//! 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:
//!
//! ```rust
//! 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:
//!
//! ```rust
//! 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.)
//!
//! [the `ParallelSlice` trait]: ../slice/trait.ParallelSlice.html
//! [the `ParallelString` trait]: ../str/trait.ParallelString.html
//! [`par_extend`]: trait.ParallelExtend.html
//! [`collect()`]: trait.ParallelIterator.html#method.collect
//!
//! 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.
//!
//! [regular iterator]: https://doc.rust-lang.org/std/iter/trait.Iterator.html
//! [`ParallelIterator`]: trait.ParallelIterator.html
//! [`IndexedParallelIterator`]: trait.IndexedParallelIterator.html
//! [split]: fn.split.html
//! [plumbing]: plumbing/index.html
//!
//! 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.)
use self::plumbing::*;
use self::private::Try;
pub use either::Either;
use std::cmp::{self, Ordering};
use std::iter::{Product, Sum};
use std::ops::{Fn, RangeBounds};
pub mod plumbing;
#[cfg(test)]
mod test;
// There is a method to the madness here:
//
// - These modules are private but expose certain types to the end-user
// (e.g., `enumerate::Enumerate`) -- specifically, the types that appear in the
// public API surface of the `ParallelIterator` traits.
// - In **this** module, those public types are always used unprefixed, which forces
// us to add a `pub use` and helps identify if we missed anything.
// - In contrast, items that appear **only** in the body of a method,
// e.g. `find::find()`, are always used **prefixed**, so that they
// can be readily distinguished.
mod chain;
mod chunks;
mod cloned;
mod collect;
mod copied;
mod empty;
mod enumerate;
mod extend;
mod filter;
mod filter_map;
mod find;
mod find_first_last;
mod flat_map;
mod flat_map_iter;
mod flatten;
mod flatten_iter;
mod fold;
mod fold_chunks;
mod fold_chunks_with;
mod for_each;
mod from_par_iter;
mod inspect;
mod interleave;
mod interleave_shortest;
mod intersperse;
mod len;
mod map;
mod map_with;
mod multizip;
mod noop;
mod once;
mod panic_fuse;
mod par_bridge;
mod positions;
mod product;
mod reduce;
mod repeat;
mod rev;
mod skip;
mod splitter;
mod step_by;
mod sum;
mod take;
mod try_fold;
mod try_reduce;
mod try_reduce_with;
mod unzip;
mod update;
mod while_some;
mod zip;
mod zip_eq;
pub use self::{
chain::Chain,
chunks::Chunks,
cloned::Cloned,
copied::Copied,
empty::{empty, Empty},
enumerate::Enumerate,
filter::Filter,
filter_map::FilterMap,
flat_map::FlatMap,
flat_map_iter::FlatMapIter,
flatten::Flatten,
flatten_iter::FlattenIter,
fold::{Fold, FoldWith},
fold_chunks::FoldChunks,
fold_chunks_with::FoldChunksWith,
inspect::Inspect,
interleave::Interleave,
interleave_shortest::InterleaveShortest,
intersperse::Intersperse,
len::{MaxLen, MinLen},
map::Map,
map_with::{MapInit, MapWith},
multizip::MultiZip,
once::{once, Once},
panic_fuse::PanicFuse,
par_bridge::{IterBridge, ParallelBridge},
positions::Positions,
repeat::{repeat, repeatn, Repeat, RepeatN},
rev::Rev,
skip::Skip,
splitter::{split, Split},
step_by::StepBy,
take::Take,
try_fold::{TryFold, TryFoldWith},
update::Update,
while_some::WhileSome,
zip::Zip,
zip_eq::ZipEq,
};
/// `IntoParallelIterator` implements the conversion to a [`ParallelIterator`].
///
/// By implementing `IntoParallelIterator` for a type, you define how it will
/// transformed into an iterator. This is a parallel version of the standard
/// library's [`std::iter::IntoIterator`] trait.
///
/// [`ParallelIterator`]: trait.ParallelIterator.html
/// [`std::iter::IntoIterator`]: https://doc.rust-lang.org/std/iter/trait.IntoIterator.html
pub trait IntoParallelIterator {
/// The parallel iterator type that will be created.
type Iter: ParallelIterator<Item = Self::Item>;
/// The type of item that the parallel iterator will produce.
type Item: Send;
/// Converts `self` into a parallel iterator.
///
/// # Examples
///
/// ```
/// use rayon::prelude::*;
///
/// println!("counting in parallel:");
/// (0..100).into_par_iter()
/// .for_each(|i| println!("{}", i));
/// ```
///
/// This conversion is often implicit for arguments to methods like [`zip`].
///
/// ```
/// use rayon::prelude::*;
///
/// let v: Vec<_> = (0..5).into_par_iter().zip(5..10).collect();
/// assert_eq!(v, [(0, 5), (1, 6), (2, 7), (3, 8), (4, 9)]);
/// ```
///
/// [`zip`]: trait.IndexedParallelIterator.html#method.zip
fn into_par_iter(self) -> Self::Iter;
}
/// `IntoParallelRefIterator` implements the conversion to a
/// [`ParallelIterator`], providing shared references to the data.
///
/// This is a parallel version of the `iter()` method
/// defined by various collections.
///
/// This trait is automatically implemented
/// `for I where &I: IntoParallelIterator`. In most cases, users
/// will want to implement [`IntoParallelIterator`] rather than implement
/// this trait directly.
///
/// [`ParallelIterator`]: trait.ParallelIterator.html
/// [`IntoParallelIterator`]: trait.IntoParallelIterator.html
pub trait IntoParallelRefIterator<'data> {
/// The type of the parallel iterator that will be returned.
type Iter: ParallelIterator<Item = Self::Item>;
/// The type of item that the parallel iterator will produce.
/// This will typically be an `&'data T` reference type.
type Item: Send + 'data;
/// Converts `self` into a parallel iterator.
///
/// # Examples
///
/// ```
/// use rayon::prelude::*;
///
/// let v: Vec<_> = (0..100).collect();
/// assert_eq!(v.par_iter().sum::<i32>(), 100 * 99 / 2);
///
/// // `v.par_iter()` is shorthand for `(&v).into_par_iter()`,
/// // producing the exact same references.
/// assert!(v.par_iter().zip(&v)
/// .all(|(a, b)| std::ptr::eq(a, b)));
/// ```
fn par_iter(&'data self) -> Self::Iter;
}
impl<'data, I: 'data + ?Sized> IntoParallelRefIterator<'data> for I
where
&'data I: IntoParallelIterator,
{
type Iter = <&'data I as IntoParallelIterator>::Iter;
type Item = <&'data I as IntoParallelIterator>::Item;
fn par_iter(&'data self) -> Self::Iter {
self.into_par_iter()
}
}
/// `IntoParallelRefMutIterator` implements the conversion to a
/// [`ParallelIterator`], providing mutable references to the data.
///
/// This is a parallel version of the `iter_mut()` method
/// defined by various collections.
///
/// This trait is automatically implemented
/// `for I where &mut I: IntoParallelIterator`. In most cases, users
/// will want to implement [`IntoParallelIterator`] rather than implement
/// this trait directly.
///
/// [`ParallelIterator`]: trait.ParallelIterator.html
/// [`IntoParallelIterator`]: trait.IntoParallelIterator.html
pub trait IntoParallelRefMutIterator<'data> {
/// The type of iterator that will be created.
type Iter: ParallelIterator<Item = Self::Item>;
/// The type of item that will be produced; this is typically an
/// `&'data mut T` reference.
type Item: Send + 'data;
/// Creates the parallel iterator from `self`.
