# Enum itertools::Either [−] [src]

```pub enum Either<L, R> {
Left(L),
Right(R),
}```

`Either` represents an alternative holding one value out of either of the two possible values.

`Either` is a general purpose sum type of two parts. For representing success or error, use the regular `Result<T, E>` instead.

## Variants

A value of type `L`.

A value of type `R`.

## Methods

### `impl<L, R> Either<L, R>`[src]

#### `fn is_left(&self) -> bool`[src]

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);```

#### `fn is_right(&self) -> bool`[src]

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);```

#### `fn left(self) -> Option<L>`[src]

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);```

#### `fn right(self) -> Option<R>`[src]

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));```

#### `fn as_ref(&self) -> Either<&L, &R>`[src]

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"));```

#### `fn as_mut(&mut self) -> Either<&mut L, &mut R>`[src]

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));```

#### `fn flip(self) -> Either<R, L>`[src]

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"));```

#### `fn map_left<F, M>(self, f: F) -> Either<M, R> where    F: FnOnce(L) -> M, `[src]

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));```

#### `fn map_right<F, S>(self, f: F) -> Either<L, S> where    F: FnOnce(R) -> S, `[src]

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));```

#### `fn either<F, G, T>(self, f: F, g: G) -> T where    F: FnOnce(L) -> T,    G: FnOnce(R) -> T, `[src]

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);```

#### `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, `[src]

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]);```

#### `fn left_and_then<F, S>(self, f: F) -> Either<S, R> where    F: FnOnce(L) -> Either<S, R>, `[src]

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));```

#### `fn right_and_then<F, S>(self, f: F) -> Either<L, S> where    F: FnOnce(R) -> Either<L, S>, `[src]

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));```

## Trait Implementations

### `impl<L, R> Iterator for Either<L, R> where    L: Iterator,    R: Iterator<Item = <L as Iterator>::Item>, `[src]

`Either<L, R>` is an iterator if both `L` and `R` are iterators.

#### `type Item = <L as Iterator>::Item`

The type of the elements being iterated over.

#### `fn size_hint(&self) -> (usize, Option<usize>)`[src]

Returns the bounds on the remaining length of the iterator. Read more

#### `fn fold<Acc, G>(self, init: Acc, f: G) -> Acc where    G: FnMut(Acc, <Either<L, R> as Iterator>::Item) -> Acc, `[src]

An iterator adaptor that applies a function, producing a single, final value. Read more

#### `fn count(self) -> usize`[src]

Consumes the iterator, counting the number of iterations and returning it. Read more

#### `fn last(self) -> Option<<Either<L, R> as Iterator>::Item>`[src]

Consumes the iterator, returning the last element. Read more

#### `fn nth(&mut self, n: usize) -> Option<<Either<L, R> as Iterator>::Item>`[src]

Returns the `n`th element of the iterator. Read more

#### `fn collect<B>(self) -> B where    B: FromIterator<<Either<L, R> as Iterator>::Item>, `[src]

Transforms an iterator into a collection. Read more

#### `fn all<F>(&mut self, f: F) -> bool where    F: FnMut(<Either<L, R> as Iterator>::Item) -> bool, `[src]

Tests if every element of the iterator matches a predicate. Read more

#### `fn step_by(self, step: usize) -> StepBy<Self>`[src]

🔬 This is a nightly-only experimental API. (`iterator_step_by`)

unstable replacement of Range::step_by

Creates an iterator starting at the same point, but stepping by the given amount at each iteration. Read more

#### `fn chain<U>(self, other: U) -> Chain<Self, <U as IntoIterator>::IntoIter> where    U: IntoIterator<Item = Self::Item>, `1.0.0[src]

Takes two iterators and creates a new iterator over both in sequence. Read more

#### `fn zip<U>(self, other: U) -> Zip<Self, <U as IntoIterator>::IntoIter> where    U: IntoIterator, `1.0.0[src]

'Zips up' two iterators into a single iterator of pairs. Read more

#### `fn map<B, F>(self, f: F) -> Map<Self, F> where    F: FnMut(Self::Item) -> B, `1.0.0[src]

Takes a closure and creates an iterator which calls that closure on each element. Read more

#### `fn for_each<F>(self, f: F) where    F: FnMut(Self::Item) -> (), `1.22.0[src]

Calls a closure on each element of an iterator. Read more

