From db16e1721264dc06ac926a642deb4c7633a4b54d Mon Sep 17 00:00:00 2001 From: Kyle Huey Date: Tue, 2 Jul 2019 13:45:29 -0700 Subject: [PATCH] When possible without changing semantics, implement Iterator::last in terms of DoubleEndedIterator::next_back for types in liballoc and libcore. Provided that the iterator has finite length and does not trigger user-provided code, this is safe. What follows is a full list of the DoubleEndedIterators in liballoc/libcore and whether this optimization is safe, and if not, why not. src/liballoc/boxed.rs Box: Pass through to avoid defeating optimization of the underlying DoubleIterator implementation. This has no correctness impact. src/liballoc/collections/binary_heap.rs Iter: Pass through to avoid defeating optimizations on slice::Iter IntoIter: Not safe, changes Drop order Drain: Not safe, changes Drop order src/liballoc/collections/btree/map.rs Iter: Safe to call next_back, invokes no user defined code. IterMut: ditto IntoIter: Not safe, changes Drop order Keys: Safe to call next_back, invokes no user defined code. Values: ditto ValuesMut: ditto Range: ditto RangeMut: ditto src/liballoc/collections/btree/set.rs Iter: Safe to call next_back, invokes no user defined code. IntoIter: Not safe, changes Drop order Range: Safe to call next_back, invokes no user defined code. src/liballoc/collections/linked_list.rs Iter: Safe to call next_back, invokes no user defined code. IterMut: ditto IntoIter: Not safe, changes Drop order src/liballoc/collections/vec_deque.rs Iter: Safe to call next_back, invokes no user defined code. IterMut: ditto IntoIter: Not safe, changes Drop order Drain: ditto src/liballoc/string.rs Drain: Safe because return type is a primitive (char) src/liballoc/vec.rs IntoIter: Not safe, changes Drop order Drain: ditto Splice: ditto src/libcore/ascii.rs EscapeDefault: Safe because return type is a primitive (u8) src/libcore/iter/adapters/chain.rs Chain: Not safe, invokes user defined code (Iterator impl) src/libcore/iter/adapters/flatten.rs FlatMap: Not safe, invokes user defined code (Iterator impl) Flatten: ditto FlattenCompat: ditto src/libcore/iter/adapters/mod.rs Rev: Not safe, invokes user defined code (Iterator impl) Copied: ditto Cloned: Not safe, invokes user defined code (Iterator impl and T::clone) Map: Not safe, invokes user defined code (Iterator impl + closure) Filter: ditto FilterMap: ditto Enumerate: Not safe, invokes user defined code (Iterator impl) Skip: ditto Fuse: ditto Inspect: ditto src/libcore/iter/adapters/zip.rs Zip: Not safe, invokes user defined code (Iterator impl) src/libcore/iter/range.rs ops::Range: Not safe, changes Drop order, but ALREADY HAS SPECIALIZATION ops::RangeInclusive: ditto src/libcore/iter/sources.rs Repeat: Not safe, calling last should iloop. Empty: No point, iterator is at most one item long. Once: ditto OnceWith: ditto src/libcore/option.rs Item: No point, iterator is at most one item long. Iter: ditto IterMut: ditto IntoIter: ditto src/libcore/result.rs Iter: No point, iterator is at most one item long IterMut: ditto IntoIter: ditto src/libcore/slice/mod.rs Split: Not safe, invokes user defined closure SplitMut: ditto RSplit: ditto RSplitMut: ditto Windows: Safe, already has specialization Chunks: ditto ChunksMut: ditto