[−][src]Trait rayon::iter::ParallelIterator

pub trait ParallelIterator: Sized + Send {
    type Item: Send;
    fn drive_unindexed<C>(self, consumer: C) -> C::Result
    where
        C: UnindexedConsumer<Self::Item>;

    fn for_each<OP>(self, op: OP)
    where
        OP: Fn(Self::Item) + Sync + Send,
    { ... }

    fn for_each_with<OP, T>(self, init: T, op: OP)
    where
        OP: Fn(&mut T, Self::Item) + Sync + Send,
        T: Send + Clone,
    { ... }

    fn for_each_init<OP, INIT, T>(self, init: INIT, op: OP)
    where
        OP: Fn(&mut T, Self::Item) + Sync + Send,
        INIT: Fn() -> T + Sync + Send,
    { ... }

    fn try_for_each<OP, R>(self, op: OP) -> R
    where
        OP: Fn(Self::Item) -> R + Sync + Send,
        R: Try<Ok = ()> + Send,
    { ... }

    fn try_for_each_with<OP, T, R>(self, init: T, op: OP) -> R
    where
        OP: Fn(&mut T, Self::Item) -> R + Sync + Send,
        T: Send + Clone,
        R: Try<Ok = ()> + Send,
    { ... }

    fn try_for_each_init<OP, INIT, T, R>(self, init: INIT, op: OP) -> R
    where
        OP: Fn(&mut T, Self::Item) -> R + Sync + Send,
        INIT: Fn() -> T + Sync + Send,
        R: Try<Ok = ()> + Send,
    { ... }

    fn count(self) -> usize { ... }

    fn map<F, R>(self, map_op: F) -> Map<Self, F>
    where
        F: Fn(Self::Item) -> R + Sync + Send,
        R: Send,
    { ... }

    fn map_with<F, T, R>(self, init: T, map_op: F) -> MapWith<Self, T, F>
    where
        F: Fn(&mut T, Self::Item) -> R + Sync + Send,
        T: Send + Clone,
        R: Send,
    { ... }

    fn map_init<F, INIT, T, R>(
        self, 
        init: INIT, 
        map_op: F
    ) -> MapInit<Self, INIT, F>
    where
        F: Fn(&mut T, Self::Item) -> R + Sync + Send,
        INIT: Fn() -> T + Sync + Send,
        R: Send,
    { ... }

    fn cloned<'a, T>(self) -> Cloned<Self>
    where
        T: 'a + Clone + Send,
        Self: ParallelIterator<Item = &'a T>,
    { ... }

    fn copied<'a, T>(self) -> Copied<Self>
    where
        T: 'a + Copy + Send,
        Self: ParallelIterator<Item = &'a T>,
    { ... }

    fn inspect<OP>(self, inspect_op: OP) -> Inspect<Self, OP>
    where
        OP: Fn(&Self::Item) + Sync + Send,
    { ... }

    fn update<F>(self, update_op: F) -> Update<Self, F>
    where
        F: Fn(&mut Self::Item) + Sync + Send,
    { ... }

    fn filter<P>(self, filter_op: P) -> Filter<Self, P>
    where
        P: Fn(&Self::Item) -> bool + Sync + Send,
    { ... }

    fn filter_map<P, R>(self, filter_op: P) -> FilterMap<Self, P>
    where
        P: Fn(Self::Item) -> Option<R> + Sync + Send,
        R: Send,
    { ... }

    fn flat_map<F, PI>(self, map_op: F) -> FlatMap<Self, F>
    where
        F: Fn(Self::Item) -> PI + Sync + Send,
        PI: IntoParallelIterator,
    { ... }

    fn flatten(self) -> Flatten<Self>
    where
        Self::Item: IntoParallelIterator,
    { ... }

    fn reduce<OP, ID>(self, identity: ID, op: OP) -> Self::Item
    where
        OP: Fn(Self::Item, Self::Item) -> Self::Item + Sync + Send,
        ID: Fn() -> Self::Item + Sync + Send,
    { ... }

    fn reduce_with<OP>(self, op: OP) -> Option<Self::Item>
    where
        OP: Fn(Self::Item, Self::Item) -> Self::Item + Sync + Send,
    { ... }

    fn try_reduce<T, OP, ID>(self, identity: ID, op: OP) -> Self::Item
    where
        OP: Fn(T, T) -> Self::Item + Sync + Send,
        ID: Fn() -> T + Sync + Send,
        Self::Item: Try<Ok = T>,
    { ... }

    fn try_reduce_with<T, OP>(self, op: OP) -> Option<Self::Item>
    where
        OP: Fn(T, T) -> Self::Item + Sync + Send,
        Self::Item: Try<Ok = T>,
    { ... }

    fn fold<T, ID, F>(self, identity: ID, fold_op: F) -> Fold<Self, ID, F>
    where
        F: Fn(T, Self::Item) -> T + Sync + Send,
        ID: Fn() -> T + Sync + Send,
        T: Send,
    { ... }

    fn fold_with<F, T>(self, init: T, fold_op: F) -> FoldWith<Self, T, F>
    where
        F: Fn(T, Self::Item) -> T + Sync + Send,
        T: Send + Clone,
    { ... }

    fn try_fold<T, R, ID, F>(
        self, 
        identity: ID, 
        fold_op: F
    ) -> TryFold<Self, R, ID, F>
    where
        F: Fn(T, Self::Item) -> R + Sync + Send,
        ID: Fn() -> T + Sync + Send,
        R: Try<Ok = T> + Send,
    { ... }

    fn try_fold_with<F, T, R>(
        self, 
        init: T, 
        fold_op: F
    ) -> TryFoldWith<Self, R, F>
    where
        F: Fn(T, Self::Item) -> R + Sync + Send,
        R: Try<Ok = T> + Send,
        T: Clone + Send,
    { ... }

    fn sum<S>(self) -> S
    where
        S: Send + Sum<Self::Item> + Sum<S>,
    { ... }

    fn product<P>(self) -> P
    where
        P: Send + Product<Self::Item> + Product<P>,
    { ... }

    fn min(self) -> Option<Self::Item>
    where
        Self::Item: Ord,
    { ... }

    fn min_by<F>(self, f: F) -> Option<Self::Item>
    where
        F: Sync + Send + Fn(&Self::Item, &Self::Item) -> Ordering,
    { ... }

    fn min_by_key<K, F>(self, f: F) -> Option<Self::Item>
    where
        K: Ord + Send,
        F: Sync + Send + Fn(&Self::Item) -> K,
    { ... }

    fn max(self) -> Option<Self::Item>
    where
        Self::Item: Ord,
    { ... }

    fn max_by<F>(self, f: F) -> Option<Self::Item>
    where
        F: Sync + Send + Fn(&Self::Item, &Self::Item) -> Ordering,
    { ... }

    fn max_by_key<K, F>(self, f: F) -> Option<Self::Item>
    where
        K: Ord + Send,
        F: Sync + Send + Fn(&Self::Item) -> K,
    { ... }

    fn chain<C>(self, chain: C) -> Chain<Self, C::Iter>
    where
        C: IntoParallelIterator<Item = Self::Item>,
    { ... }

    fn find_any<P>(self, predicate: P) -> Option<Self::Item>
    where
        P: Fn(&Self::Item) -> bool + Sync + Send,
    { ... }

    fn find_first<P>(self, predicate: P) -> Option<Self::Item>
    where
        P: Fn(&Self::Item) -> bool + Sync + Send,
    { ... }

    fn find_last<P>(self, predicate: P) -> Option<Self::Item>
    where
        P: Fn(&Self::Item) -> bool + Sync + Send,
    { ... }

    fn find_map_any<P, R>(self, predicate: P) -> Option<R>
    where
        P: Fn(Self::Item) -> Option<R> + Sync + Send,
        R: Send,
    { ... }

    fn find_map_first<P, R>(self, predicate: P) -> Option<R>
    where
        P: Fn(Self::Item) -> Option<R> + Sync + Send,
        R: Send,
    { ... }

    fn find_map_last<P, R>(self, predicate: P) -> Option<R>
    where
        P: Fn(Self::Item) -> Option<R> + Sync + Send,
        R: Send,
    { ... }

    fn any<P>(self, predicate: P) -> bool
    where
        P: Fn(Self::Item) -> bool + Sync + Send,
    { ... }

