From 963bd3b643bae735cc46f8637e744163576244ea Mon Sep 17 00:00:00 2001
From: Ryan Lopopolo <rjl@hyperbo.la>
Date: Sat, 15 May 2021 10:37:05 -0700
Subject: [PATCH] Implement more Iterator methods on core::iter::Repeat
`core::iter::Repeat` always returns the same element, which means we can
do better than implementing most `Iterator` methods in terms of
`Iterator::next`.
Fixes #81292.
---
library/core/src/iter/sources/repeat.rs | 35 +++++++++++++++++++++++++
1 file changed, 35 insertions(+)
diff --git a/library/core/src/iter/sources/repeat.rs b/library/core/src/iter/sources/repeat.rs
index d1f2879235f1a..a9478041c69c4 100644
--- a/library/core/src/iter/sources/repeat.rs
+++ b/library/core/src/iter/sources/repeat.rs
@@ -72,10 +72,32 @@ impl<A: Clone> Iterator for Repeat<A> {
fn next(&mut self) -> Option<A> {
Some(self.element.clone())
}
+
#[inline]
fn size_hint(&self) -> (usize, Option<usize>) {
(usize::MAX, None)
}
+
+ #[inline]
+ fn advance_by(&mut self, n: usize) -> Result<(), usize> {
+ // Advancing an infinite iterator of a single element is a no-op.
+ let _ = n;
+ Ok(())
+ }
+
+ #[inline]
+ fn nth(&mut self, n: usize) -> Option<A> {
+ let _ = n;
+ Some(self.element.clone())
+ }
+
+ fn last(self) -> Option<A> {
+ loop {}
+ }
+
+ fn count(self) -> usize {
+ loop {}
+ }
}
#[stable(feature = "rust1", since = "1.0.0")]
@@ -84,6 +106,19 @@ impl<A: Clone> DoubleEndedIterator for Repeat<A> {
fn next_back(&mut self) -> Option<A> {
Some(self.element.clone())
}
+
+ #[inline]
+ fn advance_back_by(&mut self, n: usize) -> Result<(), usize> {
+ // Advancing an infinite iterator of a single element is a no-op.
+ let _ = n;
+ Ok(())
+ }
+
+ #[inline]
+ fn nth_back(&mut self, n: usize) -> Option<A> {
+ let _ = n;
+ Some(self.element.clone())
+ }
}
#[stable(feature = "fused", since = "1.26.0")]