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use std::iter::{Fuse, FusedIterator};
use super::size_hint;
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()
}
}
/// An iterator adaptor to insert a particular value
/// between each element of the adapted iterator.
///
/// Iterator element type is `I::Item`
///
/// This iterator is *fused*.
///
/// See [`.intersperse()`](crate::Itertools::intersperse) for more information.
pub type Intersperse<I> = IntersperseWith<I, IntersperseElementSimple<<I as Iterator>::Item>>;
/// Create a new Intersperse iterator
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()
}
}
/// An iterator adaptor to insert a particular value created by a function
/// between each element of the adapted iterator.
///
/// Iterator element type is `I::Item`
///
/// This iterator is *fused*.
///
/// See [`.intersperse_with()`](crate::Itertools::intersperse_with) for more information.
#[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<I::Item>,
}
/// Create a new `IntersperseWith` iterator
pub fn intersperse_with<I, ElemF>(iter: I, elt: ElemF) -> IntersperseWith<I, ElemF>
where I: Iterator,
{
let mut iter = iter.fuse();
IntersperseWith {
peek: iter.next(),
iter,
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> {
if self.peek.is_some() {
self.peek.take()
} else {
self.peek = self.iter.next();
if self.peek.is_some() {
Some(self.element.generate())
} else {
None
}
}
}
fn size_hint(&self) -> (usize, Option<usize>) {
// 2 * SH + { 1 or 0 }
let has_peek = self.peek.is_some() as usize;
let sh = self.iter.size_hint();
size_hint::add_scalar(size_hint::add(sh, sh), has_peek)
}
fn fold<B, F>(mut self, init: B, mut f: F) -> B where
Self: Sized, F: FnMut(B, Self::Item) -> B,
{
let mut accum = init;
if let Some(x) = self.peek.take() {
accum = f(accum, x);
}
let element = &mut self.element;
self.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>
{}