    fn all<P>(self, predicate: P) -> bool
    where
        P: Fn(Self::Item) -> bool + Sync + Send,
    { ... }

    fn while_some<T>(self) -> WhileSome<Self>
    where
        Self: ParallelIterator<Item = Option<T>>,
        T: Send,
    { ... }

    fn panic_fuse(self) -> PanicFuse<Self> { ... }

    fn collect<C>(self) -> C
    where
        C: FromParallelIterator<Self::Item>,
    { ... }

    fn unzip<A, B, FromA, FromB>(self) -> (FromA, FromB)
    where
        Self: ParallelIterator<Item = (A, B)>,
        FromA: Default + Send + ParallelExtend<A>,
        FromB: Default + Send + ParallelExtend<B>,
        A: Send,
        B: Send,
    { ... }

    fn partition<A, B, P>(self, predicate: P) -> (A, B)
    where
        A: Default + Send + ParallelExtend<Self::Item>,
        B: Default + Send + ParallelExtend<Self::Item>,
        P: Fn(&Self::Item) -> bool + Sync + Send,
    { ... }

    fn partition_map<A, B, P, L, R>(self, predicate: P) -> (A, B)
    where
        A: Default + Send + ParallelExtend<L>,
        B: Default + Send + ParallelExtend<R>,
        P: Fn(Self::Item) -> Either<L, R> + Sync + Send,
        L: Send,
        R: Send,
    { ... }

    fn intersperse(self, element: Self::Item) -> Intersperse<Self>
    where
        Self::Item: Clone,
    { ... }

    fn opt_len(&self) -> Option<usize> { ... }
}

Parallel version of the standard iterator trait.

The combinators on this trait are available on all parallel iterators. Additional methods can be found on the IndexedParallelIterator trait: those methods are only available for parallel iterators where the number of items is known in advance (so, e.g., after invoking filter, those methods become unavailable).

For examples of using parallel iterators, see the docs on the iter module.

Associated Types

type Item: Send

The type of item that this parallel iterator produces. For example, if you use the for_each method, this is the type of item that your closure will be invoked with.

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Required methods

fn drive_unindexed<C>(self, consumer: C) -> C::Result where
    C: UnindexedConsumer<Self::Item>, 

Internal method used to define the behavior of this parallel iterator. You should not need to call this directly.

This method causes the iterator self to start producing items and to feed them to the consumer consumer one by one. It may split the consumer before doing so to create the opportunity to produce in parallel.

See the README for more details on the internals of parallel iterators.

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Provided methods

fn for_each<OP>(self, op: OP) where
    OP: Fn(Self::Item) + Sync + Send, 

Executes OP on each item produced by the iterator, in parallel.

Examples

use rayon::prelude::*;

(0..100).into_par_iter().for_each(|x| println!("{:?}", x));

fn for_each_with<OP, T>(self, init: T, op: OP) where
    OP: Fn(&mut T, Self::Item) + Sync + Send,
    T: Send + Clone, 

Executes OP on the given init value with each item produced by the iterator, in parallel.

The init value will be cloned only as needed to be paired with the group of items in each rayon job. It does not require the type to be Sync.

Examples

use std::sync::mpsc::channel;
use rayon::prelude::*;

let (sender, receiver) = channel();

(0..5).into_par_iter().for_each_with(sender, |s, x| s.send(x).unwrap());

let mut res: Vec<_> = receiver.iter().collect();

res.sort();

assert_eq!(&res[..], &[0, 1, 2, 3, 4])

fn for_each_init<OP, INIT, T>(self, init: INIT, op: OP) where
    OP: Fn(&mut T, Self::Item) + Sync + Send,
    INIT: Fn() -> T + Sync + Send, 

Executes OP on a value returned by init with each item produced by the iterator, in parallel.

The init function will be called only as needed for a value to be paired with the group of items in each rayon job. There is no constraint on that returned type at all!

Examples

extern crate rand;
extern crate rayon;

use rand::Rng;
use rayon::prelude::*;

let mut v = vec![0u8; 1_000_000];

v.par_chunks_mut(1000)
    .for_each_init(
        || rand::thread_rng(),
        |rng, chunk| rng.fill(chunk),
    );

// There's a remote chance that this will fail...
for i in 0u8..=255 {
    assert!(v.contains(&i));
}

fn try_for_each<OP, R>(self, op: OP) -> R where
    OP: Fn(Self::Item) -> R + Sync + Send,
    R: Try<Ok = ()> + Send, 

Executes a fallible OP on each item produced by the iterator, in parallel.

If the OP returns Result::Err or Option::None, we will attempt to stop processing the rest of the items in the iterator as soon as possible, and we will return that terminating value. Otherwise, we will return an empty Result::Ok(()) or Option::Some(()). If there are multiple errors in parallel, it is not specified which will be returned.

Examples

use rayon::prelude::*;
use std::io::{self, Write};

// This will stop iteration early if there's any write error, like
// having piped output get closed on the other end.
(0..100).into_par_iter()
    .try_for_each(|x| writeln!(io::stdout(), "{:?}", x))
    .expect("expected no write errors");

fn try_for_each_with<OP, T, R>(self, init: T, op: OP) -> R where
    OP: Fn(&mut T, Self::Item) -> R + Sync + Send,
    T: Send + Clone,
    R: Try<Ok = ()> + Send, 

Executes a fallible OP on the given init value with each item produced by the iterator, in parallel.

This combines the init semantics of for_each_with() and the failure semantics of try_for_each().

Examples

use std::sync::mpsc::channel;
use rayon::prelude::*;

let (sender, receiver) = channel();

(0..5).into_par_iter()
    .try_for_each_with(sender, |s, x| s.send(x))
    .expect("expected no send errors");

let mut res: Vec<_> = receiver.iter().collect();

res.sort();

assert_eq!(&res[..], &[0, 1, 2, 3, 4])

fn try_for_each_init<OP, INIT, T, R>(self, init: INIT, op: OP) -> R where
    OP: Fn(&mut T, Self::Item) -> R + Sync + Send,
    INIT: Fn() -> T + Sync + Send,
    R: Try<Ok = ()> + Send, 

Executes a fallible OP on a value returned by init with each item produced by the iterator, in parallel.

This combines the init semantics of for_each_init() and the failure semantics of try_for_each().

Examples

extern crate rand;
extern crate rayon;

use rand::Rng;
use rayon::prelude::*;

let mut v = vec![0u8; 1_000_000];

v.par_chunks_mut(1000)
    .try_for_each_init(
        || rand::thread_rng(),
        |rng, chunk| rng.try_fill(chunk),
    )
    .expect("expected no rand errors");

// There's a remote chance that this will fail...
for i in 0u8..=255 {
    assert!(v.contains(&i));
}

fn count(self) -> usize

Counts the number of items in this parallel iterator.

Examples

use rayon::prelude::*;

let count = (0..100).into_par_iter().count();

assert_eq!(count, 100);

fn map<F, R>(self, map_op: F) -> Map<Self, F> where
    F: Fn(Self::Item) -> R + Sync + Send,
    R: Send, 

Applies map_op to each item of this iterator, producing a new iterator with the results.

Examples

use rayon::prelude::*;

let mut par_iter = (0..5).into_par_iter().map(|x| x * 2);

let doubles: Vec<_> = par_iter.collect();

assert_eq!(&doubles[..], &[0, 2, 4, 6, 8]);

fn map_with<F, T, R>(self, init: T, map_op: F) -> MapWith<Self, T, F> where
    F: Fn(&mut T, Self::Item) -> R + Sync + Send,
    T: Send + Clone,
    R: Send, 

Applies map_op to the given init value with each item of this iterator, producing a new iterator with the results.

The init value will be cloned only as needed to be paired with the group of items in each rayon job. It does not require the type to be Sync.

