[][src]Enum either::Either

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

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.)

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));

Important traits for Either<L, 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"));

Important traits for Either<L, R>

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));

Important traits for Either<L, R>

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"));

Important traits for Either<L, 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));

Important traits for Either<L, 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));

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);

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]);

Important traits for Either<L, 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));

Important traits for Either<L, 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));

Important traits for Either<L, 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]));

impl<T, L, R> Either<(T, L), (T, R)>
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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);

impl<T, L, R> Either<(L, T), (R, T)>
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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);

impl<T> Either<T, T>
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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);

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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Important traits for Either<L, R>

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

Compares and returns the maximum of two values. Read more

Compares and returns the minimum of two values. 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. Read more

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 method 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

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

Calls a closure on each element of an iterator. 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 that 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

An iterator method that applies a function as long as it returns successfully, producing a single, final value. Read more

An iterator method that applies a fallible function to each item in the iterator, stopping at the first error and returning that error. 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

Applies function to the elements of iterator and returns the first non-none result. 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 the reverse version of [try_fold()]: it takes elements starting from the back of the iterator. Read more

An iterator method that reduces the iterator's elements to a single, final value, starting from the back. Read more

Searches for an element of an iterator from the back 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

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

Determines if this Reader can work with buffers of uninitialized memory. Read more

Read all bytes until EOF in this source, appending them to 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

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.

Dereferences the value.

impl<L, R> DerefMut for Either<L, R> where
    L: DerefMut,
    R: DerefMut<Target = L::Target>, 
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Mutably dereferences the 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.

This method is soft-deprecated. 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

Auto Trait Implementations

impl<L, R> Send for Either<L, R> where
    L: Send,
    R: Send

impl<L, R> Sync for Either<L, R> where
    L: Sync,
    R: Sync

Blanket Implementations

impl<T> From for T
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Performs the conversion.

impl<I> IntoIterator for I where
    I: Iterator
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The type of the elements being iterated over.

Which kind of iterator are we turning this into?

Creates an iterator from a value. Read more

impl<T, U> Into for T where
    U: From<T>, 
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Performs the conversion.

impl<T> ToOwned for T where
    T: Clone
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Creates owned data from borrowed data, usually by cloning. Read more

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

recently added

Uses borrowed data to replace owned data, usually by cloning. Read more

impl<T> ToString for T where
    T: Display + ?Sized
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Converts the given value to a String. Read more

impl<T, U> TryFrom for T where
    T: From<U>, 
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🔬 This is a nightly-only experimental API. (try_from)

The type returned in the event of a conversion error.

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

Performs the conversion.

impl<T> Borrow for T where
    T: ?Sized
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Immutably borrows from an owned value. Read more

impl<T> Any for T where
    T: 'static + ?Sized
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🔬 This is a nightly-only experimental API. (get_type_id)

this method will likely be replaced by an associated static

Gets the TypeId of self. Read more

impl<T, U> TryInto for T where
    U: TryFrom<T>, 
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🔬 This is a nightly-only experimental API. (try_from)

The type returned in the event of a conversion error.

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

Performs the conversion.

impl<T> BorrowMut for T where
    T: ?Sized
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Mutably borrows from an owned value. Read more