use super::size_hint;
use std::iter::{Fuse, FusedIterator};
pub trait IntersperseElement<Item> {
fn generate(&mut self) -> Item;
}
#[derive(Debug, Clone)]
pub struct IntersperseElementSimple<Item>(Item);
impl<Item: Clone> IntersperseElement<Item> for IntersperseElementSimple<Item> {
fn generate(&mut self) -> Item {
self.0.clone()
}
}
pub type Intersperse<I> = IntersperseWith<I, IntersperseElementSimple<<I as Iterator>::Item>>;
pub fn intersperse<I>(iter: I, elt: I::Item) -> Intersperse<I>
where
I: Iterator,
{
intersperse_with(iter, IntersperseElementSimple(elt))
}
impl<Item, F: FnMut() -> Item> IntersperseElement<Item> for F {
fn generate(&mut self) -> Item {
self()
}
}
#[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
#[derive(Clone, Debug)]
pub struct IntersperseWith<I, ElemF>
where
I: Iterator,
{
element: ElemF,
iter: Fuse<I>,
peek: Option<Option<I::Item>>,
}
pub fn intersperse_with<I, ElemF>(iter: I, elt: ElemF) -> IntersperseWith<I, ElemF>
where
I: Iterator,
{
IntersperseWith {
peek: None,
iter: iter.fuse(),
element: elt,
}
}
impl<I, ElemF> Iterator for IntersperseWith<I, ElemF>
where
I: Iterator,
ElemF: IntersperseElement<I::Item>,
{
type Item = I::Item;
#[inline]
fn next(&mut self) -> Option<Self::Item> {
let Self {
element,
iter,
peek,
} = self;
match peek {
Some(item @ Some(_)) => item.take(),
Some(None) => match iter.next() {
new @ Some(_) => {
*peek = Some(new);
Some(element.generate())
}
None => None,
},
None => {
*peek = Some(None);
iter.next()
}
}
}
fn size_hint(&self) -> (usize, Option<usize>) {
let mut sh = self.iter.size_hint();
sh = size_hint::add(sh, sh);
match self.peek {
Some(Some(_)) => size_hint::add_scalar(sh, 1),
Some(None) => sh,
None => size_hint::sub_scalar(sh, 1),
}
}
fn fold<B, F>(self, init: B, mut f: F) -> B
where
Self: Sized,
F: FnMut(B, Self::Item) -> B,
{
let Self {
mut element,
mut iter,
peek,
} = self;
let mut accum = init;
if let Some(x) = peek.unwrap_or_else(|| iter.next()) {
accum = f(accum, x);
}
iter.fold(accum, |accum, x| {
let accum = f(accum, element.generate());
f(accum, x)
})
}
}
impl<I, ElemF> FusedIterator for IntersperseWith<I, ElemF>
where
I: Iterator,
ElemF: IntersperseElement<I::Item>,
{
}