Examples

use std::sync::mpsc::channel;
use rayon::prelude::*;

let (sender, receiver) = channel();

let a: Vec<_> = (0..5)
                .into_par_iter()            // iterating over i32
                .map_with(sender, |s, x| {
                    s.send(x).unwrap();     // sending i32 values through the channel
                    x                       // returning i32
                })
                .collect();                 // collecting the returned values into a vector

let mut b: Vec<_> = receiver.iter()         // iterating over the values in the channel
                            .collect();     // and collecting them
b.sort();

assert_eq!(a, b);

fn map_init<F, INIT, T, R>(
    self,
    init: INIT,
    map_op: F
) -> MapInit<Self, INIT, F> where
    F: Fn(&mut T, Self::Item) -> R + Sync + Send,
    INIT: Fn() -> T + Sync + Send,
    R: Send, 

Applies map_op to a value returned by init with each item of this iterator, producing a new iterator with the results.

The init function will be called only as needed for a value to be paired with the group of items in each rayon job. There is no constraint on that returned type at all!

Examples

extern crate rand;
extern crate rayon;

use rand::Rng;
use rayon::prelude::*;

let a: Vec<_> = (1i32..1_000_000)
    .into_par_iter()
    .map_init(
        || rand::thread_rng(),  // get the thread-local RNG
        |rng, x| if rng.gen() { // randomly negate items
            -x
        } else {
            x
        },
    ).collect();

// There's a remote chance that this will fail...
assert!(a.iter().any(|&x| x < 0));
assert!(a.iter().any(|&x| x > 0));

fn cloned<'a, T>(self) -> Cloned<Self> where
    T: 'a + Clone + Send,
    Self: ParallelIterator<Item = &'a T>, 

Creates an iterator which clones all of its elements. This may be useful when you have an iterator over &T, but you need T, and that type implements Clone. See also copied().

Examples

use rayon::prelude::*;

let a = [1, 2, 3];

let v_cloned: Vec<_> = a.par_iter().cloned().collect();

// cloned is the same as .map(|&x| x), for integers
let v_map: Vec<_> = a.par_iter().map(|&x| x).collect();

assert_eq!(v_cloned, vec![1, 2, 3]);
assert_eq!(v_map, vec![1, 2, 3]);

fn copied<'a, T>(self) -> Copied<Self> where
    T: 'a + Copy + Send,
    Self: ParallelIterator<Item = &'a T>, 

Creates an iterator which copies all of its elements. This may be useful when you have an iterator over &T, but you need T, and that type implements Copy. See also cloned().

Examples

use rayon::prelude::*;

let a = [1, 2, 3];

let v_copied: Vec<_> = a.par_iter().copied().collect();

// copied is the same as .map(|&x| x), for integers
let v_map: Vec<_> = a.par_iter().map(|&x| x).collect();

assert_eq!(v_copied, vec![1, 2, 3]);
assert_eq!(v_map, vec![1, 2, 3]);

fn inspect<OP>(self, inspect_op: OP) -> Inspect<Self, OP> where
    OP: Fn(&Self::Item) + Sync + Send, 

Applies inspect_op to a reference to each item of this iterator, producing a new iterator passing through the original items. This is often useful for debugging to see what's happening in iterator stages.

Examples

use rayon::prelude::*;

let a = [1, 4, 2, 3];

// this iterator sequence is complex.
let sum = a.par_iter()
            .cloned()
            .filter(|&x| x % 2 == 0)
            .reduce(|| 0, |sum, i| sum + i);

println!("{}", sum);

// let's add some inspect() calls to investigate what's happening
let sum = a.par_iter()
            .cloned()
            .inspect(|x| println!("about to filter: {}", x))
            .filter(|&x| x % 2 == 0)
            .inspect(|x| println!("made it through filter: {}", x))
            .reduce(|| 0, |sum, i| sum + i);

println!("{}", sum);

fn update<F>(self, update_op: F) -> Update<Self, F> where
    F: Fn(&mut Self::Item) + Sync + Send, 

Mutates each item of this iterator before yielding it.

Examples

use rayon::prelude::*;

let par_iter = (0..5).into_par_iter().update(|x| {*x *= 2;});

let doubles: Vec<_> = par_iter.collect();

assert_eq!(&doubles[..], &[0, 2, 4, 6, 8]);

fn filter<P>(self, filter_op: P) -> Filter<Self, P> where
    P: Fn(&Self::Item) -> bool + Sync + Send, 

Applies filter_op to each item of this iterator, producing a new iterator with only the items that gave true results.

Examples

use rayon::prelude::*;

let mut par_iter = (0..10).into_par_iter().filter(|x| x % 2 == 0);

let even_numbers: Vec<_> = par_iter.collect();

assert_eq!(&even_numbers[..], &[0, 2, 4, 6, 8]);

fn filter_map<P, R>(self, filter_op: P) -> FilterMap<Self, P> where
    P: Fn(Self::Item) -> Option<R> + Sync + Send,
    R: Send, 

Applies filter_op to each item of this iterator to get an Option, producing a new iterator with only the items from Some results.

Examples

use rayon::prelude::*;

let mut par_iter = (0..10).into_par_iter()
                        .filter_map(|x| {
                            if x % 2 == 0 { Some(x * 3) }
                            else { None }
                        });

let even_numbers: Vec<_> = par_iter.collect();

assert_eq!(&even_numbers[..], &[0, 6, 12, 18, 24]);

fn flat_map<F, PI>(self, map_op: F) -> FlatMap<Self, F> where
    F: Fn(Self::Item) -> PI + Sync + Send,
    PI: IntoParallelIterator, 

Applies map_op to each item of this iterator to get nested iterators, producing a new iterator that flattens these back into one.

Examples

use rayon::prelude::*;

let a = [[1, 2], [3, 4], [5, 6], [7, 8]];

let par_iter = a.par_iter().cloned().flat_map(|a| a.to_vec());

let vec: Vec<_> = par_iter.collect();

assert_eq!(&vec[..], &[1, 2, 3, 4, 5, 6, 7, 8]);

fn flatten(self) -> Flatten<Self> where
    Self::Item: IntoParallelIterator, 

An adaptor that flattens iterable Items into one large iterator

Examples

use rayon::prelude::*;

let x: Vec<Vec<_>> = vec![vec![1, 2], vec![3, 4]];
let y: Vec<_> = x.into_par_iter().flatten().collect();

assert_eq!(y, vec![1, 2, 3, 4]);

fn reduce<OP, ID>(self, identity: ID, op: OP) -> Self::Item where
    OP: Fn(Self::Item, Self::Item) -> Self::Item + Sync + Send,
    ID: Fn() -> Self::Item + Sync + Send, 

Reduces the items in the iterator into one item using op. The argument identity should be a closure that can produce "identity" value which may be inserted into the sequence as needed to create opportunities for parallel execution. So, for example, if you are doing a summation, then identity() ought to produce something that represents the zero for your type (but consider just calling sum() in that case).

Examples

// Iterate over a sequence of pairs `(x0, y0), ..., (xN, yN)`
// and use reduce to compute one pair `(x0 + ... + xN, y0 + ... + yN)`
// where the first/second elements are summed separately.
use rayon::prelude::*;
let sums = [(0, 1), (5, 6), (16, 2), (8, 9)]
           .par_iter()        // iterating over &(i32, i32)
           .cloned()          // iterating over (i32, i32)
           .reduce(|| (0, 0), // the "identity" is 0 in both columns
                   |a, b| (a.0 + b.0, a.1 + b.1));
assert_eq!(sums, (0 + 5 + 16 + 8, 1 + 6 + 2 + 9));

Note: unlike a sequential fold operation, the order in which op will be applied to reduce the result is not fully specified. So op should be associative or else the results will be non-deterministic. And of course identity() should produce a true identity.

fn reduce_with<OP>(self, op: OP) -> Option<Self::Item> where
    OP: Fn(Self::Item, Self::Item) -> Self::Item + Sync + Send, 

Reduces the items in the iterator into one item using op. If the iterator is empty, None is returned; otherwise, Some is returned.

This version of reduce is simple but somewhat less efficient. If possible, it is better to call reduce(), which requires an identity element.

Examples

use rayon::prelude::*;
let sums = [(0, 1), (5, 6), (16, 2), (8, 9)]
           .par_iter()        // iterating over &(i32, i32)
           .cloned()          // iterating over (i32, i32)
           .reduce_with(|a, b| (a.0 + b.0, a.1 + b.1))
           .unwrap();
assert_eq!(sums, (0 + 5 + 16 + 8, 1 + 6 + 2 + 9));

Note: unlike a sequential fold operation, the order in which op will be applied to reduce the result is not fully specified. So op should be associative or else the results will be non-deterministic.

fn try_reduce<T, OP, ID>(self, identity: ID, op: OP) -> Self::Item where
    OP: Fn(T, T) -> Self::Item + Sync + Send,
    ID: Fn() -> T + Sync + Send,
    Self::Item: Try<Ok = T>, 

Reduces the items in the iterator into one item using a fallible op. The identity argument is used the same way as in reduce().