///
/// # Examples
///
/// ```
/// use rayon::prelude::*;
///
/// let mut v = vec![0usize; 5];
/// v.par_iter_mut().enumerate().for_each(|(i, x)| *x = i);
/// assert_eq!(v, [0, 1, 2, 3, 4]);
/// ```
fn par_iter_mut(&'data mut self) -> Self::Iter;
}
impl<'data, I: 'data + ?Sized> IntoParallelRefMutIterator<'data> for I
where
&'data mut I: IntoParallelIterator,
{
type Iter = <&'data mut I as IntoParallelIterator>::Iter;
type Item = <&'data mut I as IntoParallelIterator>::Item;
fn par_iter_mut(&'data mut self) -> Self::Iter {
self.into_par_iter()
}
}
/// 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][iter].
///
/// [iter]: index.html
/// [`IndexedParallelIterator`]: trait.IndexedParallelIterator.html
pub trait ParallelIterator: Sized + 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.
///
/// [`for_each`]: #method.for_each
type Item: 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<OP>(self, op: OP)
where
OP: Fn(Self::Item) + Sync + Send,
{
for_each::for_each(self, &op)
}
/// 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_with<OP, T>(self, init: T, op: OP)
where
OP: Fn(&mut T, Self::Item) + Sync + Send,
T: Send + Clone,
{
self.map_with(init, op).collect()
}
/// 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
///
/// ```
/// 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 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,
{
self.map_init(init, op).collect()
}
/// 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<OP, R>(self, op: OP) -> R
where
OP: Fn(Self::Item) -> R + Sync + Send,
R: Try<Output = ()> + Send,
{
fn ok<R: Try<Output = ()>>(_: (), _: ()) -> R {
R::from_output(())
}
self.map(op).try_reduce(<()>::default, ok)
}
/// 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()`].
///
/// [`for_each_with()`]: #method.for_each_with
/// [`try_for_each()`]: #method.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_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<Output = ()> + Send,
{
fn ok<R: Try<Output = ()>>(_: (), _: ()) -> R {
R::from_output(())
}
self.map_with(init, op).try_reduce(<()>::default, ok)
}
/// 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()`].
///
/// [`for_each_init()`]: #method.for_each_init
/// [`try_for_each()`]: #method.try_for_each
///
/// # Examples
///
/// ```
/// 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 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<Output = ()> + Send,
{
fn ok<R: Try<Output = ()>>(_: (), _: ()) -> R {
R::from_output(())
}
self.map_init(init, op).try_reduce(<()>::default, ok)
}
/// 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 count(self) -> usize {
fn one<T>(_: T) -> usize {
1
}
self.map(one).sum()
}
/// 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<F, R>(self, map_op: F) -> Map<Self, F>
where
F: Fn(Self::Item) -> R + Sync + Send,
R: Send,
{
Map::new(self, map_op)
}
/// 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_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,
{
MapWith::new(self, init, map_op)
}
/// 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
///
/// ```
/// 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 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,
{
MapInit::new(self, init, map_op)
}
/// 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()`].
///
/// [`copied()`]: #method.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 cloned<'a, T>(self) -> Cloned<Self>
where
T: 'a + Clone + Send,
Self: ParallelIterator<Item = &'a T>,
{
Cloned::new(self)
}
/// 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()`].
///
/// [`cloned()`]: #method.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 copied<'a, T>(self) -> Copied<Self>
where
T: 'a + Copy + Send,
Self: ParallelIterator<Item = &'a T>,
{
Copied::new(self)
}
/// 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 inspect<OP>(self, inspect_op: OP) -> Inspect<Self, OP>
where
OP: Fn(&Self::Item) + Sync + Send,
{
Inspect::new(self, inspect_op)
}
/// 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 update<F>(self, update_op: F) -> Update<Self, F>
where
F: Fn(&mut Self::Item) + Sync + Send,
{
Update::new(self, update_op)
}
/// 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<P>(self, filter_op: P) -> Filter<Self, P>
where
P: Fn(&Self::Item) -> bool + Sync + Send,
{
Filter::new(self, filter_op)
}
/// 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 filter_map<P, R>(self, filter_op: P) -> FilterMap<Self, P>
where
P: Fn(Self::Item) -> Option<R> + Sync + Send,
R: Send,
{
FilterMap::new(self, filter_op)
}
/// Applies `map_op` to each item of this iterator to get nested parallel iterators,
/// producing a new parallel iterator that flattens these back into one.
///
/// See also [`flat_map_iter`](#method.flat_map_iter).
///
/// # 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 flat_map<F, PI>(self, map_op: F) -> FlatMap<Self, F>
where
F: Fn(Self::Item) -> PI + Sync + Send,
PI: IntoParallelIterator,
{
FlatMap::new(self, map_op)
}
/// Applies `map_op` to each item of this iterator to get nested serial iterators,
/// producing a new parallel iterator that flattens these back into one.
///
/// # `flat_map_iter` versus `flat_map`
///
/// These two methods are similar but behave slightly differently. With [`flat_map`],
/// each of the nested iterators must be a parallel iterator, and they will be further
/// split up with nested parallelism. With `flat_map_iter`, each nested iterator is a
/// sequential `Iterator`, and we only parallelize _between_ them, while the items
/// produced by each nested iterator are processed sequentially.
///
/// When choosing between these methods, consider whether nested parallelism suits the
/// potential iterators at hand. If there's little computation involved, or its length
/// is much less than the outer parallel iterator, then it may perform better to avoid
/// the overhead of parallelism, just flattening sequentially with `flat_map_iter`.
/// If there is a lot of computation, potentially outweighing the outer parallel
/// iterator, then the nested parallelism of `flat_map` may be worthwhile.
///
/// [`flat_map`]: #method.flat_map
///
/// # Examples
///
/// ```
/// use rayon::prelude::*;
/// use std::cell::RefCell;
///
/// let a = [[1, 2], [3, 4], [5, 6], [7, 8]];
///
/// let par_iter = a.par_iter().flat_map_iter(|a| {
/// // The serial iterator doesn't have to be thread-safe, just its items.
/// let cell_iter = RefCell::new(a.iter().cloned());
/// std::iter::from_fn(move || cell_iter.borrow_mut().next())
/// });
///
/// let vec: Vec<_> = par_iter.collect();
///
/// assert_eq!(&vec[..], &[1, 2, 3, 4, 5, 6, 7, 8]);
/// ```
fn flat_map_iter<F, SI>(self, map_op: F) -> FlatMapIter<Self, F>
where
F: Fn(Self::Item) -> SI + Sync + Send,
SI: IntoIterator,
SI::Item: Send,
{
FlatMapIter::new(self, map_op)
}
/// An adaptor that flattens parallel-iterable `Item`s into one large iterator.
///
/// See also [`flatten_iter`](#method.flatten_iter).
///
/// # 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 flatten(self) -> Flatten<Self>
where
Self::Item: IntoParallelIterator,
{
Flatten::new(self)
}
/// An adaptor that flattens serial-iterable `Item`s into one large iterator.
///
/// See also [`flatten`](#method.flatten) and the analogous comparison of
/// [`flat_map_iter` versus `flat_map`](#flat_map_iter-versus-flat_map).
///
/// # Examples
///
/// ```
/// use rayon::prelude::*;
///
/// let x: Vec<Vec<_>> = vec![vec![1, 2], vec![3, 4]];
/// let iters: Vec<_> = x.into_iter().map(Vec::into_iter).collect();
/// let y: Vec<_> = iters.into_par_iter().flatten_iter().collect();
///
/// assert_eq!(y, vec![1, 2, 3, 4]);
/// ```
fn flatten_iter(self) -> FlattenIter<Self>
where
Self::Item: IntoIterator,
<Self::Item as IntoIterator>::Item: Send,
{
FlattenIter::new(self)
}
/// 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.
///
/// [associative]: https://en.wikipedia.org/wiki/Associative_property
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,
{
reduce::reduce(self, identity, op)
}
/// 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.
