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use super::plumbing::*;
use super::*;

/// `Flatten` turns each element to an iterator, then flattens these iterators
/// together. This struct is created by the [`flatten()`] method on
/// [`ParallelIterator`].
///
/// [`flatten()`]: trait.ParallelIterator.html#method.flatten
/// [`ParallelIterator`]: trait.ParallelIterator.html
#[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
#[derive(Debug, Clone)]
pub struct Flatten<I: ParallelIterator> {
    base: I,
}

/// Create a new `Flatten` iterator.
///
/// NB: Not part of the public API.
pub fn new<I, PI>(base: I) -> Flatten<I>
    where I: ParallelIterator<Item = PI>,
          PI: IntoParallelIterator + Send
{
    Flatten {
        base: base,
    }
}

impl<I, PI> ParallelIterator for Flatten<I>
    where I: ParallelIterator<Item = PI>,
          PI: IntoParallelIterator + Send
{
    type Item = PI::Item;

    fn drive_unindexed<C>(self, consumer: C) -> C::Result
        where C: UnindexedConsumer<Self::Item>
    {
        self.base.flat_map(|x| x).drive_unindexed(consumer)
    }
}