If a Result::Err or Option::None item is found, or if op reduces to one, we will attempt to stop processing the rest of the items in the iterator as soon as possible, and we will return that terminating value. Otherwise, we will return the final reduced Result::Ok(T) or Option::Some(T). If there are multiple errors in parallel, it is not specified which will be returned.

Examples

use rayon::prelude::*;

// Compute the sum of squares, being careful about overflow.
fn sum_squares<I: IntoParallelIterator<Item = i32>>(iter: I) -> Option<i32> {
    iter.into_par_iter()
        .map(|i| i.checked_mul(i))            // square each item,
        .try_reduce(|| 0, i32::checked_add)   // and add them up!
}
assert_eq!(sum_squares(0..5), Some(0 + 1 + 4 + 9 + 16));

// The sum might overflow
assert_eq!(sum_squares(0..10_000), None);

// Or the squares might overflow before it even reaches `try_reduce`
assert_eq!(sum_squares(1_000_000..1_000_001), None);

fn try_reduce_with<T, OP>(self, op: OP) -> Option<Self::Item> where
    OP: Fn(T, T) -> Self::Item + Sync + Send,
    Self::Item: Try<Ok = T>, 

Reduces the items in the iterator into one item using a fallible op.

Like reduce_with(), if the iterator is empty, None is returned; otherwise, Some is returned. Beyond that, it behaves like try_reduce() for handling Err/None.

For instance, with Option items, the return value may be:

  • None, the iterator was empty
  • Some(None), we stopped after encountering None.
  • Some(Some(x)), the entire iterator reduced to x.

With Result items, the nesting is more obvious:

  • None, the iterator was empty
  • Some(Err(e)), we stopped after encountering an error e.
  • Some(Ok(x)), the entire iterator reduced to x.

Examples

use rayon::prelude::*;

let files = ["/dev/null", "/does/not/exist"];

// Find the biggest file
files.into_par_iter()
    .map(|path| std::fs::metadata(path).map(|m| (path, m.len())))
    .try_reduce_with(|a, b| {
        Ok(if a.1 >= b.1 { a } else { b })
    })
    .expect("Some value, since the iterator is not empty")
    .expect_err("not found");

fn fold<T, ID, F>(self, identity: ID, fold_op: F) -> Fold<Self, ID, F> where
    F: Fn(T, Self::Item) -> T + Sync + Send,
    ID: Fn() -> T + Sync + Send,
    T: Send, 

Parallel fold is similar to sequential fold except that the sequence of items may be subdivided before it is folded. Consider a list of numbers like 22 3 77 89 46. If you used sequential fold to add them (fold(0, |a,b| a+b), you would wind up first adding 0 + 22, then 22 + 3, then 25 + 77, and so forth. The parallel fold works similarly except that it first breaks up your list into sublists, and hence instead of yielding up a single sum at the end, it yields up multiple sums. The number of results is nondeterministic, as is the point where the breaks occur.

So if did the same parallel fold (fold(0, |a,b| a+b)) on our example list, we might wind up with a sequence of two numbers, like so:

22 3 77 89 46
      |     |
    102   135

Or perhaps these three numbers:

22 3 77 89 46
      |  |  |
    102 89 46

In general, Rayon will attempt to find good breaking points that keep all of your cores busy.

Fold versus reduce

The fold() and reduce() methods each take an identity element and a combining function, but they operate rather differently.

reduce() requires that the identity function has the same type as the things you are iterating over, and it fully reduces the list of items into a single item. So, for example, imagine we are iterating over a list of bytes bytes: [128_u8, 64_u8, 64_u8]. If we used bytes.reduce(|| 0_u8, |a: u8, b: u8| a + b), we would get an overflow. This is because 0, a, and b here are all bytes, just like the numbers in the list (I wrote the types explicitly above, but those are the only types you can use). To avoid the overflow, we would need to do something like bytes.map(|b| b as u32).reduce(|| 0, |a, b| a + b), in which case our result would be 256.

In contrast, with fold(), the identity function does not have to have the same type as the things you are iterating over, and you potentially get back many results. So, if we continue with the bytes example from the previous paragraph, we could do bytes.fold(|| 0_u32, |a, b| a + (b as u32)) to convert our bytes into u32. And of course we might not get back a single sum.

There is a more subtle distinction as well, though it's actually implied by the above points. When you use reduce(), your reduction function is sometimes called with values that were never part of your original parallel iterator (for example, both the left and right might be a partial sum). With fold(), in contrast, the left value in the fold function is always the accumulator, and the right value is always from your original sequence.

Fold vs Map/Reduce

Fold makes sense if you have some operation where it is cheaper to create groups of elements at a time. For example, imagine collecting characters into a string. If you were going to use map/reduce, you might try this:

use rayon::prelude::*;

let s =
    ['a', 'b', 'c', 'd', 'e']
    .par_iter()
    .map(|c: &char| format!("{}", c))
    .reduce(|| String::new(),
            |mut a: String, b: String| { a.push_str(&b); a });

assert_eq!(s, "abcde");

Because reduce produces the same type of element as its input, you have to first map each character into a string, and then you can reduce them. This means we create one string per element in our iterator -- not so great. Using fold, we can do this instead:

use rayon::prelude::*;

let s =
    ['a', 'b', 'c', 'd', 'e']
    .par_iter()
    .fold(|| String::new(),
            |mut s: String, c: &char| { s.push(*c); s })
    .reduce(|| String::new(),
            |mut a: String, b: String| { a.push_str(&b); a });

assert_eq!(s, "abcde");

Now fold will process groups of our characters at a time, and we only make one string per group. We should wind up with some small-ish number of strings roughly proportional to the number of CPUs you have (it will ultimately depend on how busy your processors are). Note that we still need to do a reduce afterwards to combine those groups of strings into a single string.

You could use a similar trick to save partial results (e.g., a cache) or something similar.

Combining fold with other operations

You can combine fold with reduce if you want to produce a single value. This is then roughly equivalent to a map/reduce combination in effect:

use rayon::prelude::*;

let bytes = 0..22_u8;
let sum = bytes.into_par_iter()
               .fold(|| 0_u32, |a: u32, b: u8| a + (b as u32))
               .sum::<u32>();

assert_eq!(sum, (0..22).sum()); // compare to sequential

fn fold_with<F, T>(self, init: T, fold_op: F) -> FoldWith<Self, T, F> where
    F: Fn(T, Self::Item) -> T + Sync + Send,
    T: Send + Clone, 

Applies fold_op to the given init value with each item of this iterator, finally producing the value for further use.

This works essentially like fold(|| init.clone(), fold_op), except it doesn't require the init type to be Sync, nor any other form of added synchronization.

Examples

use rayon::prelude::*;

let bytes = 0..22_u8;
let sum = bytes.into_par_iter()
               .fold_with(0_u32, |a: u32, b: u8| a + (b as u32))
               .sum::<u32>();

assert_eq!(sum, (0..22).sum()); // compare to sequential

fn try_fold<T, R, ID, F>(
    self,
    identity: ID,
    fold_op: F
) -> TryFold<Self, R, ID, F> where
    F: Fn(T, Self::Item) -> R + Sync + Send,
    ID: Fn() -> T + Sync + Send,
    R: Try<Ok = T> + Send, 

Perform a fallible parallel fold.

This is a variation of fold() for operations which can fail with Option::None or Result::Err. The first such failure stops processing the local set of items, without affecting other folds in the iterator's subdivisions.

Often, try_fold() will be followed by try_reduce() for a final reduction and global short-circuiting effect.