///
/// [associative]: https://en.wikipedia.org/wiki/Associative_property
fn reduce_with<OP>(self, op: OP) -> Option<Self::Item>
where
OP: Fn(Self::Item, Self::Item) -> Self::Item + Sync + Send,
{
fn opt_fold<T>(op: impl Fn(T, T) -> T) -> impl Fn(Option<T>, T) -> Option<T> {
move |opt_a, b| match opt_a {
Some(a) => Some(op(a, b)),
None => Some(b),
}
}
fn opt_reduce<T>(op: impl Fn(T, T) -> T) -> impl Fn(Option<T>, Option<T>) -> Option<T> {
move |opt_a, opt_b| match (opt_a, opt_b) {
(Some(a), Some(b)) => Some(op(a, b)),
(Some(v), None) | (None, Some(v)) => Some(v),
(None, None) => None,
}
}
self.fold(<_>::default, opt_fold(&op))
.reduce(<_>::default, opt_reduce(&op))
}
/// Reduces the items in the iterator into one item using a fallible `op`.
/// The `identity` argument is used the same way as in [`reduce()`].
///
/// [`reduce()`]: #method.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<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<Output = T>,
{
try_reduce::try_reduce(self, identity, op)
}
/// 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`.
///
/// [`reduce_with()`]: #method.reduce_with
/// [`try_reduce()`]: #method.try_reduce
///
/// 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 try_reduce_with<T, OP>(self, op: OP) -> Option<Self::Item>
where
OP: Fn(T, T) -> Self::Item + Sync + Send,
Self::Item: Try<Output = T>,
{
try_reduce_with::try_reduce_with(self, op)
}
/// 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 we 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:
///
/// ```notrust
/// 22 3 77 89 46
/// | |
/// 102 135
/// ```
///
/// Or perhaps these three numbers:
///
/// ```notrust
/// 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<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,
{
Fold::new(self, identity, fold_op)
}
/// 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 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,
{
FoldWith::new(self, init, fold_op)
}
/// Performs 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.
///
/// [`fold()`]: #method.fold
/// [`try_reduce()`]: #method.try_reduce
///
/// # 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<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<Output = T> + Send,
{
TryFold::new(self, identity, fold_op)
}
/// Performs a fallible parallel fold with a cloneable `init` value.
///
/// This combines the `init` semantics of [`fold_with()`] and the failure
/// semantics of [`try_fold()`].
///
/// [`fold_with()`]: #method.fold_with
/// [`try_fold()`]: #method.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 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<Output = T> + Send,
T: Clone + Send,
{
TryFoldWith::new(self, init, fold_op)
}
/// 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.
///
/// [associative]: https://en.wikipedia.org/wiki/Associative_property
///
/// 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 sum<S>(self) -> S
where
S: Send + Sum<Self::Item> + Sum<S>,
{
sum::sum(self)
}
/// 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.
///
/// [associative]: https://en.wikipedia.org/wiki/Associative_property
///
/// 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 product<P>(self) -> P
where
P: Send + Product<Self::Item> + Product<P>,
{
product::product(self)
}
/// 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(self) -> Option<Self::Item>
where
Self::Item: Ord,
{
self.reduce_with(cmp::min)
}
/// 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<F>(self, f: F) -> Option<Self::Item>
where
F: Sync + Send + Fn(&Self::Item, &Self::Item) -> Ordering,
{
fn min<T>(f: impl Fn(&T, &T) -> Ordering) -> impl Fn(T, T) -> T {
move |a, b| match f(&a, &b) {
Ordering::Greater => b,
_ => a,
}
}
self.reduce_with(min(f))
}
/// 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 min_by_key<K, F>(self, f: F) -> Option<Self::Item>
where
K: Ord + Send,
F: Sync + Send + Fn(&Self::Item) -> K,
{
fn key<T, K>(f: impl Fn(&T) -> K) -> impl Fn(T) -> (K, T) {
move |x| (f(&x), x)
}
fn min_key<T, K: Ord>(a: (K, T), b: (K, T)) -> (K, T) {
match (a.0).cmp(&b.0) {
Ordering::Greater => b,
_ => a,
}
}
let (_, x) = self.map(key(f)).reduce_with(min_key)?;
Some(x)
}
/// 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(self) -> Option<Self::Item>
where
Self::Item: Ord,
{
self.reduce_with(cmp::max)
}
/// 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<F>(self, f: F) -> Option<Self::Item>
where
F: Sync + Send + Fn(&Self::Item, &Self::Item) -> Ordering,
{
fn max<T>(f: impl Fn(&T, &T) -> Ordering) -> impl Fn(T, T) -> T {
move |a, b| match f(&a, &b) {
Ordering::Greater => a,
_ => b,
}
}
self.reduce_with(max(f))
}
/// 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 max_by_key<K, F>(self, f: F) -> Option<Self::Item>
where
K: Ord + Send,
F: Sync + Send + Fn(&Self::Item) -> K,
{
fn key<T, K>(f: impl Fn(&T) -> K) -> impl Fn(T) -> (K, T) {
move |x| (f(&x), x)
}
fn max_key<T, K: Ord>(a: (K, T), b: (K, T)) -> (K, T) {
match (a.0).cmp(&b.0) {
Ordering::Greater => a,
_ => b,
}
}
let (_, x) = self.map(key(f)).reduce_with(max_key)?;
Some(x)
}
/// 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 chain<C>(self, chain: C) -> Chain<Self, C::Iter>
where
C: IntoParallelIterator<Item = Self::Item>,
{
Chain::new(self, chain.into_par_iter())
}
/// 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][find] 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).
///
/// [find]: https://doc.rust-lang.org/std/iter/trait.Iterator.html#method.find
///
/// # 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_any<P>(self, predicate: P) -> Option<Self::Item>
where
P: Fn(&Self::Item) -> bool + Sync + Send,
{
find::find(self, predicate)
}
/// 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_first<P>(self, predicate: P) -> Option<Self::Item>
where
P: Fn(&Self::Item) -> bool + Sync + Send,
{
find_first_last::find_first(self, predicate)
}
/// 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_last<P>(self, predicate: P) -> Option<Self::Item>
where
P: Fn(&Self::Item) -> bool + Sync + Send,
{
find_first_last::find_last(self, predicate)
}
/// 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 found_number = c.par_iter().find_map_any(|s| s.parse().ok());
///
/// assert_eq!(found_number, Some(5));
/// ```
fn find_map_any<P, R>(self, predicate: P) -> Option<R>
where
P: Fn(Self::Item) -> Option<R> + Sync + Send,
R: Send,
{
fn yes<T>(_: &T) -> bool {
true
}
self.filter_map(predicate).find_any(yes)
}
/// 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_first<P, R>(self, predicate: P) -> Option<R>
where
P: Fn(Self::Item) -> Option<R> + Sync + Send,
R: Send,
{
fn yes<T>(_: &T) -> bool {
true
}
self.filter_map(predicate).find_first(yes)
}
/// 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 last_number = c.par_iter().find_map_last(|s| s.parse().ok());
///
/// assert_eq!(last_number, Some(5));
/// ```
fn find_map_last<P, R>(self, predicate: P) -> Option<R>
where
P: Fn(Self::Item) -> Option<R> + Sync + Send,
R: Send,
{
fn yes<T>(_: &T) -> bool {
true
}
self.filter_map(predicate).find_last(yes)
}
#[doc(hidden)]
#[deprecated(note = "parallel `find` does not search in order -- use `find_any`, \\
`find_first`, or `find_last`")]
fn find<P>(self, predicate: P) -> Option<Self::Item>
where
P: Fn(&Self::Item) -> bool + Sync + Send,
{
self.find_any(predicate)
}
/// 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 any<P>(self, predicate: P) -> bool
where
P: Fn(Self::Item) -> bool + Sync + Send,
{
self.map(predicate).find_any(bool::clone).is_some()
}
/// 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 all<P>(self, predicate: P) -> bool
where
P: Fn(Self::Item) -> bool + Sync + Send,
{
#[inline]
fn is_false(x: &bool) -> bool {
!x
}
self.map(predicate).find_any(is_false).is_none()
}
/// 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 while_some<T>(self) -> WhileSome<Self>
where
Self: ParallelIterator<Item = Option<T>>,
T: Send,
{
WhileSome::new(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.
