#[inline]
fn spec_next(&mut self) -> Option<Self::Item> {
self.first_take = false;
- if self.iter.is_empty() {
- self.iter.is_iterating = Some(false);
+ self.iter.compute_is_empty();
+ if self.iter.is_empty.unwrap_or_default() {
return None;
}
// add 1 to self.step to get original step size back
// it was decremented for the general case on construction
if let Some(n) = self.iter.start.add_usize(self.step+1) {
- self.iter.is_iterating = Some(n <= self.iter.end);
+ self.iter.is_empty = Some(!(n <= self.iter.end));
let next = mem::replace(&mut self.iter.start, n);
Some(next)
} else {
let last = self.iter.start.clone();
- self.iter.is_iterating = Some(false);
+ self.iter.is_empty = Some(true);
Some(last)
}
}
#[inline]
fn next(&mut self) -> Option<A> {
- if self.is_empty() {
- self.is_iterating = Some(false);
+ self.compute_is_empty();
+ if self.is_empty.unwrap_or_default() {
return None;
}
- if self.start < self.end {
+ let is_iterating = self.start < self.end;
+ self.is_empty = Some(!is_iterating);
+ Some(if is_iterating {
let n = self.start.add_one();
- self.is_iterating = Some(true);
- Some(mem::replace(&mut self.start, n))
+ mem::replace(&mut self.start, n)
} else {
- self.is_iterating = Some(false);
- Some(self.start.clone())
- }
+ self.start.clone()
+ })
}
#[inline]
#[inline]
fn nth(&mut self, n: usize) -> Option<A> {
- if self.is_empty() {
- self.is_iterating = Some(false);
+ self.compute_is_empty();
+ if self.is_empty.unwrap_or_default() {
return None;
}
match plus_n.partial_cmp(&self.end) {
Some(Less) => {
- self.is_iterating = Some(true);
+ self.is_empty = Some(false);
self.start = plus_n.add_one();
return Some(plus_n)
}
Some(Equal) => {
- self.is_iterating = Some(false);
+ self.is_empty = Some(true);
return Some(plus_n)
}
_ => {}
}
}
- self.is_iterating = Some(false);
+ self.is_empty = Some(true);
None
}
impl<A: Step> DoubleEndedIterator for ops::RangeInclusive<A> {
#[inline]
fn next_back(&mut self) -> Option<A> {
- if self.is_empty() {
- self.is_iterating = Some(false);
+ self.compute_is_empty();
+ if self.is_empty.unwrap_or_default() {
return None;
}
- if self.start < self.end {
+ let is_iterating = self.start < self.end;
+ self.is_empty = Some(!is_iterating);
+ Some(if is_iterating {
let n = self.end.sub_one();
- self.is_iterating = Some(true);
- Some(mem::replace(&mut self.end, n))
+ mem::replace(&mut self.end, n)
} else {
- self.is_iterating = Some(false);
- Some(self.end.clone())
- }
+ self.end.clone()
+ })
}
}
pub struct RangeInclusive<Idx> {
pub(crate) start: Idx,
pub(crate) end: Idx,
- pub(crate) is_iterating: Option<bool>,
+ pub(crate) is_empty: Option<bool>,
// This field is:
// - `None` when next() or next_back() was never called
- // - `Some(true)` when `start <= end` assuming no overflow
- // - `Some(false)` otherwise
+ // - `Some(false)` when `start <= end` assuming no overflow
+ // - `Some(true)` otherwise
// The field cannot be a simple `bool` because the `..=` constructor can
// accept non-PartialOrd types, also we want the constructor to be const.
}
impl<T> RangeInclusiveEquality for T {
#[inline]
default fn canonicalized_is_empty(range: &RangeInclusive<Self>) -> bool {
- !range.is_iterating.unwrap_or(false)
+ range.is_empty.unwrap_or_default()
}
}
impl<T: PartialOrd> RangeInclusiveEquality for T {
#[stable(feature = "inclusive_range_methods", since = "1.27.0")]
#[inline]
pub const fn new(start: Idx, end: Idx) -> Self {
- Self { start, end, is_iterating: None }
+ Self { start, end, is_empty: None }
}
/// Returns the lower bound of the range (inclusive).
#[unstable(feature = "range_is_empty", reason = "recently added", issue = "48111")]
#[inline]
pub fn is_empty(&self) -> bool {
- !self.is_iterating.unwrap_or_else(|| self.start <= self.end)
+ self.is_empty.unwrap_or_else(|| !(self.start <= self.end))
+ }
+
+ // If this range's `is_empty` is field is unknown (`None`), update it to be a concrete value.
+ #[inline]
+ pub(crate) fn compute_is_empty(&mut self) {
+ if self.is_empty.is_none() {
+ self.is_empty = Some(!(self.start <= self.end));
+ }
}
}