#### `fn filter<P>(self, predicate: P) -> Filter<Self, P> where    P: FnMut(&Self::Item) -> bool, `1.0.0[src]

Creates an iterator which uses a closure to determine if an element should be yielded. Read more

#### `fn filter_map<B, F>(self, f: F) -> FilterMap<Self, F> where    F: FnMut(Self::Item) -> Option<B>, `1.0.0[src]

Creates an iterator that both filters and maps. Read more

#### `fn enumerate(self) -> Enumerate<Self>`1.0.0[src]

Creates an iterator which gives the current iteration count as well as the next value. Read more

#### `fn peekable(self) -> Peekable<Self>`1.0.0[src]

Creates an iterator which can use `peek` to look at the next element of the iterator without consuming it. Read more

#### `fn skip_while<P>(self, predicate: P) -> SkipWhile<Self, P> where    P: FnMut(&Self::Item) -> bool, `1.0.0[src]

Creates an iterator that [`skip`]s elements based on a predicate. Read more

#### `fn take_while<P>(self, predicate: P) -> TakeWhile<Self, P> where    P: FnMut(&Self::Item) -> bool, `1.0.0[src]

Creates an iterator that yields elements based on a predicate. Read more

#### `fn skip(self, n: usize) -> Skip<Self>`1.0.0[src]

Creates an iterator that skips the first `n` elements. Read more

#### `fn take(self, n: usize) -> Take<Self>`1.0.0[src]

Creates an iterator that yields its first `n` elements. Read more

#### `fn scan<St, B, F>(self, initial_state: St, f: F) -> Scan<Self, St, F> where    F: FnMut(&mut St, Self::Item) -> Option<B>, `1.0.0[src]

An iterator adaptor similar to [`fold`] that holds internal state and produces a new iterator. Read more

#### `fn flat_map<U, F>(self, f: F) -> FlatMap<Self, U, F> where    F: FnMut(Self::Item) -> U,    U: IntoIterator, `1.0.0[src]

Creates an iterator that works like map, but flattens nested structure. Read more

#### `fn fuse(self) -> Fuse<Self>`1.0.0[src]

Creates an iterator which ends after the first [`None`]. Read more

#### `fn inspect<F>(self, f: F) -> Inspect<Self, F> where    F: FnMut(&Self::Item) -> (), `1.0.0[src]

Do something with each element of an iterator, passing the value on. Read more

#### `fn by_ref(&mut self) -> &mut Self`1.0.0[src]

Borrows an iterator, rather than consuming it. Read more

#### `fn partition<B, F>(self, f: F) -> (B, B) where    B: Default + Extend<Self::Item>,    F: FnMut(&Self::Item) -> bool, `1.0.0[src]

Consumes an iterator, creating two collections from it. Read more

#### `fn any<F>(&mut self, f: F) -> bool where    F: FnMut(Self::Item) -> bool, `1.0.0[src]

Tests if any element of the iterator matches a predicate. Read more

#### `fn find<P>(&mut self, predicate: P) -> Option<Self::Item> where    P: FnMut(&Self::Item) -> bool, `1.0.0[src]

Searches for an element of an iterator that satisfies a predicate. Read more

#### `fn position<P>(&mut self, predicate: P) -> Option<usize> where    P: FnMut(Self::Item) -> bool, `1.0.0[src]

Searches for an element in an iterator, returning its index. Read more

#### `fn rposition<P>(&mut self, predicate: P) -> Option<usize> where    P: FnMut(Self::Item) -> bool,    Self: ExactSizeIterator + DoubleEndedIterator, `1.0.0[src]

Searches for an element in an iterator from the right, returning its index. Read more

#### `fn max(self) -> Option<Self::Item> where    Self::Item: Ord, `1.0.0[src]

Returns the maximum element of an iterator. Read more

#### `fn min(self) -> Option<Self::Item> where    Self::Item: Ord, `1.0.0[src]

Returns the minimum element of an iterator. Read more

#### `fn max_by_key<B, F>(self, f: F) -> Option<Self::Item> where    B: Ord,    F: FnMut(&Self::Item) -> B, `1.6.0[src]

Returns the element that gives the maximum value from the specified function. Read more

#### `fn max_by<F>(self, compare: F) -> Option<Self::Item> where    F: FnMut(&Self::Item, &Self::Item) -> Ordering, `1.15.0[src]

Returns the element that gives the maximum value with respect to the specified comparison function. Read more

#### `fn min_by_key<B, F>(self, f: F) -> Option<Self::Item> where    B: Ord,    F: FnMut(&Self::Item) -> B, `1.6.0[src]

Returns the element that gives the minimum value from the specified function. Read more

#### `fn min_by<F>(self, compare: F) -> Option<Self::Item> where    F: FnMut(&Self::Item, &Self::Item) -> Ordering, `1.15.0[src]

Returns the element that gives the minimum value with respect to the specified comparison function. Read more

#### `fn rev(self) -> Rev<Self> where    Self: DoubleEndedIterator, `1.0.0[src]

Reverses an iterator's direction. Read more