///
/// [`join`]: ../fn.join.html#panics
///
/// # 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.
///
/// ```should_panic
/// 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 panic_fuse(self) -> PanicFuse<Self> {
PanicFuse::new(self)
}
/// Creates a fresh collection containing all the elements produced
/// by this parallel iterator.
///
/// You may prefer [`collect_into_vec()`] implemented on
/// [`IndexedParallelIterator`], if your underlying iterator also implements
/// it. [`collect_into_vec()`] allocates 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.
///
/// [`IndexedParallelIterator`]: trait.IndexedParallelIterator.html
/// [`collect_into_vec()`]:
/// trait.IndexedParallelIterator.html#method.collect_into_vec
///
/// # 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);
/// ```
///
/// You can collect a pair of collections like [`unzip`](#method.unzip)
/// for paired items:
///
/// ```
/// use rayon::prelude::*;
///
/// let a = [(0, 1), (1, 2), (2, 3), (3, 4)];
/// let (first, second): (Vec<_>, Vec<_>) = a.into_par_iter().collect();
///
/// assert_eq!(first, [0, 1, 2, 3]);
/// assert_eq!(second, [1, 2, 3, 4]);
/// ```
///
/// Or like [`partition_map`](#method.partition_map) for `Either` items:
///
/// ```
/// use rayon::prelude::*;
/// use rayon::iter::Either;
///
/// let (left, right): (Vec<_>, Vec<_>) = (0..8).into_par_iter().map(|x| {
/// if x % 2 == 0 {
/// Either::Left(x * 4)
/// } else {
/// Either::Right(x * 3)
/// }
/// }).collect();
///
/// assert_eq!(left, [0, 8, 16, 24]);
/// assert_eq!(right, [3, 9, 15, 21]);
/// ```
///
/// You can even collect an arbitrarily-nested combination of pairs and `Either`:
///
/// ```
/// use rayon::prelude::*;
/// use rayon::iter::Either;
///
/// let (first, (left, right)): (Vec<_>, (Vec<_>, Vec<_>))
/// = (0..8).into_par_iter().map(|x| {
/// if x % 2 == 0 {
/// (x, Either::Left(x * 4))
/// } else {
/// (-x, Either::Right(x * 3))
/// }
/// }).collect();
///
/// assert_eq!(first, [0, -1, 2, -3, 4, -5, 6, -7]);
/// assert_eq!(left, [0, 8, 16, 24]);
/// assert_eq!(right, [3, 9, 15, 21]);
/// ```
///
/// All of that can _also_ be combined with short-circuiting collection of
/// `Result` or `Option` types:
///
/// ```
/// use rayon::prelude::*;
/// use rayon::iter::Either;
///
/// let result: Result<(Vec<_>, (Vec<_>, Vec<_>)), _>
/// = (0..8).into_par_iter().map(|x| {
/// if x > 5 {
/// Err(x)
/// } else if x % 2 == 0 {
/// Ok((x, Either::Left(x * 4)))
/// } else {
/// Ok((-x, Either::Right(x * 3)))
/// }
/// }).collect();
///
/// let error = result.unwrap_err();
/// assert!(error == 6 || error == 7);
/// ```
fn collect<C>(self) -> C
where
C: FromParallelIterator<Self::Item>,
{
C::from_par_iter(self)
}
/// 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 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,
{
unzip::unzip(self)
}
/// 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 inference 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<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,
{
unzip::partition(self, predicate)
}
/// 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 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,
{
unzip::partition_map(self, predicate)
}
/// 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 intersperse(self, element: Self::Item) -> Intersperse<Self>
where
Self::Item: Clone,
{
Intersperse::new(self, element)
}
/// 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.
///
/// [README]: https://github.com/rayon-rs/rayon/blob/master/src/iter/plumbing/README.md
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.
///
/// 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.
fn opt_len(&self) -> Option<usize> {
None
}
}
impl<T: ParallelIterator> IntoParallelIterator for T {
type Iter = T;
type Item = T::Item;
fn into_par_iter(self) -> T {
self
}
}
/// An iterator that supports "random access" to its data, meaning
/// that you can split it at arbitrary indices and draw data from
/// those points.
///
/// **Note:** Not implemented for `u64`, `i64`, `u128`, or `i128` ranges
// Waiting for `ExactSizeIterator::is_empty` to be stabilized. See rust-lang/rust#35428
#[allow(clippy::len_without_is_empty)]
pub trait IndexedParallelIterator: ParallelIterator {
/// Collects the results of the iterator into the specified
/// vector. The vector is always truncated before execution
/// begins. If possible, reusing the vector across calls can lead
/// to better performance since it reuses the same backing buffer.
///
/// # Examples
///
/// ```
/// use rayon::prelude::*;
///
/// // any prior data will be truncated
/// let mut vec = vec![-1, -2, -3];
///
/// (0..5).into_par_iter()
/// .collect_into_vec(&mut vec);
///
/// assert_eq!(vec, [0, 1, 2, 3, 4]);
/// ```
fn collect_into_vec(self, target: &mut Vec<Self::Item>) {
collect::collect_into_vec(self, target);
}
/// Unzips the results of the iterator into the specified
/// vectors. The vectors are always truncated before execution
/// begins. If possible, reusing the vectors across calls can lead
/// to better performance since they reuse the same backing buffer.
///
/// # Examples
///
/// ```
/// use rayon::prelude::*;
///
/// // any prior data will be truncated
/// let mut left = vec![42; 10];
/// let mut right = vec![-1; 10];
///
/// (10..15).into_par_iter()
/// .enumerate()
/// .unzip_into_vecs(&mut left, &mut right);
///
/// assert_eq!(left, [0, 1, 2, 3, 4]);
/// assert_eq!(right, [10, 11, 12, 13, 14]);
/// ```
fn unzip_into_vecs<A, B>(self, left: &mut Vec<A>, right: &mut Vec<B>)
where
Self: IndexedParallelIterator<Item = (A, B)>,
A: Send,
B: Send,
{
collect::unzip_into_vecs(self, left, right);
}
/// Iterates over tuples `(A, B)`, where the items `A` are from
/// this iterator and `B` are from the iterator given as argument.
/// Like the `zip` method on ordinary iterators, if the two
/// iterators are of unequal length, you only get the items they
/// have in common.
///
/// # Examples
///
/// ```
/// use rayon::prelude::*;
///
/// let result: Vec<_> = (1..4)
/// .into_par_iter()
/// .zip(vec!['a', 'b', 'c'])
/// .collect();
///
/// assert_eq!(result, [(1, 'a'), (2, 'b'), (3, 'c')]);
/// ```
fn zip<Z>(self, zip_op: Z) -> Zip<Self, Z::Iter>
where
Z: IntoParallelIterator,
Z::Iter: IndexedParallelIterator,
{
Zip::new(self, zip_op.into_par_iter())
}
/// The same as `Zip`, but requires that both iterators have the same length.
///
/// # Panics
/// Will panic if `self` and `zip_op` are not the same length.
///
/// ```should_panic
/// use rayon::prelude::*;
///
/// let one = [1u8];
/// let two = [2u8, 2];
/// let one_iter = one.par_iter();
/// let two_iter = two.par_iter();
///
/// // this will panic
/// let zipped: Vec<(&u8, &u8)> = one_iter.zip_eq(two_iter).collect();
///
/// // we should never get here
/// assert_eq!(1, zipped.len());
/// ```
#[track_caller]
fn zip_eq<Z>(self, zip_op: Z) -> ZipEq<Self, Z::Iter>
where
Z: IntoParallelIterator,
Z::Iter: IndexedParallelIterator,
{
let zip_op_iter = zip_op.into_par_iter();
assert_eq!(
self.len(),
zip_op_iter.len(),
"iterators must have the same length"
);
ZipEq::new(self, zip_op_iter)
}
/// Interleaves elements of this iterator and the other given
/// iterator. Alternately yields elements from this iterator and
/// the given iterator, until both are exhausted. If one iterator
/// is exhausted before the other, the last elements are provided
/// from the other.
