From 2b8991496226e736d96ef77193ba0595081284a4 Mon Sep 17 00:00:00 2001 From: Tim Vermeulen Date: Fri, 2 Oct 2020 02:46:19 +0200 Subject: [PATCH 1/3] Implement slice::{Iter, IterMut}::{advance_by, advance_back_by} Co-authored-by: The8472 --- library/core/src/slice/iter/macros.rs | 16 ++++++++++++++++ 1 file changed, 16 insertions(+) diff --git a/library/core/src/slice/iter/macros.rs b/library/core/src/slice/iter/macros.rs index 457b2a3605e8b..04945fa0e8211 100644 --- a/library/core/src/slice/iter/macros.rs +++ b/library/core/src/slice/iter/macros.rs @@ -185,6 +185,14 @@ macro_rules! iterator { } } + #[inline] + fn advance_by(&mut self, n: usize) -> Result<(), usize>{ + let advance = cmp::min(n, len!(self)); + // SAFETY: `advance` does not exceed `self.len()` by construction + unsafe { self.post_inc_start(advance as isize) }; + if advance == n { Ok(()) } else { Err(advance) } + } + #[inline] fn last(mut self) -> Option<$elem> { self.next_back() @@ -371,6 +379,14 @@ macro_rules! iterator { Some(next_back_unchecked!(self)) } } + + #[inline] + fn advance_back_by(&mut self, n: usize) -> Result<(), usize> { + let advance = cmp::min(n, len!(self)); + // SAFETY: `advance` does not exceed `self.len()` by construction + unsafe { self.pre_dec_end(advance as isize) }; + if advance == n { Ok(()) } else { Err(advance) } + } } #[stable(feature = "fused", since = "1.26.0")] From 5e90909f38d2921a463efea4a3656bc7a6c05709 Mon Sep 17 00:00:00 2001 From: Tim Vermeulen Date: Fri, 2 Oct 2020 02:47:01 +0200 Subject: [PATCH 2/3] Add tests --- library/core/src/slice/iter/macros.rs | 4 +-- library/core/tests/slice.rs | 42 +++++++++++++++++++++++++++ 2 files changed, 44 insertions(+), 2 deletions(-) diff --git a/library/core/src/slice/iter/macros.rs b/library/core/src/slice/iter/macros.rs index 04945fa0e8211..5434827e5dd0c 100644 --- a/library/core/src/slice/iter/macros.rs +++ b/library/core/src/slice/iter/macros.rs @@ -188,7 +188,7 @@ macro_rules! iterator { #[inline] fn advance_by(&mut self, n: usize) -> Result<(), usize>{ let advance = cmp::min(n, len!(self)); - // SAFETY: `advance` does not exceed `self.len()` by construction + // SAFETY: By construction, `advance` does not exceed `self.len()`. unsafe { self.post_inc_start(advance as isize) }; if advance == n { Ok(()) } else { Err(advance) } } @@ -383,7 +383,7 @@ macro_rules! iterator { #[inline] fn advance_back_by(&mut self, n: usize) -> Result<(), usize> { let advance = cmp::min(n, len!(self)); - // SAFETY: `advance` does not exceed `self.len()` by construction + // SAFETY: By construction, `advance` does not exceed `self.len()`. unsafe { self.pre_dec_end(advance as isize) }; if advance == n { Ok(()) } else { Err(advance) } } diff --git a/library/core/tests/slice.rs b/library/core/tests/slice.rs index 3a98cd9d2ee91..240b894057c3e 100644 --- a/library/core/tests/slice.rs +++ b/library/core/tests/slice.rs @@ -134,6 +134,48 @@ fn test_partition_point() { assert_eq!(b.partition_point(|&x| x < 8), 5); } +#[test] +fn test_iterator_advance_by() { + let v = &[0, 1, 2, 3, 4]; + + for i in 0..=v.len() { + let mut iter = v.iter(); + iter.advance_by(i).unwrap(); + assert_eq!(iter.as_slice(), &v[i..]); + } + + let mut iter = v.iter(); + assert_eq!(iter.advance_by(v.len() + 1), Err(v.len())); + assert_eq!(iter.as_slice(), &[]); + + let mut iter = v.iter(); + iter.advance_by(3).unwrap(); + assert_eq!(iter.as_slice(), &v[3..]); + iter.advance_by(2).unwrap(); + assert_eq!(iter.as_slice(), &[]); +} + +#[test] +fn test_iterator_advance_back_by() { + let v = &[0, 1, 2, 3, 4]; + + for i in 0..=v.len() { + let mut iter = v.iter(); + iter.advance_back_by(i).unwrap(); + assert_eq!(iter.as_slice(), &v[..v.len() - i]); + } + + let mut iter = v.iter(); + assert_eq!(iter.advance_back_by(v.len() + 1), Err(v.len())); + assert_eq!(iter.as_slice(), &[]); + + let mut iter = v.iter(); + iter.advance_back_by(3).unwrap(); + assert_eq!(iter.as_slice(), &v[..v.len() - 3]); + iter.advance_back_by(2).unwrap(); + assert_eq!(iter.as_slice(), &[]); +} + #[test] fn test_iterator_nth() { let v: &[_] = &[0, 1, 2, 3, 4]; From 5485f8a8ba7c4e2f9a01c3865b037c698887f317 Mon Sep 17 00:00:00 2001 From: Tim Vermeulen Date: Wed, 7 Oct 2020 12:48:08 +0200 Subject: [PATCH 3/3] Fix whitespace Co-authored-by: Ivan Tham --- library/core/src/slice/iter/macros.rs | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-) diff --git a/library/core/src/slice/iter/macros.rs b/library/core/src/slice/iter/macros.rs index 5434827e5dd0c..791a88dd97f28 100644 --- a/library/core/src/slice/iter/macros.rs +++ b/library/core/src/slice/iter/macros.rs @@ -185,8 +185,7 @@ macro_rules! iterator { } } - #[inline] - fn advance_by(&mut self, n: usize) -> Result<(), usize>{ + fn advance_by(&mut self, n: usize) -> Result<(), usize> { let advance = cmp::min(n, len!(self)); // SAFETY: By construction, `advance` does not exceed `self.len()`. unsafe { self.post_inc_start(advance as isize) };