diff --git a/src/libcore/slice/mod.rs b/src/libcore/slice/mod.rs index acca9748372..b048a12e402 100644 --- a/src/libcore/slice/mod.rs +++ b/src/libcore/slice/mod.rs @@ -3835,6 +3835,19 @@ fn next_back(&mut self) -> Option<&'a [T]> { ret } } + + #[inline] + fn nth_back(&mut self, n: usize) -> Option { + let (end, overflow) = self.v.len().overflowing_sub(n); + if end < self.size || overflow { + self.v = &[]; + None + } else { + let ret = &self.v[end-self.size..end]; + self.v = &self.v[..end-1]; + Some(ret) + } + } } #[stable(feature = "rust1", since = "1.0.0")] diff --git a/src/libcore/tests/slice.rs b/src/libcore/tests/slice.rs index 04d646ea01d..1e92b6f7878 100644 --- a/src/libcore/tests/slice.rs +++ b/src/libcore/tests/slice.rs @@ -578,6 +578,19 @@ fn test_windows_nth() { assert_eq!(c2.next(), None); } +#[test] +fn test_windows_nth_back() { + let v: &[i32] = &[0, 1, 2, 3, 4, 5]; + let mut c = v.windows(2); + assert_eq!(c.nth_back(2).unwrap()[0], 2); + assert_eq!(c.next_back().unwrap()[1], 2); + + let v2: &[i32] = &[0, 1, 2, 3, 4]; + let mut c2 = v2.windows(4); + assert_eq!(c2.nth_back(1).unwrap()[1], 1); + assert_eq!(c2.next_back(), None); +} + #[test] fn test_windows_last() { let v: &[i32] = &[0, 1, 2, 3, 4, 5];