Enum itertools::Either

source · [−]
pub enum Either<L, R> {
    Left(L),
    Right(R),
}
Expand description

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

Left(L)

A value of type L.

Right(R)

A value of type R.

Implementations

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 Pin<&Either<L, R>> to Either<Pin<&L>, Pin<&R>>, pinned projections of the inner variants.

Convert Pin<&mut Either<L, R>> to Either<Pin<&mut L>, Pin<&mut R>>, pinned projections of the inner variants.

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);

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]);

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));

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]));

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.

Examples
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");

Return left or a default

Examples
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());

Returns left value or computes it from a closure

Examples
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");

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.

Examples
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");

Return right or a default

Examples
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);

Returns right value or computes it from a closure

Examples
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);

Returns the left value

Examples
let left: Either<_, ()> = Left(3);
assert_eq!(left.unwrap_left(), 3);
Panics

When Either is a Right value

ⓘ
let right: Either<(), _> = Right(3);
right.unwrap_left();

Returns the right value

Examples
let right: Either<(), _> = Right(3);
assert_eq!(right.unwrap_right(), 3);
Panics

When Either is a Left value

ⓘ
let left: Either<_, ()> = Left(3);
left.unwrap_right();

Returns the left value

Examples
let left: Either<_, ()> = Left(3);
assert_eq!(left.expect_left("value was Right"), 3);
Panics

When Either is a Right value

ⓘ
let right: Either<(), _> = Right(3);
right.expect_left("value was Right");

Returns the right value

Examples
let right: Either<(), _> = Right(3);
assert_eq!(right.expect_right("value was Left"), 3);
Panics

When Either is a Left value

ⓘ
let left: Either<_, ()> = Left(3);
left.expect_right("value was Right");

Convert the contained value into T

Examples
// 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);

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())));

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())));

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())));

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);

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);

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);

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));

Trait Implementations

Converts this type into a mutable reference of the (usually inferred) input type.
Converts this type into a mutable reference of the (usually inferred) input type.
Converts this type into a mutable reference of the (usually inferred) input type.
Converts this type into a shared reference of the (usually inferred) input type.
Converts this type into a shared reference of the (usually inferred) input type.
Converts this type into a shared reference of the (usually inferred) input type.
Returns a copy of the value. Read more
Performs copy-assignment from source. Read more
Formats the value using the given formatter. Read more
The resulting type after dereferencing.
Dereferences the value.
Mutably dereferences the value.
Formats the value using the given formatter. Read more
Removes and returns an element from the end 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
🔬This is a nightly-only experimental API. (iter_advance_by)
Advances the iterator from the back by n elements. Read more
Returns the nth element from the end of the iterator. Read more
This is the reverse version of Iterator::try_fold(): it takes elements starting from the back of the iterator. Read more
Returns the exact remaining length of the iterator. Read more
🔬This is a nightly-only experimental API. (exact_size_is_empty)
Returns true if the iterator is empty. Read more
Extends a collection with the contents of an iterator. Read more
🔬This is a nightly-only experimental API. (extend_one)
Extends a collection with exactly one element.
🔬This is a nightly-only experimental API. (extend_one)
Reserves capacity in a collection for the given number of additional elements. Read more

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

Converts to this type from the input type.

Either<L, R> is a future if both L and R are futures.

The type of value produced on completion.
Attempt to resolve the future to a final value, registering the current task for wakeup if the value is not yet available. Read more
Feeds this value into the given Hasher. Read more
Feeds a slice of this type into the given Hasher. Read more

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

Converts this type into the (usually inferred) input type.

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
Folds every element into an accumulator by applying an operation, returning the final result. Read more
Calls a closure on each element of an iterator. 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
Consumes an iterator, creating two collections from it. Read more
Tests if every element of the iterator matches a predicate. 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
🔬This is a nightly-only experimental API. (iter_next_chunk)
Advances the iterator and returns an array containing the next N values. Read more
🔬This is a nightly-only experimental API. (iter_advance_by)
Advances the iterator by n elements. 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
🔬This is a nightly-only experimental API. (iter_intersperse)
Creates a new iterator which places an item generated by separator between adjacent items of the original iterator. 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 the peek and peek_mut methods to look at the next element of the iterator without consuming it. See their documentation for more information. Read more
Creates an iterator that skips elements based on a predicate. Read more
Creates an iterator that yields elements based on a predicate. Read more
Creates an iterator that both yields elements based on a predicate and maps. Read more
Creates an iterator that skips the first n elements. Read more
Creates an iterator that yields the first n elements, or fewer if the underlying iterator ends sooner. Read more
An iterator adapter 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
Does something with each element of an iterator, passing the value on. Read more
Borrows an iterator, rather than consuming it. Read more
🔬This is a nightly-only experimental API. (iter_collect_into)
Collects all the items from an iterator into a collection. Read more
🔬This is a nightly-only experimental API. (iter_is_partitioned)
Checks if the elements of this iterator are partitioned according to the given predicate, such that all those that return true precede all those that return false. 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
Reduces the elements to a single one, by repeatedly applying a reducing operation. Read more
🔬This is a nightly-only experimental API. (iterator_try_reduce)
Reduces the elements to a single one by repeatedly applying a reducing operation. If the closure returns a failure, the failure is propagated back to the caller immediately. Read more
🔬This is a nightly-only experimental API. (try_find)
Applies function to the elements of iterator and returns the first true result or the first error. 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
Converts an iterator of pairs into a pair of containers. Read more
Creates an iterator which copies all of its elements. Read more
Creates an iterator which clones all of its elements. Read more
🔬This is a nightly-only experimental API. (iter_array_chunks)
Returns an iterator over N elements of the iterator at a time. Read more
Sums the elements of an iterator. Read more
Iterates over the entire iterator, multiplying all the elements Read more
🔬This is a nightly-only experimental API. (iter_order_by)
Lexicographically compares the elements of this Iterator with those of another with respect to the specified comparison function. Read more
Lexicographically compares the elements of this Iterator with those of another. Read more
🔬This is a nightly-only experimental API. (iter_order_by)
Lexicographically compares the elements of this Iterator with those of another with respect to the specified comparison function. Read more
Determines if the elements of this Iterator are equal to those of another. Read more
🔬This is a nightly-only experimental API. (iter_order_by)
Determines if the elements of this Iterator are equal to those of another with respect to the specified equality function. 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
🔬This is a nightly-only experimental API. (is_sorted)
Checks if the elements of this iterator are sorted using the given comparator function. Read more
🔬This is a nightly-only experimental API. (is_sorted)
Checks if the elements of this iterator are sorted using the given key extraction function. Read more
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
Restrict a value to a certain interval. Read more
This method tests for self and other values to be equal, and is used by ==. Read more
This method tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason. Read more
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

