Enum either::Either [−][src]
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 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);
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,
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,
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);
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
Performs the conversion.
impl<L, R> DoubleEndedIterator for Either<L, R> where
L: DoubleEndedIterator,
R: DoubleEndedIterator<Item = L::Item>,
impl<L, R> DoubleEndedIterator for Either<L, R> where
L: DoubleEndedIterator,
R: DoubleEndedIterator<Item = L::Item>,
Removes and returns an element from the end of the iterator. Read more
iter_advance_by
)Advances the iterator from the back by n
elements. Read more
Returns the n
th 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
An iterator method that reduces the iterator’s elements to a single, final value, starting from the back. Read more
impl<L, R> ExactSizeIterator for Either<L, R> where
L: ExactSizeIterator,
R: ExactSizeIterator<Item = L::Item>,
impl<L, R> ExactSizeIterator for Either<L, R> where
L: ExactSizeIterator,
R: ExactSizeIterator<Item = L::Item>,
Extends a collection with the contents of an iterator. Read more
extend_one
)Extends a collection with exactly one element.
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
.
Convert from Either
to Result
with Right => Ok
and Left => Err
.
Either<L, R>
is an iterator if both L
and R
are iterators.
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
Consumes the iterator, counting the number of iterations and returning it. Read more
Consumes the iterator, returning the last element. Read more
Returns the n
th 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
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
1.0.0[src]fn chain<U>(self, other: U) -> Chain<Self, <U as IntoIterator>::IntoIter> where
U: IntoIterator<Item = Self::Item>,
fn chain<U>(self, other: U) -> Chain<Self, <U as IntoIterator>::IntoIter> where
U: IntoIterator<Item = Self::Item>,
Takes two iterators and creates a new iterator over both in sequence. Read more
1.0.0[src]fn zip<U>(self, other: U) -> Zip<Self, <U as IntoIterator>::IntoIter> where
U: IntoIterator,
fn zip<U>(self, other: U) -> Zip<Self, <U as IntoIterator>::IntoIter> where
U: IntoIterator,
‘Zips up’ two iterators into a single iterator of pairs. Read more
iter_intersperse
)Creates a new iterator which places a copy of separator
between adjacent
items of the original iterator. Read more
fn intersperse_with<G>(self, separator: G) -> IntersperseWith<Self, G> where
G: FnMut() -> Self::Item,
fn intersperse_with<G>(self, separator: G) -> IntersperseWith<Self, G> where
G: FnMut() -> Self::Item,
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
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 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
Creates an iterator that works like map, but flattens nested structure. Read more
Creates an iterator that flattens nested structure. Read more
Does something with each element of an iterator, passing the value on. Read more
Consumes an iterator, creating two collections from it. Read more
fn partition_in_place<'a, T, P>(self, predicate: P) -> usize where
T: 'a,
Self: DoubleEndedIterator<Item = &'a mut T>,
P: FnMut(&T) -> bool,
fn partition_in_place<'a, T, P>(self, predicate: P) -> usize where
T: 'a,
Self: DoubleEndedIterator<Item = &'a mut T>,
P: FnMut(&T) -> bool,
iter_partition_in_place
)Reorders the elements of this iterator in-place according to the given predicate,
such that all those that return true
precede all those that return false
.
