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PeekNth: don't panic on peek_nth(usize::MAX) #1103

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PeekNth: don't panic on peek_nth(usize::MAX) #1103

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4 changes: 2 additions & 2 deletions src/peek_nth.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -69,7 +69,7 @@ where
/// assert_eq!(iter.peek_nth(1), None);
/// ```
pub fn peek_nth(&mut self, n: usize) -> Option<&I::Item> {
let unbuffered_items = (n + 1).saturating_sub(self.buf.len());
let unbuffered_items = n.checked_add(1)?.saturating_sub(self.buf.len());

self.buf.extend(self.iter.by_ref().take(unbuffered_items));

Expand Down Expand Up @@ -110,7 +110,7 @@ where
/// assert_eq!(iter.peek_nth_mut(1), None);
/// ```
pub fn peek_nth_mut(&mut self, n: usize) -> Option<&mut I::Item> {
let unbuffered_items = (n + 1).saturating_sub(self.buf.len());
let unbuffered_items = n.checked_add(1)?.saturating_sub(self.buf.len());

self.buf.extend(self.iter.by_ref().take(unbuffered_items));

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6 changes: 6 additions & 0 deletions tests/test_std.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -829,6 +829,12 @@ fn test_peek_nth() {

assert_eq!(iter.peek_nth(0), None);
assert_eq!(iter.peek_nth(1), None);

// Issue #1067: peek_nth(usize::MAX) used to panic in debug builds
// because of the n + 1 overflow. Should just return None now.
let mut iter = peek_nth(nums.iter().copied());
assert_eq!(iter.peek_nth(usize::MAX), None);
assert_eq!(iter.peek_nth_mut(usize::MAX), None);
}

#[test]
Expand Down