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use crate::fmt;
use crate::iter::{adapters::SourceIter, FusedIterator, 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 TakeWhile<I, P> {
iter: I,
flag: bool,
predicate: P,
}
impl<I, P> TakeWhile<I, P> {
pub(in crate::iter) fn new(iter: I, predicate: P) -> TakeWhile<I, P> {
TakeWhile { iter, flag: false, predicate }
}
}
#[stable(feature = "core_impl_debug", since = "1.9.0")]
impl<I: fmt::Debug, P> fmt::Debug for TakeWhile<I, P> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.debug_struct("TakeWhile").field("iter", &self.iter).field("flag", &self.flag).finish()
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<I: Iterator, P> Iterator for TakeWhile<I, P>
where
P: FnMut(&I::Item) -> bool,
{
type Item = I::Item;
#[inline]
fn next(&mut self) -> Option<I::Item> {
if self.flag {
None
} else {
let x = self.iter.next()?;
if (self.predicate)(&x) {
Some(x)
} else {
self.flag = true;
None
}
}
}
#[inline]
fn size_hint(&self) -> (usize, Option<usize>) {
if self.flag {
(0, Some(0))
} else {
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 check<'a, T, Acc, R: Try<Output = Acc>>(
flag: &'a mut bool,
p: &'a mut impl FnMut(&T) -> bool,
mut fold: impl FnMut(Acc, T) -> R + 'a,
) -> impl FnMut(Acc, T) -> ControlFlow<R, Acc> + 'a {
move |acc, x| {
if p(&x) {
ControlFlow::from_try(fold(acc, x))
} else {
*flag = true;
ControlFlow::Break(try { acc })
}
}
}
if self.flag {
try { init }
} else {
let flag = &mut self.flag;
let p = &mut self.predicate;
self.iter.try_fold(init, check(flag, p, 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()
}
}
#[stable(feature = "fused", since = "1.26.0")]
impl<I, P> FusedIterator for TakeWhile<I, P>
where
I: FusedIterator,
P: FnMut(&I::Item) -> bool,
{
}
#[unstable(issue = "none", feature = "inplace_iteration")]
unsafe impl<P, I> SourceIter for TakeWhile<I, P>
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<I: InPlaceIterable, F> InPlaceIterable for TakeWhile<I, F> where
F: FnMut(&I::Item) -> bool
{
}
