<T1, T2>, _>()
+    }
+}
+
+// This "unused" method is here to ensure that compilation doesn't fail on given types.
+#[cfg(feature = "use_std")]
+fn _unsized_std_propagation() {
+    check_t!(::std::path::Path);
+    check_t!(::std::ffi::OsStr);
+    check_t!(::std::ffi::CStr);
+}