Examples

use rayon::prelude::*;

let bytes = 0..22_u8;
let sum = bytes.into_par_iter()
               .try_fold(|| 0_u32, |a: u32, b: u8| a.checked_add(b as u32))
               .try_reduce(|| 0, u32::checked_add);

assert_eq!(sum, Some((0..22).sum())); // compare to sequential

fn try_fold_with<F, T, R>(self, init: T, fold_op: F) -> TryFoldWith<Self, R, F> where
    F: Fn(T, Self::Item) -> R + Sync + Send,
    R: Try<Ok = T> + Send,
    T: Clone + Send, 

Perform a fallible parallel fold with a cloneable init value.

This combines the init semantics of fold_with() and the failure semantics of try_fold().

use rayon::prelude::*;

let bytes = 0..22_u8;
let sum = bytes.into_par_iter()
               .try_fold_with(0_u32, |a: u32, b: u8| a.checked_add(b as u32))
               .try_reduce(|| 0, u32::checked_add);

assert_eq!(sum, Some((0..22).sum())); // compare to sequential

fn sum<S>(self) -> S where
    S: Send + Sum<Self::Item> + Sum<S>, 

Sums up the items in the iterator.

Note that the order in items will be reduced is not specified, so if the + operator is not truly associative (as is the case for floating point numbers), then the results are not fully deterministic.

Basically equivalent to self.reduce(|| 0, |a, b| a + b), except that the type of 0 and the + operation may vary depending on the type of value being produced.

Examples

use rayon::prelude::*;

let a = [1, 5, 7];

let sum: i32 = a.par_iter().sum();

assert_eq!(sum, 13);

fn product<P>(self) -> P where
    P: Send + Product<Self::Item> + Product<P>, 

Multiplies all the items in the iterator.

Note that the order in items will be reduced is not specified, so if the * operator is not truly associative (as is the case for floating point numbers), then the results are not fully deterministic.

Basically equivalent to self.reduce(|| 1, |a, b| a * b), except that the type of 1 and the * operation may vary depending on the type of value being produced.

Examples

use rayon::prelude::*;

fn factorial(n: u32) -> u32 {
   (1..n+1).into_par_iter().product()
}

assert_eq!(factorial(0), 1);
assert_eq!(factorial(1), 1);
assert_eq!(factorial(5), 120);

fn min(self) -> Option<Self::Item> where
    Self::Item: Ord, 

Computes the minimum of all the items in the iterator. If the iterator is empty, None is returned; otherwise, Some(min) is returned.

Note that the order in which the items will be reduced is not specified, so if the Ord impl is not truly associative, then the results are not deterministic.

Basically equivalent to self.reduce_with(|a, b| cmp::min(a, b)).

Examples

use rayon::prelude::*;

let a = [45, 74, 32];

assert_eq!(a.par_iter().min(), Some(&32));

let b: [i32; 0] = [];

assert_eq!(b.par_iter().min(), None);

fn min_by<F>(self, f: F) -> Option<Self::Item> where
    F: Sync + Send + Fn(&Self::Item, &Self::Item) -> Ordering, 

Computes the minimum of all the items in the iterator with respect to the given comparison function. If the iterator is empty, None is returned; otherwise, Some(min) is returned.

Note that the order in which the items will be reduced is not specified, so if the comparison function is not associative, then the results are not deterministic.

Examples

use rayon::prelude::*;

let a = [-3_i32, 77, 53, 240, -1];

assert_eq!(a.par_iter().min_by(|x, y| x.cmp(y)), Some(&-3));

fn min_by_key<K, F>(self, f: F) -> Option<Self::Item> where
    K: Ord + Send,
    F: Sync + Send + Fn(&Self::Item) -> K, 

Computes the item that yields the minimum value for the given function. If the iterator is empty, None is returned; otherwise, Some(item) is returned.

Note that the order in which the items will be reduced is not specified, so if the Ord impl is not truly associative, then the results are not deterministic.

Examples

use rayon::prelude::*;

let a = [-3_i32, 34, 2, 5, -10, -3, -23];

assert_eq!(a.par_iter().min_by_key(|x| x.abs()), Some(&2));

fn max(self) -> Option<Self::Item> where
    Self::Item: Ord, 

Computes the maximum of all the items in the iterator. If the iterator is empty, None is returned; otherwise, Some(max) is returned.

Note that the order in which the items will be reduced is not specified, so if the Ord impl is not truly associative, then the results are not deterministic.

Basically equivalent to self.reduce_with(|a, b| cmp::max(a, b)).

Examples

use rayon::prelude::*;

let a = [45, 74, 32];

assert_eq!(a.par_iter().max(), Some(&74));

let b: [i32; 0] = [];

assert_eq!(b.par_iter().max(), None);

fn max_by<F>(self, f: F) -> Option<Self::Item> where
    F: Sync + Send + Fn(&Self::Item, &Self::Item) -> Ordering, 

Computes the maximum of all the items in the iterator with respect to the given comparison function. If the iterator is empty, None is returned; otherwise, Some(min) is returned.

Note that the order in which the items will be reduced is not specified, so if the comparison function is not associative, then the results are not deterministic.

Examples

use rayon::prelude::*;

let a = [-3_i32, 77, 53, 240, -1];

assert_eq!(a.par_iter().max_by(|x, y| x.abs().cmp(&y.abs())), Some(&240));

fn max_by_key<K, F>(self, f: F) -> Option<Self::Item> where
    K: Ord + Send,
    F: Sync + Send + Fn(&Self::Item) -> K, 

Computes the item that yields the maximum value for the given function. If the iterator is empty, None is returned; otherwise, Some(item) is returned.

Note that the order in which the items will be reduced is not specified, so if the Ord impl is not truly associative, then the results are not deterministic.

Examples

use rayon::prelude::*;

let a = [-3_i32, 34, 2, 5, -10, -3, -23];

assert_eq!(a.par_iter().max_by_key(|x| x.abs()), Some(&34));

fn chain<C>(self, chain: C) -> Chain<Self, C::Iter> where
    C: IntoParallelIterator<Item = Self::Item>, 

Takes two iterators and creates a new iterator over both.

Examples

use rayon::prelude::*;

let a = [0, 1, 2];
let b = [9, 8, 7];

let par_iter = a.par_iter().chain(b.par_iter());

let chained: Vec<_> = par_iter.cloned().collect();

assert_eq!(&chained[..], &[0, 1, 2, 9, 8, 7]);

fn find_any<P>(self, predicate: P) -> Option<Self::Item> where
    P: Fn(&Self::Item) -> bool + Sync + Send, 

Searches for some item in the parallel iterator that matches the given predicate and returns it. This operation is similar to find on sequential iterators but the item returned may not be the first one in the parallel sequence which matches, since we search the entire sequence in parallel.

Once a match is found, we will attempt to stop processing the rest of the items in the iterator as soon as possible (just as find stops iterating once a match is found).

Examples

use rayon::prelude::*;

let a = [1, 2, 3, 3];

assert_eq!(a.par_iter().find_any(|&&x| x == 3), Some(&3));

assert_eq!(a.par_iter().find_any(|&&x| x == 100), None);

fn find_first<P>(self, predicate: P) -> Option<Self::Item> where
    P: Fn(&Self::Item) -> bool + Sync + Send, 

Searches for the sequentially first item in the parallel iterator that matches the given predicate and returns it.

Once a match is found, all attempts to the right of the match will be stopped, while attempts to the left must continue in case an earlier match is found.

Note that not all parallel iterators have a useful order, much like sequential HashMap iteration, so "first" may be nebulous. If you just want the first match that discovered anywhere in the iterator, find_any is a better choice.

Examples

use rayon::prelude::*;

let a = [1, 2, 3, 3];

assert_eq!(a.par_iter().find_first(|&&x| x == 3), Some(&3));

assert_eq!(a.par_iter().find_first(|&&x| x == 100), None);

fn find_last<P>(self, predicate: P) -> Option<Self::Item> where
    P: Fn(&Self::Item) -> bool + Sync + Send, 

Searches for the sequentially last item in the parallel iterator that matches the given predicate and returns it.

Once a match is found, all attempts to the left of the match will be stopped, while attempts to the right must continue in case a later match is found.

Note that not all parallel iterators have a useful order, much like sequential HashMap iteration, so "last" may be nebulous. When the order doesn't actually matter to you, find_any is a better choice.