///
/// # Examples
///
/// ```
/// use rayon::prelude::*;
/// let (x, y) = (vec![1, 2], vec![3, 4, 5, 6]);
/// let r: Vec<i32> = x.into_par_iter().interleave(y).collect();
/// assert_eq!(r, vec![1, 3, 2, 4, 5, 6]);
/// ```
fn interleave<I>(self, other: I) -> Interleave<Self, I::Iter>
where
I: IntoParallelIterator<Item = Self::Item>,
I::Iter: IndexedParallelIterator<Item = Self::Item>,
{
Interleave::new(self, other.into_par_iter())
}
/// Interleaves elements of this iterator and the other given
/// iterator, until one is exhausted.
///
/// # Examples
///
/// ```
/// use rayon::prelude::*;
/// let (x, y) = (vec![1, 2, 3, 4], vec![5, 6]);
/// let r: Vec<i32> = x.into_par_iter().interleave_shortest(y).collect();
/// assert_eq!(r, vec![1, 5, 2, 6, 3]);
/// ```
fn interleave_shortest<I>(self, other: I) -> InterleaveShortest<Self, I::Iter>
where
I: IntoParallelIterator<Item = Self::Item>,
I::Iter: IndexedParallelIterator<Item = Self::Item>,
{
InterleaveShortest::new(self, other.into_par_iter())
}
/// Splits an iterator up into fixed-size chunks.
///
/// Returns an iterator that returns `Vec`s of the given number of elements.
/// If the number of elements in the iterator is not divisible by `chunk_size`,
/// the last chunk may be shorter than `chunk_size`.
///
/// See also [`par_chunks()`] and [`par_chunks_mut()`] for similar behavior on
/// slices, without having to allocate intermediate `Vec`s for the chunks.
///
/// [`par_chunks()`]: ../slice/trait.ParallelSlice.html#method.par_chunks
/// [`par_chunks_mut()`]: ../slice/trait.ParallelSliceMut.html#method.par_chunks_mut
///
/// # Examples
///
/// ```
/// use rayon::prelude::*;
/// let a = vec![1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
/// let r: Vec<Vec<i32>> = a.into_par_iter().chunks(3).collect();
/// assert_eq!(r, vec![vec![1,2,3], vec![4,5,6], vec![7,8,9], vec![10]]);
/// ```
fn chunks(self, chunk_size: usize) -> Chunks<Self> {
assert!(chunk_size != 0, "chunk_size must not be zero");
Chunks::new(self, chunk_size)
}
/// Splits an iterator into fixed-size chunks, performing a sequential [`fold()`] on
/// each chunk.
///
/// Returns an iterator that produces a folded result for each chunk of items
/// produced by this iterator.
///
/// This works essentially like:
///
/// ```text
/// iter.chunks(chunk_size)
/// .map(|chunk|
/// chunk.into_iter()
/// .fold(identity, fold_op)
/// )
/// ```
///
/// except there is no per-chunk allocation overhead.
///
/// [`fold()`]: std::iter::Iterator#method.fold
///
/// **Panics** if `chunk_size` is 0.
///
/// # Examples
///
/// ```
/// use rayon::prelude::*;
/// let nums = vec![1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
/// let chunk_sums = nums.into_par_iter().fold_chunks(2, || 0, |a, n| a + n).collect::<Vec<_>>();
/// assert_eq!(chunk_sums, vec![3, 7, 11, 15, 19]);
/// ```
#[track_caller]
fn fold_chunks<T, ID, F>(
self,
chunk_size: usize,
identity: ID,
fold_op: F,
) -> FoldChunks<Self, ID, F>
where
ID: Fn() -> T + Send + Sync,
F: Fn(T, Self::Item) -> T + Send + Sync,
T: Send,
{
assert!(chunk_size != 0, "chunk_size must not be zero");
FoldChunks::new(self, chunk_size, identity, fold_op)
}
/// Splits an iterator into fixed-size chunks, performing a sequential [`fold()`] on
/// each chunk.
///
/// Returns an iterator that produces a folded result for each chunk of items
/// produced by this iterator.
///
/// This works essentially like `fold_chunks(chunk_size, || init.clone(), fold_op)`,
/// except it doesn't require the `init` type to be `Sync`, nor any other form of
/// added synchronization.
///
/// [`fold()`]: std::iter::Iterator#method.fold
///
/// **Panics** if `chunk_size` is 0.
///
/// # Examples
///
/// ```
/// use rayon::prelude::*;
/// let nums = vec![1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
/// let chunk_sums = nums.into_par_iter().fold_chunks_with(2, 0, |a, n| a + n).collect::<Vec<_>>();
/// assert_eq!(chunk_sums, vec![3, 7, 11, 15, 19]);
/// ```
#[track_caller]
fn fold_chunks_with<T, F>(
self,
chunk_size: usize,
init: T,
fold_op: F,
) -> FoldChunksWith<Self, T, F>
where
T: Send + Clone,
F: Fn(T, Self::Item) -> T + Send + Sync,
{
assert!(chunk_size != 0, "chunk_size must not be zero");
FoldChunksWith::new(self, chunk_size, init, fold_op)
}
/// Lexicographically compares the elements of this `ParallelIterator` with those of
/// another.
///
/// # Examples
///
/// ```
/// use rayon::prelude::*;
/// use std::cmp::Ordering::*;
///
/// let x = vec![1, 2, 3];
/// assert_eq!(x.par_iter().cmp(&vec![1, 3, 0]), Less);
/// assert_eq!(x.par_iter().cmp(&vec![1, 2, 3]), Equal);
/// assert_eq!(x.par_iter().cmp(&vec![1, 2]), Greater);
/// ```
fn cmp<I>(self, other: I) -> Ordering
where
I: IntoParallelIterator<Item = Self::Item>,
I::Iter: IndexedParallelIterator,
Self::Item: Ord,
{
#[inline]
fn ordering<T: Ord>((x, y): (T, T)) -> Ordering {
Ord::cmp(&x, &y)
}
#[inline]
fn inequal(&ord: &Ordering) -> bool {
ord != Ordering::Equal
}
let other = other.into_par_iter();
let ord_len = self.len().cmp(&other.len());
self.zip(other)
.map(ordering)
.find_first(inequal)
.unwrap_or(ord_len)
}
/// Lexicographically compares the elements of this `ParallelIterator` with those of
/// another.
