Is there a way to directly consume a Rayon chain without collecting it first?

问题

I am using Rayon to produce reasonably large return values. This uses a lot of memory when collecting all returned values into a Vec. Is there a way to avoid creating a Vec and directly consuming as an iterable?

Here is an example which doesn't work:

fn main() {
    let numbers: Vec<_> = "12.03 0.3 44.2 45 zzz".split_whitespace().collect();

    let x = numbers
        .par_iter()
        .map(|n| n.parse::<f32>())
        .filter_map(|n| n.ok());

    for n in x {
        println!("{:?}", n);
    }
}

error[E0277]: the trait bound `rayon::iter::FilterMap<rayon::iter::Map<rayon::slice::Iter<'_, &str>, [closure@src/main.rs:10:14: 10:34]>, [closure@src/main.rs:11:21: 11:31]>: std::iter::Iterator` is not satisfied
   |
13 |     for n in x {
   |              ^ `rayon::iter::FilterMap<rayon::iter::Map<rayon::slice::Iter<'_, &str>, [closure@src/main.rs:10:14: 10:34]>, [closure@src/main.rs:11:21: 11:31]>` is not an iterator; maybe try calling `.iter()` or a similar method
   |
   = help: the trait `std::iter::Iterator` is not implemented for `rayon::iter::FilterMap<rayon::iter::Map<rayon::slice::Iter<'_, &str>, [closure@src/main.rs:10:14: 10:34]>, [closure@src/main.rs:11:21: 11:31]>`
   = note: required by `std::iter::IntoIterator::into_iter`

playground

回答1:

You are looking for ParallelIterator::for_each:

extern crate rayon; // 1.0.2

use rayon::prelude::*;

fn main() {
    let numbers = ["12.03", "0.3", "44.2", "45", "zzz"];

    let x = numbers.par_iter().flat_map(|n| n.parse::<f32>());

    x.for_each(|n| {
        println!("{:?}", n);
    });
}

ParallelIterator::for_each_with
ParallelIterator::try_for_each
ParallelIterator::try_for_each_with