Module iter 

Traits for writing parallel programs using an iterator-style interface

You will rarely need to interact with this module directly unless you have need to name one of the iterator types.

Parallel iterators make it easy to write iterator-like chains that execute in parallel: typically all you have to do is convert the first .iter() (or iter_mut(), into_iter(), etc) method into par_iter() (or par_iter_mut(), into_par_iter(), etc). For example, to compute the sum of the squares of a sequence of integers, one might write:

use rayon::prelude::*;
fn sum_of_squares(input: &[i32]) -> i32 {
    input.par_iter()
         .map(|i| i * i)
         .sum()
}

Or, to increment all the integers in a slice, you could write:

use rayon::prelude::*;
fn increment_all(input: &mut [i32]) {
    input.par_iter_mut()
         .for_each(|p| *p += 1);
}

To use parallel iterators, first import the traits by adding something like use rayon::prelude::* to your module. You can then call par_iter, par_iter_mut, or into_par_iter to get a parallel iterator. Like a regular iterator, parallel iterators work by first constructing a computation and then executing it.

In addition to par_iter() and friends, some types offer other ways to create (or consume) parallel iterators:

• Slices (&[T], &mut [T]) offer methods like par_split and par_windows, as well as various parallel sorting operations. See the ParallelSlice trait for the full list.
• Strings (&str) offer methods like par_split and par_lines. See the ParallelString trait for the full list.
• Various collections offer par_extend, which grows a collection given a parallel iterator. (If you don’t have a collection to extend, you can use collect() to create a new one from scratch.)

To see the full range of methods available on parallel iterators, check out the ParallelIterator and IndexedParallelIterator traits.

If you’d like to build a custom parallel iterator, or to write your own combinator, then check out the split function and the plumbing module.

Note: Several of the ParallelIterator methods rely on a Try trait which has been deliberately obscured from the public API. This trait is intended to mirror the unstable std::ops::Try with implementations for Option and Result, where Some/Ok values will let those iterators continue, but None/Err values will exit early.

A note about object safety: It is currently not possible to wrap a ParallelIterator (or any trait that depends on it) using a Box<dyn ParallelIterator> or other kind of dynamic allocation, because ParallelIterator is not object-safe. (This keeps the implementation simpler and allows extra optimizations.)

Modules

plumbing

Traits and functions used to implement parallel iteration. These are low-level details – users of parallel iterators should not need to interact with them directly. See the plumbing README for a general overview.

Structs

Chain

Chain is an iterator that joins b after a in one continuous iterator. This struct is created by the chain() method on ParallelIterator

Chunks

Chunks is an iterator that groups elements of an underlying iterator.

Cloned

Cloned is an iterator that clones the elements of an underlying iterator.

Copied

Copied is an iterator that copies the elements of an underlying iterator.

Empty

Iterator adaptor for the empty() function.

Enumerate

Enumerate is an iterator that returns the current count along with the element. This struct is created by the enumerate() method on IndexedParallelIterator

ExponentialBlocks

ExponentialBlocks is a parallel iterator that consumes itself as a sequence of parallel blocks of increasing sizes (exponentially).

Filter

Filter takes a predicate filter_op and filters out elements that match. This struct is created by the filter() method on ParallelIterator

FilterMap

FilterMap creates an iterator that uses filter_op to both filter and map elements. This struct is created by the filter_map() method on ParallelIterator.

FlatMap

FlatMap maps each element to a parallel iterator, then flattens these iterators together. This struct is created by the flat_map() method on ParallelIterator

FlatMapIter

FlatMapIter maps each element to a serial iterator, then flattens these iterators together. This struct is created by the flat_map_iter() method on ParallelIterator

Flatten

Flatten turns each element to a parallel iterator, then flattens these iterators together. This struct is created by the flatten() method on ParallelIterator.

FlattenIter

FlattenIter turns each element to a serial iterator, then flattens these iterators together. This struct is created by the flatten_iter() method on ParallelIterator.

Fold

Fold is an iterator that applies a function over an iterator producing a single value. This struct is created by the fold() method on ParallelIterator

FoldChunks

FoldChunks is an iterator that groups elements of an underlying iterator and applies a function over them, producing a single value for each group.

FoldChunksWith

FoldChunksWith is an iterator that groups elements of an underlying iterator and applies a function over them, producing a single value for each group.

FoldWith

FoldWith is an iterator that applies a function over an iterator producing a single value. This struct is created by the fold_with() method on ParallelIterator

Inspect

Inspect is an iterator that calls a function with a reference to each element before yielding it.

Interleave

Interleave is an iterator that interleaves elements of iterators i and j in one continuous iterator. This struct is created by the interleave() method on IndexedParallelIterator

InterleaveShortest

InterleaveShortest is an iterator that works similarly to Interleave, but this version stops returning elements once one of the iterators run out.

Intersperse

Intersperse is an iterator that inserts a particular item between each item of the adapted iterator. This struct is created by the intersperse() method on ParallelIterator

IterBridge

IterBridge is a parallel iterator that wraps a sequential iterator.

Map

Map is an iterator that transforms the elements of an underlying iterator.

MapInit

MapInit is an iterator that transforms the elements of an underlying iterator.

MapWith

MapWith is an iterator that transforms the elements of an underlying iterator.