///
/// # Examples
///
/// ```
/// use rayon::prelude::*;
/// use std::cmp::Ordering::*;
/// use std::f64::NAN;
///
/// let x = vec![1.0, 2.0, 3.0];
/// assert_eq!(x.par_iter().partial_cmp(&vec![1.0, 3.0, 0.0]), Some(Less));
/// assert_eq!(x.par_iter().partial_cmp(&vec![1.0, 2.0, 3.0]), Some(Equal));
/// assert_eq!(x.par_iter().partial_cmp(&vec![1.0, 2.0]), Some(Greater));
/// assert_eq!(x.par_iter().partial_cmp(&vec![1.0, NAN]), None);
/// ```
fn partial_cmp<I>(self, other: I) -> Option<Ordering>
where
I: IntoParallelIterator,
I::Iter: IndexedParallelIterator,
Self::Item: PartialOrd<I::Item>,
{
#[inline]
fn ordering<T: PartialOrd<U>, U>((x, y): (T, U)) -> Option<Ordering> {
PartialOrd::partial_cmp(&x, &y)
}
#[inline]
fn inequal(&ord: &Option<Ordering>) -> bool {
ord != Some(Ordering::Equal)
}
let other = other.into_par_iter();
let ord_len = self.len().cmp(&other.len());
self.zip(other)
.map(ordering)
.find_first(inequal)
.unwrap_or(Some(ord_len))
}
/// Determines if the elements of this `ParallelIterator`
/// are equal to those of another
fn eq<I>(self, other: I) -> bool
where
I: IntoParallelIterator,
I::Iter: IndexedParallelIterator,
Self::Item: PartialEq<I::Item>,
{
#[inline]
fn eq<T: PartialEq<U>, U>((x, y): (T, U)) -> bool {
PartialEq::eq(&x, &y)
}
let other = other.into_par_iter();
self.len() == other.len() && self.zip(other).all(eq)
}
/// Determines if the elements of this `ParallelIterator`
/// are unequal to those of another
fn ne<I>(self, other: I) -> bool
where
I: IntoParallelIterator,
I::Iter: IndexedParallelIterator,
Self::Item: PartialEq<I::Item>,
{
!self.eq(other)
}
/// Determines if the elements of this `ParallelIterator`
/// are lexicographically less than those of another.
fn lt<I>(self, other: I) -> bool
where
I: IntoParallelIterator,
I::Iter: IndexedParallelIterator,
Self::Item: PartialOrd<I::Item>,
{
self.partial_cmp(other) == Some(Ordering::Less)
}
/// Determines if the elements of this `ParallelIterator`
/// are less or equal to those of another.
fn le<I>(self, other: I) -> bool
where
I: IntoParallelIterator,
I::Iter: IndexedParallelIterator,
Self::Item: PartialOrd<I::Item>,
{
let ord = self.partial_cmp(other);
ord == Some(Ordering::Equal) || ord == Some(Ordering::Less)
}
/// Determines if the elements of this `ParallelIterator`
/// are lexicographically greater than those of another.
fn gt<I>(self, other: I) -> bool
where
I: IntoParallelIterator,
I::Iter: IndexedParallelIterator,
Self::Item: PartialOrd<I::Item>,
{
self.partial_cmp(other) == Some(Ordering::Greater)
}
/// Determines if the elements of this `ParallelIterator`
/// are less or equal to those of another.
fn ge<I>(self, other: I) -> bool
where
I: IntoParallelIterator,
I::Iter: IndexedParallelIterator,
Self::Item: PartialOrd<I::Item>,
{
let ord = self.partial_cmp(other);
ord == Some(Ordering::Equal) || ord == Some(Ordering::Greater)
}
/// Yields an index along with each item.
///
/// # Examples
///
/// ```
/// use rayon::prelude::*;
///
/// let chars = vec!['a', 'b', 'c'];
/// let result: Vec<_> = chars
/// .into_par_iter()
/// .enumerate()
/// .collect();
///
/// assert_eq!(result, [(0, 'a'), (1, 'b'), (2, 'c')]);
/// ```
fn enumerate(self) -> Enumerate<Self> {
Enumerate::new(self)
}
/// Creates an iterator that steps by the given amount
///
/// # Examples
///
/// ```
///use rayon::prelude::*;
///
/// let range = (3..10);
/// let result: Vec<i32> = range
/// .into_par_iter()
/// .step_by(3)
/// .collect();
///
/// assert_eq!(result, [3, 6, 9])
/// ```
fn step_by(self, step: usize) -> StepBy<Self> {
StepBy::new(self, step)
}
/// Creates an iterator that skips the first `n` elements.
///
/// # Examples
///
/// ```
/// use rayon::prelude::*;
///
/// let result: Vec<_> = (0..100)
/// .into_par_iter()
/// .skip(95)
/// .collect();
///
/// assert_eq!(result, [95, 96, 97, 98, 99]);
/// ```
fn skip(self, n: usize) -> Skip<Self> {
Skip::new(self, n)
}
/// Creates an iterator that yields the first `n` elements.
///
/// # Examples
///
/// ```
/// use rayon::prelude::*;
///
/// let result: Vec<_> = (0..100)
/// .into_par_iter()
/// .take(5)
/// .collect();
///
/// assert_eq!(result, [0, 1, 2, 3, 4]);
/// ```
fn take(self, n: usize) -> Take<Self> {
Take::new(self, n)
}
/// Searches for **some** item in the parallel iterator that
/// matches the given predicate, and returns its index. Like
/// `ParallelIterator::find_any`, the parallel search will not
/// necessarily find the **first** match, and once a match is
/// found we'll attempt to stop processing any more.
///
/// # Examples
///
/// ```
/// use rayon::prelude::*;
///
/// let a = [1, 2, 3, 3];
///
/// let i = a.par_iter().position_any(|&x| x == 3).expect("found");
/// assert!(i == 2 || i == 3);
///
/// assert_eq!(a.par_iter().position_any(|&x| x == 100), None);
/// ```
fn position_any<P>(self, predicate: P) -> Option<usize>
where
P: Fn(Self::Item) -> bool + Sync + Send,
{
#[inline]
fn check(&(_, p): &(usize, bool)) -> bool {
p
}
let (i, _) = self.map(predicate).enumerate().find_any(check)?;
Some(i)
}
/// Searches for the sequentially **first** item in the parallel iterator
/// that matches the given predicate, and returns its index.
///
/// Like `ParallelIterator::find_first`, 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,
/// `position_any` is a better choice.
///
/// # Examples
///
/// ```
/// use rayon::prelude::*;
///
/// let a = [1, 2, 3, 3];
///
/// assert_eq!(a.par_iter().position_first(|&x| x == 3), Some(2));
///
/// assert_eq!(a.par_iter().position_first(|&x| x == 100), None);
/// ```
fn position_first<P>(self, predicate: P) -> Option<usize>
where
P: Fn(Self::Item) -> bool + Sync + Send,
{
#[inline]
fn check(&(_, p): &(usize, bool)) -> bool {
p
}
let (i, _) = self.map(predicate).enumerate().find_first(check)?;
Some(i)
}
/// Searches for the sequentially **last** item in the parallel iterator
/// that matches the given predicate, and returns its index.
///
/// Like `ParallelIterator::find_last`, 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, `position_any` is a better
/// choice.
///
/// # Examples
///
/// ```
/// use rayon::prelude::*;
///
/// let a = [1, 2, 3, 3];
///
/// assert_eq!(a.par_iter().position_last(|&x| x == 3), Some(3));
///
/// assert_eq!(a.par_iter().position_last(|&x| x == 100), None);
/// ```
fn position_last<P>(self, predicate: P) -> Option<usize>
where
P: Fn(Self::Item) -> bool + Sync + Send,
{
#[inline]
fn check(&(_, p): &(usize, bool)) -> bool {
p
}
let (i, _) = self.map(predicate).enumerate().find_last(check)?;
Some(i)
}
#[doc(hidden)]
#[deprecated(
note = "parallel `position` does not search in order -- use `position_any`, \\
`position_first`, or `position_last`"
)]
fn position<P>(self, predicate: P) -> Option<usize>
where
P: Fn(Self::Item) -> bool + Sync + Send,
{
self.position_any(predicate)
}
/// Searches for items in the parallel iterator that match the given
/// predicate, and returns their indices.
///
/// # Examples
///
/// ```
/// use rayon::prelude::*;
///
/// let primes = vec![2, 3, 5, 7, 11, 13, 17, 19, 23, 29];
///
/// // Find the positions of primes congruent to 1 modulo 6
/// let p1mod6: Vec<_> = primes.par_iter().positions(|&p| p % 6 == 1).collect();
/// assert_eq!(p1mod6, [3, 5, 7]); // primes 7, 13, and 19
///
/// // Find the positions of primes congruent to 5 modulo 6
/// let p5mod6: Vec<_> = primes.par_iter().positions(|&p| p % 6 == 5).collect();
/// assert_eq!(p5mod6, [2, 4, 6, 8, 9]); // primes 5, 11, 17, 23, and 29
/// ```
fn positions<P>(self, predicate: P) -> Positions<Self, P>
where
P: Fn(Self::Item) -> bool + Sync + Send,
{
Positions::new(self, predicate)
}
/// Produces a new iterator with the elements of this iterator in
/// reverse order.
