From 5b834eb7943948cffa4d2af39762e4de30026d68 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} --- library/core/src/slice/iter/macros.rs | 41 +++++++-------------------- 1 file changed, 10 insertions(+), 31 deletions(-) diff --git a/library/core/src/slice/iter/macros.rs b/library/core/src/slice/iter/macros.rs index 457b2a3605e8b..a88faee90ccfa 100644 --- a/library/core/src/slice/iter/macros.rs +++ b/library/core/src/slice/iter/macros.rs @@ -163,26 +163,11 @@ macro_rules! iterator { } #[inline] - fn nth(&mut self, n: usize) -> Option<$elem> { - if n >= len!(self) { - // This iterator is now empty. - if mem::size_of::() == 0 { - // We have to do it this way as `ptr` may never be 0, but `end` - // could be (due to wrapping). - self.end = self.ptr.as_ptr(); - } else { - // SAFETY: end can't be 0 if T isn't ZST because ptr isn't 0 and end >= ptr - unsafe { - self.ptr = NonNull::new_unchecked(self.end as *mut T); - } - } - return None; - } - // SAFETY: We are in bounds. `post_inc_start` does the right thing even for ZSTs. - unsafe { - self.post_inc_start(n as isize); - Some(next_unchecked!(self)) - } + fn advance_by(&mut self, n: usize) -> Result<(), usize>{ + let advance = cmp::min(n, len!(self)); + // SAFETY: `advance` does not exceed `self.len()` by construction + unsafe { self.post_inc_start(advance as isize) }; + if advance == n { Ok(()) } else { Err(advance) } } #[inline] @@ -359,17 +344,11 @@ macro_rules! iterator { } #[inline] - fn nth_back(&mut self, n: usize) -> Option<$elem> { - if n >= len!(self) { - // This iterator is now empty. - self.end = self.ptr.as_ptr(); - return None; - } - // SAFETY: We are in bounds. `pre_dec_end` does the right thing even for ZSTs. - unsafe { - self.pre_dec_end(n as isize); - Some(next_back_unchecked!(self)) - } + 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) } } } From 3f22d0d9281acb05dac2b74eb44244ddf3e73c47 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 a88faee90ccfa..79513c1cd50a9 100644 --- a/library/core/src/slice/iter/macros.rs +++ b/library/core/src/slice/iter/macros.rs @@ -165,7 +165,7 @@ 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) } } @@ -346,7 +346,7 @@ 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 5ef30b1a8898a..f6b1d09ddbff5 100644 --- a/library/core/tests/slice.rs +++ b/library/core/tests/slice.rs @@ -122,6 +122,48 @@ 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 dd58782827d7763d4a569eac9ac0554dffaf114e 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 | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/library/core/src/slice/iter/macros.rs b/library/core/src/slice/iter/macros.rs index 79513c1cd50a9..be7d09e326031 100644 --- a/library/core/src/slice/iter/macros.rs +++ b/library/core/src/slice/iter/macros.rs @@ -163,7 +163,7 @@ 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) };