Returns the number of true
elements found. Read more
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
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
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
try_find
)Applies function to the elements of iterator and returns the first true result or the first error. Read more
Searches for an element in an iterator, returning its index. Read more
1.0.0[src]fn rposition<P>(&mut self, predicate: P) -> Option<usize> where
P: FnMut(Self::Item) -> bool,
Self: ExactSizeIterator + DoubleEndedIterator,
fn rposition<P>(&mut self, predicate: P) -> Option<usize> where
P: FnMut(Self::Item) -> bool,
Self: ExactSizeIterator + DoubleEndedIterator,
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 copies all of its elements. 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
fn cmp_by<I, F>(self, other: I, cmp: F) -> Ordering where
I: IntoIterator,
F: FnMut(Self::Item, <I as IntoIterator>::Item) -> Ordering,
fn cmp_by<I, F>(self, other: I, cmp: F) -> Ordering where
I: IntoIterator,
F: FnMut(Self::Item, <I as IntoIterator>::Item) -> Ordering,
iter_order_by
)Lexicographically compares the elements of this Iterator
with those
of another with respect to the specified comparison function. Read more
1.5.0[src]fn partial_cmp<I>(self, other: I) -> Option<Ordering> where
I: IntoIterator,
Self::Item: PartialOrd<<I as IntoIterator>::Item>,
fn partial_cmp<I>(self, other: I) -> Option<Ordering> where
I: IntoIterator,
Self::Item: PartialOrd<<I as IntoIterator>::Item>,
Lexicographically compares the elements of this Iterator
with those
of another. Read more
fn partial_cmp_by<I, F>(self, other: I, partial_cmp: F) -> Option<Ordering> where
I: IntoIterator,
F: FnMut(Self::Item, <I as IntoIterator>::Item) -> Option<Ordering>,
fn partial_cmp_by<I, F>(self, other: I, partial_cmp: F) -> Option<Ordering> where
I: IntoIterator,
F: FnMut(Self::Item, <I as IntoIterator>::Item) -> Option<Ordering>,
iter_order_by
)Lexicographically compares the elements of this Iterator
with those
of another with respect to the specified comparison function. Read more
1.5.0[src]fn eq<I>(self, other: I) -> bool where
I: IntoIterator,
Self::Item: PartialEq<<I as IntoIterator>::Item>,
fn eq<I>(self, other: I) -> bool where
I: IntoIterator,
Self::Item: PartialEq<<I as IntoIterator>::Item>,
fn eq_by<I, F>(self, other: I, eq: F) -> bool where
I: IntoIterator,
F: FnMut(Self::Item, <I as IntoIterator>::Item) -> bool,
fn eq_by<I, F>(self, other: I, eq: F) -> bool where
I: IntoIterator,
F: FnMut(Self::Item, <I as IntoIterator>::Item) -> bool,
iter_order_by
)1.5.0[src]fn ne<I>(self, other: I) -> bool where
I: IntoIterator,
Self::Item: PartialEq<<I as IntoIterator>::Item>,
fn ne<I>(self, other: I) -> bool where
I: IntoIterator,
Self::Item: PartialEq<<I as IntoIterator>::Item>,
1.5.0[src]fn lt<I>(self, other: I) -> bool where
I: IntoIterator,
Self::Item: PartialOrd<<I as IntoIterator>::Item>,
fn lt<I>(self, other: I) -> bool where
I: IntoIterator,
Self::Item: PartialOrd<<I as IntoIterator>::Item>,
Determines if the elements of this Iterator
are lexicographically
less than those of another. Read more
1.5.0[src]fn le<I>(self, other: I) -> bool where
I: IntoIterator,
Self::Item: PartialOrd<<I as IntoIterator>::Item>,
fn le<I>(self, other: I) -> bool where
I: IntoIterator,
Self::Item: PartialOrd<<I as IntoIterator>::Item>,
Determines if the elements of this Iterator
are lexicographically
less or equal to those of another. Read more
1.5.0[src]fn gt<I>(self, other: I) -> bool where
I: IntoIterator,
Self::Item: PartialOrd<<I as IntoIterator>::Item>,
fn gt<I>(self, other: I) -> bool where
I: IntoIterator,
Self::Item: PartialOrd<<I as IntoIterator>::Item>,
Determines if the elements of this Iterator
are lexicographically
greater than those of another. Read more
1.5.0[src]fn ge<I>(self, other: I) -> bool where
I: IntoIterator,
Self::Item: PartialOrd<<I as IntoIterator>::Item>,
fn ge<I>(self, other: I) -> bool where
I: IntoIterator,
Self::Item: PartialOrd<<I as IntoIterator>::Item>,
Determines if the elements of this Iterator
are lexicographically
greater than or equal to those of another. Read more
is_sorted
)Checks if the elements of this iterator are sorted. Read more
is_sorted
)Checks if the elements of this iterator are sorted using the given comparator function. Read more
fn is_sorted_by_key<F, K>(self, f: F) -> bool where
F: FnMut(Self::Item) -> K,
K: PartialOrd<K>,
fn is_sorted_by_key<F, K>(self, f: F) -> bool where
F: FnMut(Self::Item) -> K,
K: PartialOrd<K>,
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
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