MaxLen

MaxLen is an iterator that imposes a maximum length on iterator splits. This struct is created by the with_max_len() method on IndexedParallelIterator

MinLen

MinLen is an iterator that imposes a minimum length on iterator splits. This struct is created by the with_min_len() method on IndexedParallelIterator

MultiZip

MultiZip is an iterator that zips up a tuple of parallel iterators to produce tuples of their items.

Once

Iterator adaptor for the once() function.

PanicFuse

PanicFuse is an adaptor that wraps an iterator with a fuse in case of panics, to halt all threads as soon as possible.

Positions

Positions takes a predicate predicate and filters out elements that match, yielding their indices.

Repeat

Iterator adaptor for the repeat() function.

RepeatN

Iterator adaptor for the repeatn() function.

Rev

Rev is an iterator that produces elements in reverse order. This struct is created by the rev() method on IndexedParallelIterator

Skip

Skip is an iterator that skips over the first n elements. This struct is created by the skip() method on IndexedParallelIterator

SkipAny

SkipAny is an iterator that skips over n elements from anywhere in I. This struct is created by the skip_any() method on ParallelIterator

SkipAnyWhile

SkipAnyWhile is an iterator that skips over elements from anywhere in I until the callback returns false. This struct is created by the skip_any_while() method on ParallelIterator

Split

Split is a parallel iterator using arbitrary data and a splitting function. This struct is created by the split() function.

StepBy

StepBy is an iterator that skips n elements between each yield, where n is the given step. This struct is created by the step_by() method on IndexedParallelIterator

Take

Take is an iterator that iterates over the first n elements. This struct is created by the take() method on IndexedParallelIterator

TakeAny

TakeAny is an iterator that iterates over n elements from anywhere in I. This struct is created by the take_any() method on ParallelIterator

TakeAnyWhile

TakeAnyWhile is an iterator that iterates over elements from anywhere in I until the callback returns false. This struct is created by the take_any_while() method on ParallelIterator

TryFold

TryFold is an iterator that applies a function over an iterator producing a single value. This struct is created by the try_fold() method on ParallelIterator

TryFoldWith

TryFoldWith is an iterator that applies a function over an iterator producing a single value. This struct is created by the try_fold_with() method on ParallelIterator

UniformBlocks

UniformBlocks is a parallel iterator that consumes itself as a sequence of parallel blocks of constant sizes.

Update

Update is an iterator that mutates the elements of an underlying iterator before they are yielded.

WalkTree

ParallelIterator for arbitrary tree-shaped patterns. Returned by the walk_tree() function.

WalkTreePostfix

ParallelIterator for arbitrary tree-shaped patterns. Returned by the walk_tree_postfix() function.

WalkTreePrefix

ParallelIterator for arbitrary tree-shaped patterns. Returned by the walk_tree_prefix() function.

WhileSome

WhileSome is an iterator that yields the Some elements of an iterator, halting as soon as any None is produced.

Zip

Zip is an iterator that zips up a and b into a single iterator of pairs. This struct is created by the zip() method on IndexedParallelIterator

ZipEq

An IndexedParallelIterator that iterates over two parallel iterators of equal length simultaneously.

Enums

Either

The enum Either with variants Left and Right is a general purpose sum type with two cases.

Traits

FromParallelIterator

FromParallelIterator implements the creation of a collection from a ParallelIterator. By implementing FromParallelIterator for a given type, you define how it will be created from an iterator.

IndexedParallelIterator

An iterator that supports “random access” to its data, meaning that you can split it at arbitrary indices and draw data from those points.

IntoParallelIterator

IntoParallelIterator implements the conversion to a ParallelIterator.

IntoParallelRefIterator

IntoParallelRefIterator implements the conversion to a ParallelIterator, providing shared references to the data.

IntoParallelRefMutIterator

IntoParallelRefMutIterator implements the conversion to a ParallelIterator, providing mutable references to the data.

ParallelBridge

Conversion trait to convert an Iterator to a ParallelIterator.

ParallelDrainFull

ParallelDrainFull creates a parallel iterator that moves all items from a collection while retaining the original capacity.

ParallelDrainRange

ParallelDrainRange creates a parallel iterator that moves a range of items from a collection while retaining the original capacity.

ParallelExtend

ParallelExtend extends an existing collection with items from a ParallelIterator.

ParallelIterator

Parallel version of the standard iterator trait.

Functions

empty

Creates a parallel iterator that produces nothing.

once

Creates a parallel iterator that produces an element exactly once.

repeat

Creates a parallel iterator that endlessly repeats elt (by cloning it). Note that this iterator has “infinite” length, so typically you would want to use zip or take or some other means to shorten it, or consider using the repeatn() function instead.

repeatn

Creates a parallel iterator that produces n repeats of elt (by cloning it).

split

The split function takes arbitrary data and a closure that knows how to split it, and turns this into a ParallelIterator.

walk_tree

Create a tree like parallel iterator from an initial root node. The children_of function should take a node and iterate on all of its child nodes. The best parallelization is obtained when the tree is balanced but we should also be able to handle harder cases.

walk_tree_postfix

Create a tree like postfix parallel iterator from an initial root node. The children_of function should take a node and iterate on all of its child nodes. The best parallelization is obtained when the tree is balanced but we should also be able to handle harder cases.

walk_tree_prefix

Create a tree-like prefix parallel iterator from an initial root node. The children_of function should take a node and return an iterator over its child nodes. The best parallelization is obtained when the tree is balanced but we should also be able to handle harder cases.