Examples

use rayon::prelude::*;

let a = [1, 2, 3, 3];

assert_eq!(a.par_iter().find_last(|&&x| x == 3), Some(&3));

assert_eq!(a.par_iter().find_last(|&&x| x == 100), None);

fn find_map_any<P, R>(self, predicate: P) -> Option<R> where
    P: Fn(Self::Item) -> Option<R> + Sync + Send,
    R: Send, 

Applies the given predicate to the items in the parallel iterator and returns any non-None result of the map operation.

Once a non-None value is produced from the map operation, we will attempt to stop processing the rest of the items in the iterator as soon as possible.

Note that this method only returns some item in the parallel iterator that is not None from the map predicate. The item returned may not be the first non-None value produced in the parallel sequence, since the entire sequence is mapped over in parallel.

Examples

use rayon::prelude::*;

let c = ["lol", "NaN", "5", "5"];

let first_number = c.par_iter().find_map_first(|s| s.parse().ok());

assert_eq!(first_number, Some(5));

fn find_map_first<P, R>(self, predicate: P) -> Option<R> where
    P: Fn(Self::Item) -> Option<R> + Sync + Send,
    R: Send, 

Applies the given predicate to the items in the parallel iterator and returns the sequentially first non-None result of the map operation.

Once a non-None value is produced from the map operation, all attempts to the right of the match will be stopped, while attempts to the left must continue in case an earlier match is found.

Note that not all parallel iterators have a useful order, much like sequential HashMap iteration, so "first" may be nebulous. If you just want the first non-None value discovered anywhere in the iterator, find_map_any is a better choice.

Examples

use rayon::prelude::*;

let c = ["lol", "NaN", "2", "5"];

let first_number = c.par_iter().find_map_first(|s| s.parse().ok());

assert_eq!(first_number, Some(2));

fn find_map_last<P, R>(self, predicate: P) -> Option<R> where
    P: Fn(Self::Item) -> Option<R> + Sync + Send,
    R: Send, 

Applies the given predicate to the items in the parallel iterator and returns the sequentially last non-None result of the map operation.

Once a non-None value is produced from the map operation, all attempts to the left of the match will be stopped, while attempts to the right must continue in case a later match is found.

Note that not all parallel iterators have a useful order, much like sequential HashMap iteration, so "first" may be nebulous. If you just want the first non-None value discovered anywhere in the iterator, find_map_any is a better choice.

Examples

use rayon::prelude::*;

let c = ["lol", "NaN", "2", "5"];

let first_number = c.par_iter().find_map_last(|s| s.parse().ok());

assert_eq!(first_number, Some(5));

fn any<P>(self, predicate: P) -> bool where
    P: Fn(Self::Item) -> bool + Sync + Send, 

Searches for some item in the parallel iterator that matches the given predicate, and if so returns true. Once a match is found, we'll attempt to stop process the rest of the items. Proving that there's no match, returning false, does require visiting every item.

Examples

use rayon::prelude::*;

let a = [0, 12, 3, 4, 0, 23, 0];

let is_valid = a.par_iter().any(|&x| x > 10);

assert!(is_valid);

fn all<P>(self, predicate: P) -> bool where
    P: Fn(Self::Item) -> bool + Sync + Send, 

Tests that every item in the parallel iterator matches the given predicate, and if so returns true. If a counter-example is found, we'll attempt to stop processing more items, then return false.

Examples

use rayon::prelude::*;

let a = [0, 12, 3, 4, 0, 23, 0];

let is_valid = a.par_iter().all(|&x| x > 10);

assert!(!is_valid);

fn while_some<T>(self) -> WhileSome<Self> where
    Self: ParallelIterator<Item = Option<T>>,
    T: Send, 

Creates an iterator over the Some items of this iterator, halting as soon as any None is found.

Examples

use rayon::prelude::*;
use std::sync::atomic::{AtomicUsize, Ordering};

let counter = AtomicUsize::new(0);
let value = (0_i32..2048)
    .into_par_iter()
    .map(|x| {
             counter.fetch_add(1, Ordering::SeqCst);
             if x < 1024 { Some(x) } else { None }
         })
    .while_some()
    .max();

assert!(value < Some(1024));
assert!(counter.load(Ordering::SeqCst) < 2048); // should not have visited every single one

fn panic_fuse(self) -> PanicFuse<Self>

Wraps an iterator with a fuse in case of panics, to halt all threads as soon as possible.

Panics within parallel iterators are always propagated to the caller, but they don't always halt the rest of the iterator right away, due to the internal semantics of join. This adaptor makes a greater effort to stop processing other items sooner, with the cost of additional synchronization overhead, which may also inhibit some optimizations.

Examples

If this code didn't use panic_fuse(), it would continue processing many more items in other threads (with long sleep delays) before the panic is finally propagated.

use rayon::prelude::*;
use std::{thread, time};

(0..1_000_000)
    .into_par_iter()
    .panic_fuse()
    .for_each(|i| {
        // simulate some work
        thread::sleep(time::Duration::from_secs(1));
        assert!(i > 0); // oops!
    });

fn collect<C>(self) -> C where
    C: FromParallelIterator<Self::Item>, 

Create a fresh collection containing all the element produced by this parallel iterator.

You may prefer to use collect_into_vec(), which allocates more efficiently with precise knowledge of how many elements the iterator contains, and even allows you to reuse an existing vector's backing store rather than allocating a fresh vector.

Examples

use rayon::prelude::*;

let sync_vec: Vec<_> = (0..100).into_iter().collect();

let async_vec: Vec<_> = (0..100).into_par_iter().collect();

assert_eq!(sync_vec, async_vec);

fn unzip<A, B, FromA, FromB>(self) -> (FromA, FromB) where
    Self: ParallelIterator<Item = (A, B)>,
    FromA: Default + Send + ParallelExtend<A>,
    FromB: Default + Send + ParallelExtend<B>,
    A: Send,
    B: Send, 

Unzips the items of a parallel iterator into a pair of arbitrary ParallelExtend containers.

You may prefer to use unzip_into_vecs(), which allocates more efficiently with precise knowledge of how many elements the iterator contains, and even allows you to reuse existing vectors' backing stores rather than allocating fresh vectors.

Examples

use rayon::prelude::*;

let a = [(0, 1), (1, 2), (2, 3), (3, 4)];

let (left, right): (Vec<_>, Vec<_>) = a.par_iter().cloned().unzip();

assert_eq!(left, [0, 1, 2, 3]);
assert_eq!(right, [1, 2, 3, 4]);

Nested pairs can be unzipped too.

use rayon::prelude::*;

let (values, (squares, cubes)): (Vec<_>, (Vec<_>, Vec<_>)) = (0..4).into_par_iter()
    .map(|i| (i, (i * i, i * i * i)))
    .unzip();

assert_eq!(values, [0, 1, 2, 3]);
assert_eq!(squares, [0, 1, 4, 9]);
assert_eq!(cubes, [0, 1, 8, 27]);

fn partition<A, B, P>(self, predicate: P) -> (A, B) where
    A: Default + Send + ParallelExtend<Self::Item>,
    B: Default + Send + ParallelExtend<Self::Item>,
    P: Fn(&Self::Item) -> bool + Sync + Send, 

Partitions the items of a parallel iterator into a pair of arbitrary ParallelExtend containers. Items for which the predicate returns true go into the first container, and the rest go into the second.

Note: unlike the standard Iterator::partition, this allows distinct collection types for the left and right items. This is more flexible, but may require new type annotations when converting sequential code that used type inferrence assuming the two were the same.

Examples

use rayon::prelude::*;

let (left, right): (Vec<_>, Vec<_>) = (0..8).into_par_iter().partition(|x| x % 2 == 0);

assert_eq!(left, [0, 2, 4, 6]);
assert_eq!(right, [1, 3, 5, 7]);

fn partition_map<A, B, P, L, R>(self, predicate: P) -> (A, B) where
    A: Default + Send + ParallelExtend<L>,
    B: Default + Send + ParallelExtend<R>,
    P: Fn(Self::Item) -> Either<L, R> + Sync + Send,
    L: Send,
    R: Send, 

Partitions and maps the items of a parallel iterator into a pair of arbitrary ParallelExtend containers. Either::Left items go into the first container, and Either::Right items go into the second.

