Enum either::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>
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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);

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);

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);

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));

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"));

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));

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"));

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));

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));

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);

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));

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: Copy, R: Copy> Copy for Either<L, R>
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impl<L: Clone, R: Clone> Clone for Either<L, R>
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Returns a copy of the value. Read more

Performs copy-assignment from source. Read more

impl<L: PartialEq, R: PartialEq> PartialEq for Either<L, R>
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This method tests for self and other values to be equal, and is used by ==. Read more

This method tests for !=.

impl<L: Eq, R: Eq> Eq for Either<L, R>
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impl<L: PartialOrd, R: PartialOrd> PartialOrd for Either<L, R>
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This method returns an ordering between self and other values if one exists. Read more

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

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

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

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

impl<L: Ord, R: Ord> Ord for Either<L, R>
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This method returns an Ordering between self and other. Read more

impl<L: Hash, R: Hash> Hash for Either<L, R>
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Feeds this value into the given [Hasher]. Read more

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

impl<L: Debug, R: Debug> Debug for Either<L, R>
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Formats the value using the given formatter.

impl<L, R> From<Result<R, L>> for Either<L, R>
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Convert from Result to Either with Ok => Right and Err => Left.

Performs the conversion.

impl<L, R> Into<Result<R, L>> for Either<L, R>
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Convert from Either to Result with Right => Ok and Left => Err.

Performs the conversion.

impl<L, R, A> Extend<A> for Either<L, R> where
    L: Extend<A>,
    R: Extend<A>, 
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Extends a collection with the contents of an iterator. Read more

impl<L, R> Iterator for Either<L, R> where
    L: Iterator,
    R: Iterator<Item = L::Item>, 
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Either<L, R> is an iterator if both L and R are iterators.

The type of the elements being iterated over.

Advances the iterator and returns the next value. Read more

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

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

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

Consumes the iterator, returning the last element. Read more

Returns the nth element of the iterator. Read more

Transforms an iterator into a collection. Read more

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

🔬 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

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

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

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

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

Creates an iterator that both filters and maps. Read more

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

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

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

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

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

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

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

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

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

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

Borrows an iterator, rather than consuming it. Read more

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

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

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

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

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

Returns the maximum element of an iterator. Read more

Returns the minimum element of an iterator. Read more

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

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

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

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

Reverses an iterator's direction. Read more

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

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

Repeats an iterator endlessly. Read more

Sums the elements of an iterator. Read more

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

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

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

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

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

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

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

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

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

impl<L, R> DoubleEndedIterator for Either<L, R> where
    L: DoubleEndedIterator,
    R: DoubleEndedIterator<Item = L::Item>, 
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Removes and returns an element from the end of the iterator. Read more

🔬 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> ExactSizeIterator for Either<L, R> where
    L: ExactSizeIterator,
    R: ExactSizeIterator<Item = L::Item>, 
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Returns the exact number of times the iterator will iterate. Read more

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

Returns whether the iterator is empty. Read more

impl<L, R> Read for Either<L, R> where
    L: Read,
    R: Read
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Either<L, R> implements Read if both L and R do.

Requires crate feature "use_std"

Pull some bytes from this source into the specified buffer, returning how many bytes were read. Read more

Read all bytes until EOF in this source, placing them into buf. Read more

Read all bytes until EOF in this source, placing them into buf. Read more

Read the exact number of bytes required to fill buf. Read more

Creates a "by reference" adaptor for this instance of Read. Read more

Transforms this Read instance to an Iterator over its bytes. Read more

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

the semantics of a partial read/write of where errors happen is currently unclear and may change

Transforms this Read instance to an Iterator over chars. Read more

Creates an adaptor which will chain this stream with another. Read more

Creates an adaptor which will read at most limit bytes from it. Read more

impl<L, R> BufRead for Either<L, R> where
    L: BufRead,
    R: BufRead
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Requires crate feature "use_std"

Fills the internal buffer of this object, returning the buffer contents. Read more

Tells this buffer that amt bytes have been consumed from the buffer, so they should no longer be returned in calls to read. Read more

Read all bytes into buf until the delimiter byte or EOF is reached. Read more

Read all bytes until a newline (the 0xA byte) is reached, and append them to the provided buffer. Read more

Returns an iterator over the contents of this reader split on the byte byte. Read more

Returns an iterator over the lines of this reader. Read more

impl<L, R> Write for Either<L, R> where
    L: Write,
    R: Write
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Either<L, R> implements Write if both L and R do.

Requires crate feature "use_std"

Write a buffer into this object, returning how many bytes were written. Read more

Flush this output stream, ensuring that all intermediately buffered contents reach their destination. Read more

Attempts to write an entire buffer into this write. Read more

Writes a formatted string into this writer, returning any error encountered. Read more

Creates a "by reference" adaptor for this instance of Write. Read more

impl<L, R, Target> AsRef<Target> for Either<L, R> where
    L: AsRef<Target>,
    R: AsRef<Target>, 
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Performs the conversion.

impl<L, R, Target> AsMut<Target> for Either<L, R> where
    L: AsMut<Target>,
    R: AsMut<Target>, 
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Performs the conversion.

impl<L, R> Deref for Either<L, R> where
    L: Deref,
    R: Deref<Target = L::Target>, 
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The resulting type after dereferencing

The method called to dereference a value

impl<L, R> DerefMut for Either<L, R> where
    L: DerefMut,
    R: DerefMut<Target = L::Target>, 
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The method called to mutably dereference a value

impl<L, R> Error for Either<L, R> where
    L: Error,
    R: Error
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Either implements Error if both L and R implement it.

A short description of the error. Read more

The lower-level cause of this error, if any. Read more

impl<L, R> Display for Either<L, R> where
    L: Display,
    R: Display
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Formats the value using the given formatter. Read more