///
/// # Examples
///
/// ```
/// use rayon::prelude::*;
///
/// let result: Vec<_> = (0..5)
/// .into_par_iter()
/// .rev()
/// .collect();
///
/// assert_eq!(result, [4, 3, 2, 1, 0]);
/// ```
fn rev(self) -> Rev<Self> {
Rev::new(self)
}
/// Sets the minimum length of iterators desired to process in each
/// rayon job. Rayon will not split any smaller than this length, but
/// of course an iterator could already be smaller to begin with.
///
/// Producers like `zip` and `interleave` will use greater of the two
/// minimums.
/// Chained iterators and iterators inside `flat_map` may each use
/// their own minimum length.
///
/// # Examples
///
/// ```
/// use rayon::prelude::*;
///
/// let min = (0..1_000_000)
/// .into_par_iter()
/// .with_min_len(1234)
/// .fold(|| 0, |acc, _| acc + 1) // count how many are in this segment
/// .min().unwrap();
///
/// assert!(min >= 1234);
/// ```
fn with_min_len(self, min: usize) -> MinLen<Self> {
MinLen::new(self, min)
}
/// Sets the maximum length of iterators desired to process in each
/// rayon job. Rayon will try to split at least below this length,
/// unless that would put it below the length from `with_min_len()`.
/// For example, given min=10 and max=15, a length of 16 will not be
/// split any further.
///
/// Producers like `zip` and `interleave` will use lesser of the two
/// maximums.
/// Chained iterators and iterators inside `flat_map` may each use
/// their own maximum length.
///
/// # Examples
///
/// ```
/// use rayon::prelude::*;
///
/// let max = (0..1_000_000)
/// .into_par_iter()
/// .with_max_len(1234)
/// .fold(|| 0, |acc, _| acc + 1) // count how many are in this segment
/// .max().unwrap();
///
/// assert!(max <= 1234);
/// ```
fn with_max_len(self, max: usize) -> MaxLen<Self> {
MaxLen::new(self, max)
}
/// Produces an exact count of how many items this iterator will
/// produce, presuming no panic occurs.
///
/// # Examples
///
/// ```
/// use rayon::prelude::*;
///
/// let par_iter = (0..100).into_par_iter().zip(vec![0; 10]);
/// assert_eq!(par_iter.len(), 10);
///
/// let vec: Vec<_> = par_iter.collect();
/// assert_eq!(vec.len(), 10);
/// ```
fn len(&self) -> usize;
/// 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. If a split does happen, it
/// will inform the consumer of the index where the split should
/// occur (unlike `ParallelIterator::drive_unindexed()`).
///
/// See the [README] for more details on the internals of parallel
/// iterators.
///
/// [README]: https://github.com/rayon-rs/rayon/blob/master/src/iter/plumbing/README.md
fn drive<C: Consumer<Self::Item>>(self, consumer: C) -> C::Result;
/// Internal method used to define the behavior of this parallel
/// iterator. You should not need to call this directly.
///
/// This method converts the iterator into a producer P and then
/// invokes `callback.callback()` with P. Note that the type of
/// this producer is not defined as part of the API, since
/// `callback` must be defined generically for all producers. This
/// allows the producer type to contain references; it also means
/// that parallel iterators can adjust that type without causing a
/// breaking change.
///
/// See the [README] for more details on the internals of parallel
/// iterators.
///
/// [README]: https://github.com/rayon-rs/rayon/blob/master/src/iter/plumbing/README.md
fn with_producer<CB: ProducerCallback<Self::Item>>(self, callback: CB) -> CB::Output;
}
/// `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.
///
/// `FromParallelIterator` is used through [`ParallelIterator`]'s [`collect()`] method.
///
/// [`ParallelIterator`]: trait.ParallelIterator.html
/// [`collect()`]: trait.ParallelIterator.html#method.collect
///
/// # Examples
///
/// Implementing `FromParallelIterator` for your type:
///
/// ```
/// use rayon::prelude::*;
/// use std::mem;
///
/// struct BlackHole {
/// mass: usize,
/// }
///
/// impl<T: Send> FromParallelIterator<T> for BlackHole {
/// fn from_par_iter<I>(par_iter: I) -> Self
/// where I: IntoParallelIterator<Item = T>
/// {
/// let par_iter = par_iter.into_par_iter();
/// BlackHole {
/// mass: par_iter.count() * mem::size_of::<T>(),
/// }
/// }
/// }
///
/// let bh: BlackHole = (0i32..1000).into_par_iter().collect();
/// assert_eq!(bh.mass, 4000);
/// ```
pub trait FromParallelIterator<T>
where
T: Send,
{
/// Creates an instance of the collection from the parallel iterator `par_iter`.
///
/// If your collection is not naturally parallel, the easiest (and
/// fastest) way to do this is often to collect `par_iter` into a
/// [`LinkedList`] or other intermediate data structure and then
/// sequentially extend your collection. However, a more 'native'
/// technique is to use the [`par_iter.fold`] or
/// [`par_iter.fold_with`] methods to create the collection.
/// Alternatively, if your collection is 'natively' parallel, you
/// can use `par_iter.for_each` to process each element in turn.
///
/// [`LinkedList`]: https://doc.rust-lang.org/std/collections/struct.LinkedList.html
/// [`par_iter.fold`]: trait.ParallelIterator.html#method.fold
/// [`par_iter.fold_with`]: trait.ParallelIterator.html#method.fold_with
/// [`par_iter.for_each`]: trait.ParallelIterator.html#method.for_each
fn from_par_iter<I>(par_iter: I) -> Self
where
I: IntoParallelIterator<Item = T>;
}
/// `ParallelExtend` extends an existing collection with items from a [`ParallelIterator`].
///
/// [`ParallelIterator`]: trait.ParallelIterator.html
///
/// # Examples
///
/// Implementing `ParallelExtend` for your type:
///
/// ```
/// use rayon::prelude::*;
/// use std::mem;
///
/// struct BlackHole {
/// mass: usize,
/// }
///
/// impl<T: Send> ParallelExtend<T> for BlackHole {
/// fn par_extend<I>(&mut self, par_iter: I)
/// where I: IntoParallelIterator<Item = T>
/// {
/// let par_iter = par_iter.into_par_iter();
/// self.mass += par_iter.count() * mem::size_of::<T>();
/// }
/// }
///
/// let mut bh = BlackHole { mass: 0 };
/// bh.par_extend(0i32..1000);
/// assert_eq!(bh.mass, 4000);
/// bh.par_extend(0i64..10);
/// assert_eq!(bh.mass, 4080);
/// ```
pub trait ParallelExtend<T>
where
T: Send,
{
/// Extends an instance of the collection with the elements drawn
/// from the parallel iterator `par_iter`.
///
/// # Examples
///
/// ```
/// use rayon::prelude::*;
///
/// let mut vec = vec![];
/// vec.par_extend(0..5);
/// vec.par_extend((0..5).into_par_iter().map(|i| i * i));
/// assert_eq!(vec, [0, 1, 2, 3, 4, 0, 1, 4, 9, 16]);
/// ```
fn par_extend<I>(&mut self, par_iter: I)
where
I: IntoParallelIterator<Item = T>;
}
/// `ParallelDrainFull` creates a parallel iterator that moves all items
/// from a collection while retaining the original capacity.
///
/// Types which are indexable typically implement [`ParallelDrainRange`]
/// instead, where you can drain fully with `par_drain(..)`.
