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use crate::fmt;
use crate::iter::{adapters::SourceIter, InPlaceIterable};
use crate::ops::{ControlFlow, Try};
#[must_use = "iterators are lazy and do nothing unless consumed"]
#[stable(feature = "rust1", since = "1.0.0")]
#[derive(Clone)]
pub struct Scan<I, St, F> {
iter: I,
f: F,
state: St,
}
impl<I, St, F> Scan<I, St, F> {
pub(in crate::iter) fn new(iter: I, state: St, f: F) -> Scan<I, St, F> {
Scan { iter, state, f }
}
}
#[stable(feature = "core_impl_debug", since = "1.9.0")]
impl<I: fmt::Debug, St: fmt::Debug, F> fmt::Debug for Scan<I, St, F> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.debug_struct("Scan").field("iter", &self.iter).field("state", &self.state).finish()
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<B, I, St, F> Iterator for Scan<I, St, F>
where
I: Iterator,
F: FnMut(&mut St, I::Item) -> Option<B>,
{
type Item = B;
#[inline]
fn next(&mut self) -> Option<B> {
let a = self.iter.next()?;
(self.f)(&mut self.state, a)
}
#[inline]
fn size_hint(&self) -> (usize, Option<usize>) {
let (_, upper) = self.iter.size_hint();
(0, upper)
}
#[inline]
fn try_fold<Acc, Fold, R>(&mut self, init: Acc, fold: Fold) -> R
where
Self: Sized,
Fold: FnMut(Acc, Self::Item) -> R,
R: Try<Output = Acc>,
{
fn scan<'a, T, St, B, Acc, R: Try<Output = Acc>>(
state: &'a mut St,
f: &'a mut impl FnMut(&mut St, T) -> Option<B>,
mut fold: impl FnMut(Acc, B) -> R + 'a,
) -> impl FnMut(Acc, T) -> ControlFlow<R, Acc> + 'a {
move |acc, x| match f(state, x) {
None => ControlFlow::Break(try { acc }),
Some(x) => ControlFlow::from_try(fold(acc, x)),
}
}
let state = &mut self.state;
let f = &mut self.f;
self.iter.try_fold(init, scan(state, f, fold)).into_try()
}
#[inline]
fn fold<Acc, Fold>(mut self, init: Acc, fold: Fold) -> Acc
where
Self: Sized,
Fold: FnMut(Acc, Self::Item) -> Acc,
{
#[inline]
fn ok<B, T>(mut f: impl FnMut(B, T) -> B) -> impl FnMut(B, T) -> Result<B, !> {
move |acc, x| Ok(f(acc, x))
}
self.try_fold(init, ok(fold)).unwrap()
}
}
#[unstable(issue = "none", feature = "inplace_iteration")]
unsafe impl<St, F, I> SourceIter for Scan<I, St, F>
where
I: SourceIter,
{
type Source = I::Source;
#[inline]
unsafe fn as_inner(&mut self) -> &mut I::Source {
unsafe { SourceIter::as_inner(&mut self.iter) }
}
}
#[unstable(issue = "none", feature = "inplace_iteration")]
unsafe impl<St, F, B, I: InPlaceIterable> InPlaceIterable for Scan<I, St, F> where
F: FnMut(&mut St, I::Item) -> Option<B>
{
}