Auto Trait Implementations

Blanket Implementations

Gets the TypeId of self. Read more
Immutably borrows from an owned value. Read more
Mutably borrows from an owned value. Read more

Returns the argument unchanged.

Calls U::from(self).

That is, this conversion is whatever the implementation of From<T> for U chooses to do.

The output that the future will produce on completion.
Which kind of future are we turning this into?
Creates a future from a value. Read more
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
Alternate elements from two iterators until both have run out. Read more
Alternate elements from two iterators until at least one of them has run out. Read more
An iterator adaptor to insert a particular value between each element of the adapted iterator. Read more
Create an iterator which iterates over both this and the specified iterator simultaneously, yielding pairs of two optional elements. Read more
Create an iterator which iterates over both this and the specified iterator simultaneously, yielding pairs of elements. Read more
A “meta iterator adaptor”. Its closure receives a reference to the iterator and may pick off as many elements as it likes, to produce the next iterator element. Read more
Return an iterator over all contiguous windows producing tuples of a specific size (up to 4). Read more
Return an iterator that groups the items in tuples of a specific size (up to 4). Read more
👎Deprecated since 0.8: Use std .step_by() instead
Return an iterator adaptor that steps n elements in the base iterator for each iteration. Read more
Convert each item of the iterator using the Into trait. Read more
Return an iterator adaptor that applies the provided closure to every Result::Ok value. Result::Err values are unchanged. Read more
Return an iterator adaptor that merges the two base iterators in ascending order. If both base iterators are sorted (ascending), the result is sorted. Read more
Return an iterator adaptor that merges the two base iterators in order. This is much like .merge() but allows for a custom ordering. Read more
Create an iterator that merges items from both this and the specified iterator in ascending order. Read more
Return an iterator adaptor that iterates over the cartesian product of the element sets of two iterators self and J. Read more
Return an iterator adaptor that uses the passed-in closure to optionally merge together consecutive elements. Read more
Remove duplicates from sections of consecutive identical elements. If the iterator is sorted, all elements will be unique. Read more
Remove duplicates from sections of consecutive identical elements, determining equality using a comparison function. If the iterator is sorted, all elements will be unique. Read more
Return an iterator adaptor that borrows from this iterator and takes items while the closure accept returns true. Read more
Return an iterator adaptor that borrows from a Clone-able iterator to only pick off elements while the predicate accept returns true. Read more
Return an iterator adaptor that filters Option<A> iterator elements and produces A. Stops on the first None encountered. Read more
Return an iterator adaptor that iterates over the combinations of the elements from an iterator. Read more
Return an iterator adaptor that pads the sequence to a minimum length of min by filling missing elements using a closure f. Read more
Return an iterator adaptor that wraps each element in a Position to ease special-case handling of the first or last elements. Read more
Return an iterator adaptor that yields the indices of all elements satisfying a predicate, counted from the start of the iterator. Read more
Return an iterator adaptor that applies a mutating function to each element before yielding it. Read more
Advances the iterator and returns the next items grouped in a tuple of a specific size (up to 4). Read more
Collects all items from the iterator into a tuple of a specific size (up to 4). Read more
Find the position and value of the first element satisfying a predicate. Read more
Check whether all elements compare equal. Read more
Consume the first n elements from the iterator eagerly, and return the same iterator again. Read more
Consume the last n elements from the iterator eagerly, and return the same iterator again. Read more
👎Deprecated since 0.8: Use .for_each() instead
Run the closure f eagerly on each element of the iterator. Read more
Combine all an iterator’s elements into one element by using Extend. Read more
Assign to each reference in self from the from iterator, stopping at the shortest of the two iterators. Read more
Format all iterator elements, separated by sep. Read more
Format all iterator elements, separated by sep. Read more
Fold Result values from an iterator. Read more
Fold Option values from an iterator. Read more
Accumulator of the elements in the iterator. Read more
Accumulate the elements in the iterator in a tree-like manner. Read more
👎Deprecated since 0.8: Use .try_fold() instead
An iterator method that applies a function, producing a single, final value. Read more
Iterate over the entire iterator and add all the elements. Read more
Iterate over the entire iterator and multiply all the elements. Read more
Collect all iterator elements into one of two partitions. Unlike Iterator::partition, each partition may have a distinct type. Read more
Return the minimum and maximum elements in the iterator. Read more
Return the minimum and maximum element of an iterator, as determined by the specified function. Read more
Return the minimum and maximum element of an iterator, as determined by the specified comparison function. Read more
If the iterator yields exactly one element, that element will be returned, otherwise an error will be returned containing an iterator that has the same output as the input iterator. Read more
The type returned in the event of a conversion error.
Performs the conversion.
The type returned in the event of a conversion error.
Performs the conversion.