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use super::plumbing::*;
use super::*;
use std::cmp::min;
/// `Take` is an iterator that iterates over the first `n` elements.
/// This struct is created by the [`take()`] method on [`IndexedParallelIterator`]
///
/// [`take()`]: trait.IndexedParallelIterator.html#method.take
/// [`IndexedParallelIterator`]: trait.IndexedParallelIterator.html
#[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
#[derive(Debug, Clone)]
pub struct Take<I> {
base: I,
n: usize,
}
impl<I> Take<I>
where
I: IndexedParallelIterator,
{
/// Creates a new `Take` iterator.
pub(super) fn new(base: I, n: usize) -> Self {
let n = min(base.len(), n);
Take { base, n }
}
}
impl<I> ParallelIterator for Take<I>
where
I: IndexedParallelIterator,
{
type Item = I::Item;
fn drive_unindexed<C>(self, consumer: C) -> C::Result
where
C: UnindexedConsumer<Self::Item>,
{
bridge(self, consumer)
}
fn opt_len(&self) -> Option<usize> {
Some(self.len())
}
}
impl<I> IndexedParallelIterator for Take<I>
where
I: IndexedParallelIterator,
{
fn len(&self) -> usize {
self.n
}
fn drive<C: Consumer<Self::Item>>(self, consumer: C) -> C::Result {
bridge(self, consumer)
}
fn with_producer<CB>(self, callback: CB) -> CB::Output
where
CB: ProducerCallback<Self::Item>,
{
return self.base.with_producer(Callback {
callback,
n: self.n,
});
struct Callback<CB> {
callback: CB,
n: usize,
}
impl<T, CB> ProducerCallback<T> for Callback<CB>
where
CB: ProducerCallback<T>,
{
type Output = CB::Output;
fn callback<P>(self, base: P) -> CB::Output
where
P: Producer<Item = T>,
{
let (producer, _) = base.split_at(self.n);
self.callback.callback(producer)
}
}
}
}