ChunksExact: ditto ChunksExactMut: ditto RChunks: ditto RChunksMut: ditto RChunksExact: ditto RChunksExactMut: ditto src/libcore/str/mod.rs Chars: Safe, already has specialization CharIndices: ditto Bytes: ditto Lines: Safe to call next_back, invokes no user defined code. LinesAny: Deprecated Everything that is generic over P: Pattern: Not safe because Pattern invokes user defined code. SplitWhitespace: Safe to call next_back, invokes no user defined code. SplitAsciiWhitespace: ditto --- src/liballoc/boxed.rs | 8 +++++++ src/liballoc/collections/binary_heap.rs | 5 +++++ src/liballoc/collections/btree/map.rs | 28 +++++++++++++++++++++++++ src/liballoc/collections/btree/set.rs | 7 +++++++ src/liballoc/collections/linked_list.rs | 10 +++++++++ src/liballoc/collections/vec_deque.rs | 10 +++++++++ src/liballoc/string.rs | 5 +++++ src/libcore/ascii.rs | 1 + src/libcore/str/mod.rs | 15 +++++++++++++ 9 files changed, 89 insertions(+) diff --git a/src/liballoc/boxed.rs b/src/liballoc/boxed.rs index 9109a730cce2d..570e657b1015b 100644 --- a/src/liballoc/boxed.rs +++ b/src/liballoc/boxed.rs @@ -716,6 +716,14 @@ impl Iterator for Box { (**self).nth(n) } } + +#[stable(feature = "rust1", since = "1.0.0")] +impl Iterator for Box { + fn last(self) -> Option where I: Sized { + (*self).last() + } +} + #[stable(feature = "rust1", since = "1.0.0")] impl DoubleEndedIterator for Box { fn next_back(&mut self) -> Option { diff --git a/src/liballoc/collections/binary_heap.rs b/src/liballoc/collections/binary_heap.rs index c898f064fd09f..9f531f5b83c75 100644 --- a/src/liballoc/collections/binary_heap.rs +++ b/src/liballoc/collections/binary_heap.rs @@ -1035,6 +1035,11 @@ impl<'a, T> Iterator for Iter<'a, T> { fn size_hint(&self) -> (usize, Option) { self.iter.size_hint() } + + #[inline] + fn last(self) -> Option<&'a T> { + self.iter.last() + } } #[stable(feature = "rust1", since = "1.0.0")] diff --git a/src/liballoc/collections/btree/map.rs b/src/liballoc/collections/btree/map.rs index 6b079fc87cc78..8e1c870cf6b05 100644 --- a/src/liballoc/collections/btree/map.rs +++ b/src/liballoc/collections/btree/map.rs @@ -1193,6 +1193,10 @@ impl<'a, K: 'a, V: 'a> Iterator for Iter<'a, K, V> { fn size_hint(&self) -> (usize, Option) { (self.length, Some(self.length)) } + + fn last(mut self) -> Option<(&'a K, &'a V)> { + self.next_back() + } } #[stable(feature = "fused", since = "1.26.0")] @@ -1253,6 +1257,10 @@ impl<'a, K: 'a, V: 'a> Iterator for IterMut<'a, K, V> { fn size_hint(&self) -> (usize, Option) { (self.length, Some(self.length)) } + + fn last(mut self) -> Option<(&'a K, &'a mut V)> { + self.next_back() + } } #[stable(feature = "rust1", since = "1.0.0")] @@ -1421,6 +1429,10 @@ impl<'a, K, V> Iterator for Keys<'a, K, V> { fn size_hint(&self) -> (usize, Option) { self.inner.size_hint() } + + fn last(mut self) -> Option<&'a K> { + self.next_back() + } } #[stable(feature = "rust1", since = "1.0.0")] @@ -1458,6 +1470,10 @@ impl<'a, K, V> Iterator for Values<'a, K, V> { fn size_hint(&self) -> (usize, Option) { self.inner.size_hint() } + + fn last(mut self) -> Option<&'a V> { + self.next_back() + } } #[stable(feature = "rust1", since = "1.0.0")] @@ -1495,6 +1511,10 @@ impl<'a, K, V> Iterator for Range<'a, K, V> { unsafe { Some(self.next_unchecked()) } } } + + fn