///
/// [`ParallelDrainRange`]: trait.ParallelDrainRange.html
pub trait ParallelDrainFull {
/// The draining parallel iterator type that will be created.
type Iter: ParallelIterator<Item = Self::Item>;
/// The type of item that the parallel iterator will produce.
/// This is usually the same as `IntoParallelIterator::Item`.
type Item: Send;
/// Returns a draining parallel iterator over an entire collection.
///
/// When the iterator is dropped, all items are removed, even if the
/// iterator was not fully consumed. If the iterator is leaked, for example
/// using `std::mem::forget`, it is unspecified how many items are removed.
///
/// # Examples
///
/// ```
/// use rayon::prelude::*;
/// use std::collections::{BinaryHeap, HashSet};
///
/// let squares: HashSet<i32> = (0..10).map(|x| x * x).collect();
///
/// let mut heap: BinaryHeap<_> = squares.iter().copied().collect();
/// assert_eq!(
/// // heaps are drained in arbitrary order
/// heap.par_drain()
/// .inspect(|x| assert!(squares.contains(x)))
/// .count(),
/// squares.len(),
/// );
/// assert!(heap.is_empty());
/// assert!(heap.capacity() >= squares.len());
/// ```
fn par_drain(self) -> Self::Iter;
}
/// `ParallelDrainRange` creates a parallel iterator that moves a range of items
/// from a collection while retaining the original capacity.
///
/// Types which are not indexable may implement [`ParallelDrainFull`] instead.
///
/// [`ParallelDrainFull`]: trait.ParallelDrainFull.html
pub trait ParallelDrainRange<Idx = usize> {
/// The draining parallel iterator type that will be created.
type Iter: ParallelIterator<Item = Self::Item>;
/// The type of item that the parallel iterator will produce.
/// This is usually the same as `IntoParallelIterator::Item`.
type Item: Send;
/// Returns a draining parallel iterator over a range of the collection.
///
/// When the iterator is dropped, all items in the range are removed, even
/// if the iterator was not fully consumed. If the iterator is leaked, for
/// example using `std::mem::forget`, it is unspecified how many items are
/// removed.
///
/// # Examples
///
/// ```
/// use rayon::prelude::*;
///
/// let squares: Vec<i32> = (0..10).map(|x| x * x).collect();
///
/// println!("RangeFull");
/// let mut vec = squares.clone();
/// assert!(vec.par_drain(..)
/// .eq(squares.par_iter().copied()));
/// assert!(vec.is_empty());
/// assert!(vec.capacity() >= squares.len());
///
/// println!("RangeFrom");
/// let mut vec = squares.clone();
/// assert!(vec.par_drain(5..)
/// .eq(squares[5..].par_iter().copied()));
/// assert_eq!(&vec[..], &squares[..5]);
/// assert!(vec.capacity() >= squares.len());
///
/// println!("RangeTo");
/// let mut vec = squares.clone();
/// assert!(vec.par_drain(..5)
/// .eq(squares[..5].par_iter().copied()));
/// assert_eq!(&vec[..], &squares[5..]);
/// assert!(vec.capacity() >= squares.len());
///
/// println!("RangeToInclusive");
/// let mut vec = squares.clone();
/// assert!(vec.par_drain(..=5)
/// .eq(squares[..=5].par_iter().copied()));
/// assert_eq!(&vec[..], &squares[6..]);
/// assert!(vec.capacity() >= squares.len());
///
/// println!("Range");
/// let mut vec = squares.clone();
/// assert!(vec.par_drain(3..7)
/// .eq(squares[3..7].par_iter().copied()));
/// assert_eq!(&vec[..3], &squares[..3]);
/// assert_eq!(&vec[3..], &squares[7..]);
/// assert!(vec.capacity() >= squares.len());
///
/// println!("RangeInclusive");
/// let mut vec = squares.clone();
/// assert!(vec.par_drain(3..=7)
/// .eq(squares[3..=7].par_iter().copied()));
/// assert_eq!(&vec[..3], &squares[..3]);
/// assert_eq!(&vec[3..], &squares[8..]);
/// assert!(vec.capacity() >= squares.len());
/// ```
fn par_drain<R: RangeBounds<Idx>>(self, range: R) -> Self::Iter;
}
/// We hide the `Try` trait in a private module, as it's only meant to be a
/// stable clone of the standard library's `Try` trait, as yet unstable.
mod private {
use std::convert::Infallible;
use std::ops::ControlFlow::{self, Break, Continue};
use std::task::Poll;
/// Clone of `std::ops::Try`.
///
/// Implementing this trait is not permitted outside of `rayon`.
pub trait Try {
private_decl! {}
type Output;
type Residual;
fn from_output(output: Self::Output) -> Self;
fn from_residual(residual: Self::Residual) -> Self;
fn branch(self) -> ControlFlow<Self::Residual, Self::Output>;
}
impl<B, C> Try for ControlFlow<B, C> {
private_impl! {}
type Output = C;
type Residual = ControlFlow<B, Infallible>;
fn from_output(output: Self::Output) -> Self {
Continue(output)
}
fn from_residual(residual: Self::Residual) -> Self {
match residual {
Break(b) => Break(b),
Continue(_) => unreachable!(),
}
}
fn branch(self) -> ControlFlow<Self::Residual, Self::Output> {
match self {
Continue(c) => Continue(c),
Break(b) => Break(Break(b)),
}
}
}
impl<T> Try for Option<T> {
private_impl! {}
type Output = T;
type Residual = Option<Infallible>;
fn from_output(output: Self::Output) -> Self {
Some(output)
}
fn from_residual(residual: Self::Residual) -> Self {
match residual {
None => None,
Some(_) => unreachable!(),
}
}
fn branch(self) -> ControlFlow<Self::Residual, Self::Output> {
match self {
Some(c) => Continue(c),
None => Break(None),
}
}
}
impl<T, E> Try for Result<T, E> {
private_impl! {}
type Output = T;
type Residual = Result<Infallible, E>;
fn from_output(output: Self::Output) -> Self {
Ok(output)
}
fn from_residual(residual: Self::Residual) -> Self {
match residual {
Err(e) => Err(e),
Ok(_) => unreachable!(),
}
}
fn branch(self) -> ControlFlow<Self::Residual, Self::Output> {
match self {
Ok(c) => Continue(c),
Err(e) => Break(Err(e)),
}
}
}
impl<T, E> Try for Poll<Result<T, E>> {
private_impl! {}
type Output = Poll<T>;
type Residual = Result<Infallible, E>;
fn from_output(output: Self::Output) -> Self {
output.map(Ok)
}
fn from_residual(residual: Self::Residual) -> Self {
match residual {
Err(e) => Poll::Ready(Err(e)),
Ok(_) => unreachable!(),
}
}
fn branch(self) -> ControlFlow<Self::Residual, Self::Output> {
match self {
Poll::Pending => Continue(Poll::Pending),
Poll::Ready(Ok(c)) => Continue(Poll::Ready(c)),
Poll::Ready(Err(e)) => Break(Err(e)),
}
}
}
impl<T, E> Try for Poll<Option<Result<T, E>>> {
private_impl! {}
type Output = Poll<Option<T>>;
type Residual = Result<Infallible, E>;
fn from_output(output: Self::Output) -> Self {
match output {
Poll::Ready(o) => Poll::Ready(o.map(Ok)),
Poll::Pending => Poll::Pending,
}
}
fn from_residual(residual: Self::Residual) -> Self {
match residual {
Err(e) => Poll::Ready(Some(Err(e))),
Ok(_) => unreachable!(),
}
}
fn branch(self) -> ControlFlow<Self::Residual, Self::Output> {
match self {
Poll::Pending => Continue(Poll::Pending),
Poll::Ready(None) => Continue(Poll::Ready(None)),
Poll::Ready(Some(Ok(c))) => Continue(Poll::Ready(Some(c))),
Poll::Ready(Some(Err(e))) => Break(Err(e)),
}
}
}
}