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#![cfg(feature = "use_alloc")]
use Option::{self as State, None as ProductEnded, Some as ProductInProgress};
use Option::{self as CurrentItems, None as NotYetPopulated, Some as Populated};
use alloc::vec::Vec;
use crate::size_hint;
#[derive(Clone)]
/// An iterator adaptor that iterates over the cartesian product of
/// multiple iterators of type `I`.
///
/// An iterator element type is `Vec<I::Item>`.
///
/// See [`.multi_cartesian_product()`](crate::Itertools::multi_cartesian_product)
/// for more information.
#[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
pub struct MultiProduct<I>(State<MultiProductInner<I>>)
where
I: Iterator + Clone,
I::Item: Clone;
#[derive(Clone)]
/// Internals for `MultiProduct`.
struct MultiProductInner<I>
where
I: Iterator + Clone,
I::Item: Clone,
{
/// Holds the iterators.
iters: Vec<MultiProductIter<I>>,
/// Not populated at the beginning then it holds the current item of each iterator.
cur: CurrentItems<Vec<I::Item>>,
}
impl<I> std::fmt::Debug for MultiProduct<I>
where
I: Iterator + Clone + std::fmt::Debug,
I::Item: Clone + std::fmt::Debug,
{
debug_fmt_fields!(MultiProduct, 0);
}
impl<I> std::fmt::Debug for MultiProductInner<I>
where
I: Iterator + Clone + std::fmt::Debug,
I::Item: Clone + std::fmt::Debug,
{
debug_fmt_fields!(MultiProductInner, iters, cur);
}
/// Create a new cartesian product iterator over an arbitrary number
/// of iterators of the same type.
///
/// Iterator element is of type `Vec<H::Item::Item>`.
pub fn multi_cartesian_product<H>(iters: H) -> MultiProduct<<H::Item as IntoIterator>::IntoIter>
where
H: Iterator,
H::Item: IntoIterator,
<H::Item as IntoIterator>::IntoIter: Clone,
<H::Item as IntoIterator>::Item: Clone,
{
let inner = MultiProductInner {
iters: iters
.map(|i| MultiProductIter::new(i.into_iter()))
.collect(),
cur: NotYetPopulated,
};
MultiProduct(ProductInProgress(inner))
}
#[derive(Clone, Debug)]
/// Holds the state of a single iterator within a `MultiProduct`.
struct MultiProductIter<I>
where
I: Iterator + Clone,
I::Item: Clone,
{
iter: I,
iter_orig: I,
}
impl<I> MultiProductIter<I>
where
I: Iterator + Clone,
I::Item: Clone,
{
fn new(iter: I) -> Self {
Self {
iter: iter.clone(),
iter_orig: iter,
}
}
}
impl<I> Iterator for MultiProduct<I>
where
I: Iterator + Clone,
I::Item: Clone,
{
type Item = Vec<I::Item>;
fn next(&mut self) -> Option<Self::Item> {
// This fuses the iterator.
let inner = self.0.as_mut()?;
match &mut inner.cur {
Populated(values) => {
debug_assert!(!inner.iters.is_empty());
// Find (from the right) a non-finished iterator and
// reset the finished ones encountered.
for (iter, item) in inner.iters.iter_mut().zip(values.iter_mut()).rev() {
if let Some(new) = iter.iter.next() {
*item = new;
return Some(values.clone());
} else {
iter.iter = iter.iter_orig.clone();
// `cur` is populated so the untouched `iter_orig` can not be empty.
*item = iter.iter.next().unwrap();
}
}
self.0 = ProductEnded;
None
}
// Only the first time.
NotYetPopulated => {
let next: Option<Vec<_>> = inner.iters.iter_mut().map(|i| i.iter.next()).collect();
if next.is_none() || inner.iters.is_empty() {
// This cartesian product had at most one item to generate and now ends.
self.0 = ProductEnded;
} else {
inner.cur.clone_from(&next);
}
next
}
}
}
fn count(self) -> usize {
match self.0 {
ProductEnded => 0,
// The iterator is fresh so the count is the product of the length of each iterator:
// - If one of them is empty, stop counting.
// - Less `count()` calls than the general case.
ProductInProgress(MultiProductInner {
iters,
cur: NotYetPopulated,
}) => iters
.into_iter()
.map(|iter| iter.iter_orig.count())
.try_fold(1, |product, count| {
if count == 0 {
None
} else {
Some(product * count)
}
})
.unwrap_or_default(),
// The general case.
ProductInProgress(MultiProductInner {
iters,
cur: Populated(_),
}) => iters.into_iter().fold(0, |mut acc, iter| {
if acc != 0 {
acc *= iter.iter_orig.count();
}
acc + iter.iter.count()
}),
}
}
fn size_hint(&self) -> (usize, Option<usize>) {
match &self.0 {
ProductEnded => (0, Some(0)),
ProductInProgress(MultiProductInner {
iters,
cur: NotYetPopulated,
}) => iters
.iter()
.map(|iter| iter.iter_orig.size_hint())
.fold((1, Some(1)), size_hint::mul),
ProductInProgress(MultiProductInner {
iters,
cur: Populated(_),
}) => {
if let [first, tail @ ..] = &iters[..] {
tail.iter().fold(first.iter.size_hint(), |mut sh, iter| {
sh = size_hint::mul(sh, iter.iter_orig.size_hint());
size_hint::add(sh, iter.iter.size_hint())
})
} else {
// Since it is populated, this cartesian product has started so `iters` is not empty.
unreachable!()
}
}
}
}
fn last(self) -> Option<Self::Item> {
let MultiProductInner { iters, cur } = self.0?;
// Collect the last item of each iterator of the product.
if let Populated(values) = cur {
let mut count = iters.len();
let last = iters
.into_iter()
.zip(values)
.map(|(i, value)| {
i.iter.last().unwrap_or_else(|| {
// The iterator is empty, use its current `value`.
count -= 1;
value
})
})
.collect();
if count == 0 {
// `values` was the last item.
None
} else {
Some(last)
}
} else {
iters.into_iter().map(|i| i.iter.last()).collect()
}
}
}
impl<I> std::iter::FusedIterator for MultiProduct<I>
where
I: Iterator + Clone,
I::Item: Clone,
{
}