Examples

use rayon::prelude::*;
use rayon::iter::Either;

let (left, right): (Vec<_>, Vec<_>) = (0..8).into_par_iter()
    .partition_map(|x| {
        if x % 2 == 0 {
            Either::Left(x * 4)
        } else {
            Either::Right(x * 3)
        }
    });

assert_eq!(left, [0, 8, 16, 24]);
assert_eq!(right, [3, 9, 15, 21]);

Nested Either enums can be split as well.

use rayon::prelude::*;
use rayon::iter::Either::*;

let ((fizzbuzz, fizz), (buzz, other)): ((Vec<_>, Vec<_>), (Vec<_>, Vec<_>)) = (1..20)
    .into_par_iter()
    .partition_map(|x| match (x % 3, x % 5) {
        (0, 0) => Left(Left(x)),
        (0, _) => Left(Right(x)),
        (_, 0) => Right(Left(x)),
        (_, _) => Right(Right(x)),
    });

assert_eq!(fizzbuzz, [15]);
assert_eq!(fizz, [3, 6, 9, 12, 18]);
assert_eq!(buzz, [5, 10]);
assert_eq!(other, [1, 2, 4, 7, 8, 11, 13, 14, 16, 17, 19]);

fn intersperse(self, element: Self::Item) -> Intersperse<Self> where
    Self::Item: Clone, 

Intersperses clones of an element between items of this iterator.

Examples

use rayon::prelude::*;

let x = vec![1, 2, 3];
let r: Vec<_> = x.into_par_iter().intersperse(-1).collect();

assert_eq!(r, vec![1, -1, 2, -1, 3]);

fn opt_len(&self) -> Option<usize>

Internal method used to define the behavior of this parallel iterator. You should not need to call this directly.

Returns the number of items produced by this iterator, if known statically. This can be used by consumers to trigger special fast paths. Therefore, if Some(_) is returned, this iterator must only use the (indexed) Consumer methods when driving a consumer, such as split_at(). Calling UnindexedConsumer::split_off_left() or other UnindexedConsumer methods -- or returning an inaccurate value -- may result in panics.

This method is currently used to optimize collect for want of true Rust specialization; it may be removed when specialization is stable.

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Implementors

impl ParallelIterator for rayon::range::Iter<i128>[src]

type Item = i128

impl ParallelIterator for rayon::range::Iter<i16>[src]

type Item = i16

impl ParallelIterator for rayon::range::Iter<i32>[src]

type Item = i32

impl ParallelIterator for rayon::range::Iter<i64>[src]

type Item = i64

impl ParallelIterator for rayon::range::Iter<i8>[src]

type Item = i8

impl ParallelIterator for rayon::range::Iter<isize>[src]

type Item = isize

impl ParallelIterator for rayon::range::Iter<u128>[src]

type Item = u128

impl ParallelIterator for rayon::range::Iter<u16>[src]

type Item = u16

impl ParallelIterator for rayon::range::Iter<u32>[src]

type Item = u32

impl ParallelIterator for rayon::range::Iter<u64>[src]

type Item = u64

impl ParallelIterator for rayon::range::Iter<u8>[src]

type Item = u8

impl ParallelIterator for rayon::range::Iter<usize>[src]

type Item = usize

impl ParallelIterator for rayon::range_inclusive::Iter<i128>[src]

type Item = i128

impl ParallelIterator for rayon::range_inclusive::Iter<i16>[src]

type Item = i16

impl ParallelIterator for rayon::range_inclusive::Iter<i32>[src]

type Item = i32

impl ParallelIterator for rayon::range_inclusive::Iter<i64>[src]

type Item = i64

impl ParallelIterator for rayon::range_inclusive::Iter<i8>[src]

type Item = i8

impl ParallelIterator for rayon::range_inclusive::Iter<isize>[src]

type Item = isize

impl ParallelIterator for rayon::range_inclusive::Iter<u128>[src]

type Item = u128

impl ParallelIterator for rayon::range_inclusive::Iter<u16>[src]

type Item = u16

impl ParallelIterator for rayon::range_inclusive::Iter<u32>[src]

type Item = u32

impl ParallelIterator for rayon::range_inclusive::Iter<u64>[src]

type Item = u64

impl ParallelIterator for rayon::range_inclusive::Iter<u8>[src]

type Item = u8

impl ParallelIterator for rayon::range_inclusive::Iter<usize>[src]

type Item = usize

impl<'a, K: Ord + Sync + 'a, V: Send + 'a> ParallelIterator for rayon::collections::btree_map::IterMut<'a, K, V>[src]

type Item = (&'a K, &'a mut V)

impl<'a, K: Ord + Sync + 'a, V: Sync + 'a> ParallelIterator for rayon::collections::btree_map::Iter<'a, K, V>[src]

type Item = (&'a K, &'a V)

impl<'a, K: Hash + Eq + Sync + 'a, V: Send + 'a> ParallelIterator for rayon::collections::hash_map::IterMut<'a, K, V>[src]

type Item = (&'a K, &'a mut V)

impl<'a, K: Hash + Eq + Sync + 'a, V: Sync + 'a> ParallelIterator for rayon::collections::hash_map::Iter<'a, K, V>[src]

type Item = (&'a K, &'a V)

impl<'a, T, I> ParallelIterator for Cloned<I> where
    I: ParallelIterator<Item = &'a T>,
    T: 'a + Clone + Send + Sync, [src]

type Item = T

impl<'a, T, I> ParallelIterator for Copied<I> where
    I: ParallelIterator<Item = &'a T>,
    T: 'a + Copy + Send + Sync, [src]

type Item = T

impl<'a, T: Ord + Sync + 'a> ParallelIterator for rayon::collections::binary_heap::Iter<'a, T>[src]

type Item = &'a T

impl<'a, T: Ord + Sync + 'a> ParallelIterator for rayon::collections::btree_set::Iter<'a, T>[src]

type Item = &'a T

impl<'a, T: Hash + Eq + Sync + 'a> ParallelIterator for rayon::collections::hash_set::Iter<'a, T>[src]

type Item = &'a T

impl<'a, T: Send + 'a> ParallelIterator for rayon::collections::linked_list::IterMut<'a, T>[src]

type Item = &'a mut T

impl<'a, T: Send + 'a> ParallelIterator for rayon::collections::vec_deque::IterMut<'a, T>[src]

type Item = &'a mut T

impl<'a, T: Send + 'a> ParallelIterator for rayon::option::IterMut<'a, T>[src]

type Item = &'a mut T

impl<'a, T: Send + 'a> ParallelIterator for rayon::result::IterMut<'a, T>[src]

type Item = &'a mut T

impl<'a, T: Sync + 'a> ParallelIterator for rayon::collections::linked_list::Iter<'a, T>[src]

type Item = &'a T

impl<'a, T: Sync + 'a> ParallelIterator for rayon::collections::vec_deque::Iter<'a, T>[src]

type Item = &'a T

impl<'a, T: Sync + 'a> ParallelIterator for rayon::option::Iter<'a, T>[src]

type Item = &'a T

impl<'a, T: Sync + 'a> ParallelIterator for rayon::result::Iter<'a, T>[src]

type Item = &'a T

impl<'ch> ParallelIterator for Bytes<'ch>[src]

type Item = u8

impl<'ch> ParallelIterator for CharIndices<'ch>[src]

type Item = (usize, char)

impl<'ch> ParallelIterator for Chars<'ch>[src]

type Item = char

impl<'ch> ParallelIterator for EncodeUtf16<'ch>[src]

type Item = u16

impl<'ch> ParallelIterator for Lines<'ch>[src]

type Item = &'ch str

impl<'ch> ParallelIterator for SplitWhitespace<'ch>[src]

type Item = &'ch str

impl<'ch, P: Pattern> ParallelIterator for MatchIndices<'ch, P>[src]

type Item = (usize, &'ch str)

impl<'ch, P: Pattern> ParallelIterator for Matches<'ch, P>[src]

type Item = &'ch str

impl<'ch, P: Pattern> ParallelIterator for rayon::str::Split<'ch, P>[src]

type Item = &'ch str

impl<'ch, P: Pattern> ParallelIterator for SplitTerminator<'ch, P>[src]

type Item = &'ch str

impl<'data, T, P> ParallelIterator for rayon::slice::Split<'data, T, P> where
    P: Fn(&T) -> bool + Sync + Send,
    T: Sync, [src]

type Item = &'data [T]

