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#[cfg(feature = "use_std")]
use std::error::Error;
use std::fmt::{Debug, Display, Formatter, Result as FmtResult};
use std::iter::ExactSizeIterator;
use either::Either;
use crate::size_hint;
/// Iterator returned for the error case of `IterTools::exactly_one()`
/// This iterator yields exactly the same elements as the input iterator.
///
/// During the execution of `exactly_one` the iterator must be mutated. This wrapper
/// effectively "restores" the state of the input iterator when it's handed back.
///
/// This is very similar to `PutBackN` except this iterator only supports 0-2 elements and does not
/// use a `Vec`.
#[derive(Clone)]
pub struct ExactlyOneError<I>
where
I: Iterator,
{
first_two: Option<Either<[I::Item; 2], I::Item>>,
inner: I,
}
impl<I> ExactlyOneError<I>
where
I: Iterator,
{
/// Creates a new `ExactlyOneErr` iterator.
pub(crate) fn new(first_two: Option<Either<[I::Item; 2], I::Item>>, inner: I) -> Self {
Self { first_two, inner }
}
fn additional_len(&self) -> usize {
match self.first_two {
Some(Either::Left(_)) => 2,
Some(Either::Right(_)) => 1,
None => 0,
}
}
}
impl<I> Iterator for ExactlyOneError<I>
where
I: Iterator,
{
type Item = I::Item;
fn next(&mut self) -> Option<Self::Item> {
match self.first_two.take() {
Some(Either::Left([first, second])) => {
self.first_two = Some(Either::Right(second));
Some(first)
},
Some(Either::Right(second)) => {
Some(second)
}
None => {
self.inner.next()
}
}
}
fn size_hint(&self) -> (usize, Option<usize>) {
size_hint::add_scalar(self.inner.size_hint(), self.additional_len())
}
}
impl<I> ExactSizeIterator for ExactlyOneError<I> where I: ExactSizeIterator {}
impl<I> Display for ExactlyOneError<I>
where I: Iterator,
{
fn fmt(&self, f: &mut Formatter) -> FmtResult {
let additional = self.additional_len();
if additional > 0 {
write!(f, "got at least 2 elements when exactly one was expected")
} else {
write!(f, "got zero elements when exactly one was expected")
}
}
}
impl<I> Debug for ExactlyOneError<I>
where I: Iterator + Debug,
I::Item: Debug,
{
fn fmt(&self, f: &mut Formatter) -> FmtResult {
match &self.first_two {
Some(Either::Left([first, second])) => {
write!(f, "ExactlyOneError[First: {:?}, Second: {:?}, RemainingIter: {:?}]", first, second, self.inner)
},
Some(Either::Right(second)) => {
write!(f, "ExactlyOneError[Second: {:?}, RemainingIter: {:?}]", second, self.inner)
}
None => {
write!(f, "ExactlyOneError[RemainingIter: {:?}]", self.inner)
}
}
}
}
#[cfg(feature = "use_std")]
impl<I> Error for ExactlyOneError<I> where I: Iterator + Debug, I::Item: Debug, {}