#### `fn unzip<A, B, FromA, FromB>(self) -> (FromA, FromB) where    FromA: Default + Extend<A>,    FromB: Default + Extend<B>,    Self: Iterator<Item = (A, B)>, `1.0.0[src]

Converts an iterator of pairs into a pair of containers. Read more

#### `fn cloned<'a, T>(self) -> Cloned<Self> where    Self: Iterator<Item = &'a T>,    T: 'a + Clone, `1.0.0[src]

Creates an iterator which [`clone`]s all of its elements. Read more

#### `fn cycle(self) -> Cycle<Self> where    Self: Clone, `1.0.0[src]

Repeats an iterator endlessly. Read more

#### `fn sum<S>(self) -> S where    S: Sum<Self::Item>, `1.11.0[src]

Sums the elements of an iterator. Read more

#### `fn product<P>(self) -> P where    P: Product<Self::Item>, `1.11.0[src]

Iterates over the entire iterator, multiplying all the elements Read more

#### `fn cmp<I>(self, other: I) -> Ordering where    I: IntoIterator<Item = Self::Item>,    Self::Item: Ord, `1.5.0[src]

Lexicographically compares the elements of this `Iterator` with those of another. Read more

#### `fn partial_cmp<I>(self, other: I) -> Option<Ordering> where    I: IntoIterator,    Self::Item: PartialOrd<<I as IntoIterator>::Item>, `1.5.0[src]

Lexicographically compares the elements of this `Iterator` with those of another. Read more

#### `fn eq<I>(self, other: I) -> bool where    I: IntoIterator,    Self::Item: PartialEq<<I as IntoIterator>::Item>, `1.5.0[src]

Determines if the elements of this `Iterator` are equal to those of another. Read more

#### `fn ne<I>(self, other: I) -> bool where    I: IntoIterator,    Self::Item: PartialEq<<I as IntoIterator>::Item>, `1.5.0[src]

Determines if the elements of this `Iterator` are unequal to those of another. Read more

#### `fn lt<I>(self, other: I) -> bool where    I: IntoIterator,    Self::Item: PartialOrd<<I as IntoIterator>::Item>, `1.5.0[src]

Determines if the elements of this `Iterator` are lexicographically less than those of another. Read more

#### `fn le<I>(self, other: I) -> bool where    I: IntoIterator,    Self::Item: PartialOrd<<I as IntoIterator>::Item>, `1.5.0[src]

Determines if the elements of this `Iterator` are lexicographically less or equal to those of another. Read more

#### `fn gt<I>(self, other: I) -> bool where    I: IntoIterator,    Self::Item: PartialOrd<<I as IntoIterator>::Item>, `1.5.0[src]

Determines if the elements of this `Iterator` are lexicographically greater than those of another. Read more

#### `fn ge<I>(self, other: I) -> bool where    I: IntoIterator,    Self::Item: PartialOrd<<I as IntoIterator>::Item>, `1.5.0[src]

Determines if the elements of this `Iterator` are lexicographically greater than or equal to those of another. Read more

### `impl<L, R> PartialOrd<Either<L, R>> for Either<L, R> where    L: PartialOrd<L>,    R: PartialOrd<R>, `[src]

#### `fn partial_cmp(&self, __arg_0: &Either<L, R>) -> Option<Ordering>`[src]

This method returns an ordering between `self` and `other` values if one exists. Read more

#### `fn lt(&self, __arg_0: &Either<L, R>) -> bool`[src]

This method tests less than (for `self` and `other`) and is used by the `<` operator. Read more

#### `fn le(&self, __arg_0: &Either<L, R>) -> bool`[src]

This method tests less than or equal to (for `self` and `other`) and is used by the `<=` operator. Read more

#### `fn gt(&self, __arg_0: &Either<L, R>) -> bool`[src]

This method tests greater than (for `self` and `other`) and is used by the `>` operator. Read more

#### `fn ge(&self, __arg_0: &Either<L, R>) -> bool`[src]

This method tests greater than or equal to (for `self` and `other`) and is used by the `>=` operator. Read more

### `impl<L, R> DoubleEndedIterator for Either<L, R> where    L: DoubleEndedIterator,    R: DoubleEndedIterator<Item = <L as Iterator>::Item>, `[src]

#### `fn next_back(&mut self) -> Option<<Either<L, R> as Iterator>::Item>`[src]

Removes and returns an element from the end of the iterator. Read more

#### `fn rfind<P>(&mut self, predicate: P) -> Option<Self::Item> where    P: FnMut(&Self::Item) -> bool, `[src]

🔬 This is a nightly-only experimental API. (`iter_rfind`)

Searches for an element of an iterator from the right that satisfies a predicate. Read more

### `impl<L, R> Debug for Either<L, R> where    L: Debug,    R: Debug, `[src]

#### `fn fmt(&self, __arg_0: &mut Formatter) -> Result<(), Error>`[src]

Formats the value using the given formatter.