impl<'data, T, P> ParallelIterator for SplitMut<'data, T, P> where
    P: Fn(&T) -> bool + Sync + Send,
    T: Send, [src]

type Item = &'data mut [T]

impl<'data, T: Send + 'data> ParallelIterator for ChunksMut<'data, T>[src]

type Item = &'data mut [T]

impl<'data, T: Send + 'data> ParallelIterator for rayon::slice::IterMut<'data, T>[src]

type Item = &'data mut T

impl<'data, T: Sync + 'data> ParallelIterator for rayon::slice::Chunks<'data, T>[src]

type Item = &'data [T]

impl<'data, T: Sync + 'data> ParallelIterator for rayon::slice::Iter<'data, T>[src]

type Item = &'data T

impl<'data, T: Sync + 'data> ParallelIterator for Windows<'data, T>[src]

type Item = &'data [T]

impl<A, B> ParallelIterator for Chain<A, B> where
    A: ParallelIterator,
    B: ParallelIterator<Item = A::Item>, [src]

type Item = A::Item

impl<A, B> ParallelIterator for Zip<A, B> where
    A: IndexedParallelIterator,
    B: IndexedParallelIterator, [src]

type Item = (A::Item, B::Item)

impl<A, B> ParallelIterator for ZipEq<A, B> where
    A: IndexedParallelIterator,
    B: IndexedParallelIterator, [src]

type Item = (A::Item, B::Item)

impl<D, S> ParallelIterator for rayon::iter::Split<D, S> where
    D: Send,
    S: Fn(D) -> (D, Option<D>) + Sync + Send, [src]

type Item = D

impl<I> ParallelIterator for rayon::iter::Chunks<I> where
    I: IndexedParallelIterator, [src]

type Item = Vec<I::Item>

impl<I> ParallelIterator for Enumerate<I> where
    I: IndexedParallelIterator, [src]

type Item = (usize, I::Item)

impl<I> ParallelIterator for Intersperse<I> where
    I: ParallelIterator,
    I::Item: Clone + Send, [src]

type Item = I::Item

impl<I> ParallelIterator for MaxLen<I> where
    I: IndexedParallelIterator, [src]

type Item = I::Item

impl<I> ParallelIterator for MinLen<I> where
    I: IndexedParallelIterator, [src]

type Item = I::Item

impl<I> ParallelIterator for PanicFuse<I> where
    I: ParallelIterator, [src]

type Item = I::Item

impl<I> ParallelIterator for Rev<I> where
    I: IndexedParallelIterator, [src]

type Item = I::Item

impl<I> ParallelIterator for Skip<I> where
    I: IndexedParallelIterator, [src]

type Item = I::Item

impl<I> ParallelIterator for Take<I> where
    I: IndexedParallelIterator, [src]

type Item = I::Item

impl<I, F> ParallelIterator for Inspect<I, F> where
    I: ParallelIterator,
    F: Fn(&I::Item) + Sync + Send, [src]

type Item = I::Item

impl<I, F> ParallelIterator for Update<I, F> where
    I: ParallelIterator,
    F: Fn(&mut I::Item) + Send + Sync, [src]

type Item = I::Item

impl<I, F, PI> ParallelIterator for FlatMap<I, F> where
    I: ParallelIterator,
    F: Fn(I::Item) -> PI + Sync + Send,
    PI: IntoParallelIterator, [src]

type Item = PI::Item

impl<I, F, R> ParallelIterator for Map<I, F> where
    I: ParallelIterator,
    F: Fn(I::Item) -> R + Sync + Send,
    R: Send, [src]

type Item = F::Output

impl<I, INIT, T, F, R> ParallelIterator for MapInit<I, INIT, F> where
    I: ParallelIterator,
    INIT: Fn() -> T + Sync + Send,
    F: Fn(&mut T, I::Item) -> R + Sync + Send,
    R: Send, [src]

type Item = R

impl<I, J> ParallelIterator for Interleave<I, J> where
    I: IndexedParallelIterator,
    J: IndexedParallelIterator<Item = I::Item>, [src]

type Item = I::Item

impl<I, J> ParallelIterator for InterleaveShortest<I, J> where
    I: IndexedParallelIterator,
    J: IndexedParallelIterator<Item = I::Item>, [src]

type Item = I::Item

impl<I, P> ParallelIterator for Filter<I, P> where
    I: ParallelIterator,
    P: Fn(&I::Item) -> bool + Sync + Send, [src]

type Item = I::Item

impl<I, P, R> ParallelIterator for FilterMap<I, P> where
    I: ParallelIterator,
    P: Fn(I::Item) -> Option<R> + Sync + Send,
    R: Send, [src]

type Item = R

impl<I, PI> ParallelIterator for Flatten<I> where
    I: ParallelIterator<Item = PI>,
    PI: IntoParallelIterator + Send, [src]

type Item = PI::Item

impl<I, T> ParallelIterator for WhileSome<I> where
    I: ParallelIterator<Item = Option<T>>,
    T: Send, [src]

type Item = T

impl<I, T, F, R> ParallelIterator for MapWith<I, T, F> where
    I: ParallelIterator,
    T: Send + Clone,
    F: Fn(&mut T, I::Item) -> R + Sync + Send,
    R: Send, [src]

type Item = R

impl<Iter: Iterator + Send> ParallelIterator for IterBridge<Iter> where
    Iter::Item: Send, [src]

type Item = Iter::Item

impl<K: Ord + Send, V: Send> ParallelIterator for rayon::collections::btree_map::IntoIter<K, V>[src]

type Item = (K, V)

impl<K: Hash + Eq + Send, V: Send> ParallelIterator for rayon::collections::hash_map::IntoIter<K, V>[src]

type Item = (K, V)

impl<L, R> ParallelIterator for Either<L, R> where
    L: ParallelIterator,
    R: ParallelIterator<Item = L::Item>, [src]

Either<L, R> is a parallel iterator if both L and R are parallel iterators.

type Item = L::Item

impl<T> ParallelIterator for Repeat<T> where
    T: Clone + Send, [src]

type Item = T

impl<T> ParallelIterator for RepeatN<T> where
    T: Clone + Send, [src]

type Item = T

impl<T: Ord + Send> ParallelIterator for rayon::collections::binary_heap::IntoIter<T>[src]

type Item = T

impl<T: Ord + Send> ParallelIterator for rayon::collections::btree_set::IntoIter<T>[src]

type Item = T

impl<T: Hash + Eq + Send> ParallelIterator for rayon::collections::hash_set::IntoIter<T>[src]

type Item = T

impl<T: Send> ParallelIterator for rayon::collections::linked_list::IntoIter<T>[src]

type Item = T

impl<T: Send> ParallelIterator for rayon::collections::vec_deque::IntoIter<T>[src]

type Item = T

impl<T: Send> ParallelIterator for Empty<T>[src]

type Item = T

impl<T: Send> ParallelIterator for Once<T>[src]

type Item = T

impl<T: Send> ParallelIterator for rayon::option::IntoIter<T>[src]

type Item = T

impl<T: Send> ParallelIterator for rayon::result::IntoIter<T>[src]

type Item = T

impl<T: Send> ParallelIterator for rayon::vec::IntoIter<T>[src]

type Item = T

impl<U, I, F> ParallelIterator for FoldWith<I, U, F> where
    I: ParallelIterator,
    F: Fn(U, I::Item) -> U + Sync + Send,
    U: Send + Clone, [src]

type Item = U

impl<U, I, F> ParallelIterator for TryFoldWith<I, U, F> where
    I: ParallelIterator,
    F: Fn(U::Ok, I::Item) -> U + Sync + Send,
    U: Try + Send,
    U::Ok: Clone + Send, [src]

type Item = U

impl<U, I, ID, F> ParallelIterator for Fold<I, ID, F> where
    I: ParallelIterator,
    F: Fn(U, I::Item) -> U + Sync + Send,
    ID: Fn() -> U + Sync + Send,
    U: Send, [src]

type Item = U

impl<U, I, ID, F> ParallelIterator for TryFold<I, U, ID, F> where
    I: ParallelIterator,
    F: Fn(U::Ok, I::Item) -> U + Sync + Send,
    ID: Fn() -> U::Ok + Sync + Send,
    U: Try + Send, [src]

type Item = U

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