### `impl<L, R> PartialEq<Either<L, R>> for Either<L, R> where    L: PartialEq<L>,    R: PartialEq<R>, `[src]

#### `fn eq(&self, __arg_0: &Either<L, R>) -> bool`[src]

This method tests for `self` and `other` values to be equal, and is used by `==`. Read more

#### `fn ne(&self, __arg_0: &Either<L, R>) -> bool`[src]

This method tests for `!=`.

### `impl<L, R> Into<Result<R, L>> for Either<L, R>`[src]

Convert from `Either` to `Result` with `Right => Ok` and `Left => Err`.

### `impl<L, R, A> Extend<A> for Either<L, R> where    L: Extend<A>,    R: Extend<A>, `[src]

#### `fn extend<T>(&mut self, iter: T) where    T: IntoIterator<Item = A>, `[src]

Extends a collection with the contents of an iterator. Read more

### `impl<L, R> ExactSizeIterator for Either<L, R> where    L: ExactSizeIterator,    R: ExactSizeIterator<Item = <L as Iterator>::Item>, `[src]

#### `fn len(&self) -> usize`1.0.0[src]

Returns the exact number of times the iterator will iterate. Read more

#### `fn is_empty(&self) -> bool`[src]

🔬 This is a nightly-only experimental API. (`exact_size_is_empty`)

Returns whether the iterator is empty. Read more

### `impl<L, R> Clone for Either<L, R> where    L: Clone,    R: Clone, `[src]

#### `fn clone(&self) -> Either<L, R>`[src]

Returns a copy of the value. Read more

#### `fn clone_from(&mut self, source: &Self)`1.0.0[src]

Performs copy-assignment from `source`. Read more

### `impl<L, R, Target> AsMut<Target> for Either<L, R> where    L: AsMut<Target>,    R: AsMut<Target>, `[src]

#### `fn as_mut(&mut self) -> &mut Target`[src]

Performs the conversion.

### `impl<L, R> Hash for Either<L, R> where    L: Hash,    R: Hash, `[src]

#### `fn hash<__HLR>(&self, __arg_0: &mut __HLR) where    __HLR: Hasher, `[src]

Feeds this value into the given [`Hasher`]. Read more

#### `fn hash_slice<H>(data: &[Self], state: &mut H) where    H: Hasher, `1.3.0[src]

Feeds a slice of this type into the given [`Hasher`]. Read more

### `impl<L, R, Target> AsRef<Target> for Either<L, R> where    L: AsRef<Target>,    R: AsRef<Target>, `[src]

#### `fn as_ref(&self) -> &Target`[src]

Performs the conversion.

### `impl<L, R> Ord for Either<L, R> where    L: Ord,    R: Ord, `[src]

#### `fn cmp(&self, __arg_0: &Either<L, R>) -> Ordering`[src]

This method returns an `Ordering` between `self` and `other`. Read more

#### `fn max(self, other: Self) -> Self`1.22.0[src]

Compares and returns the maximum of two values. Read more

#### `fn min(self, other: Self) -> Self`1.22.0[src]

Compares and returns the minimum of two values. Read more

### `impl<L, R> From<Result<R, L>> for Either<L, R>`[src]

Convert from `Result` to `Either` with `Ok => Right` and `Err => Left`.

#### `fn from(r: Result<R, L>) -> Either<L, R>`[src]

Performs the conversion.

### `impl<L, R> Display for Either<L, R> where    L: Display,    R: Display, `[src]

#### `fn fmt(&self, f: &mut Formatter) -> Result<(), Error>`[src]

Formats the value using the given formatter. Read more