last(mut self) -> Option<(&'a K, &'a V)> { + self.next_back() + } } #[stable(feature = "map_values_mut", since = "1.10.0")] @@ -1508,6 +1528,10 @@ impl<'a, K, V> Iterator for ValuesMut<'a, K, V> { fn size_hint(&self) -> (usize, Option) { self.inner.size_hint() } + + fn last(mut self) -> Option<&'a mut V> { + self.next_back() + } } #[stable(feature = "map_values_mut", since = "1.10.0")] @@ -1626,6 +1650,10 @@ impl<'a, K, V> Iterator for RangeMut<'a, K, V> { unsafe { Some(self.next_unchecked()) } } } + + fn last(mut self) -> Option<(&'a K, &'a mut V)> { + self.next_back() + } } impl<'a, K, V> RangeMut<'a, K, V> { diff --git a/src/liballoc/collections/btree/set.rs b/src/liballoc/collections/btree/set.rs index 16a96ca19b824..d3af910a82c27 100644 --- a/src/liballoc/collections/btree/set.rs +++ b/src/liballoc/collections/btree/set.rs @@ -1019,6 +1019,9 @@ impl<'a, T> Iterator for Iter<'a, T> { fn size_hint(&self) -> (usize, Option) { self.iter.size_hint() } + fn last(mut self) -> Option<&'a T> { + self.next_back() + } } #[stable(feature = "rust1", since = "1.0.0")] impl<'a, T> DoubleEndedIterator for Iter<'a, T> { @@ -1073,6 +1076,10 @@ impl<'a, T> Iterator for Range<'a, T> { fn next(&mut self) -> Option<&'a T> { self.iter.next().map(|(k, _)| k) } + + fn last(mut self) -> Option<&'a T> { + self.next_back() + } } #[stable(feature = "btree_range", since = "1.17.0")] diff --git a/src/liballoc/collections/linked_list.rs b/src/liballoc/collections/linked_list.rs index 40a82d6feaa98..b5dbbe8fe2d01 100644 --- a/src/liballoc/collections/linked_list.rs +++ b/src/liballoc/collections/linked_list.rs @@ -832,6 +832,11 @@ impl<'a, T> Iterator for Iter<'a, T> { fn size_hint(&self) -> (usize, Option) { (self.len, Some(self.len)) } + + #[inline] + fn last(mut self) -> Option<&'a T> { + self.next_back() + } } #[stable(feature = "rust1", since = "1.0.0")] @@ -881,6 +886,11 @@ impl<'a, T> Iterator for IterMut<'a, T> { fn size_hint(&self) -> (usize, Option) { (self.len, Some(self.len)) } + + #[inline] + fn last(mut self) -> Option<&'a mut T> { + self.next_back() + } } #[stable(feature = "rust1", since = "1.0.0")] diff --git a/src/liballoc/collections/vec_deque.rs b/src/liballoc/collections/vec_deque.rs index 71faf672962b3..573dd86b23aeb 100644 --- a/src/liballoc/collections/vec_deque.rs +++ b/src/liballoc/collections/vec_deque.rs @@ -2206,6 +2206,11 @@ impl<'a, T> Iterator for Iter<'a, T> { self.tail = self.head - iter.len(); final_res } + + #[inline] + fn last(mut self) -> Option<&'a T> { + self.next_back() + } } #[stable(feature = "rust1", since = "1.0.0")] @@ -2319,6 +2324,11 @@ impl<'a, T> Iterator for IterMut<'a, T> { accum = front.iter_mut().fold(accum, &mut f); back.iter_mut().fold(accum, &mut f) } + + #[inline] + fn last(mut self) -> Option<&'a mut T> { + self.next_back() + } } #[stable(feature = "rust1", since = "1.0.0")] diff --git a/src/liballoc/string.rs b/src/liballoc/string.rs index 7f7722548f581..1b0d3c1969274 100644 --- a/src/liballoc/string.rs +++ b/src/liballoc/string.rs @@ -2385,6 +2385,11 @@ impl Iterator for Drain<'_> { fn size_hint(&self) -> (usize, Option) { self.iter.size_hint() } + + #[inline] + fn last(mut self) -> Option { + self.next_back() + } } #[stable(feature = "drain", since = "1.6.0")] diff --git a/src/libcore/ascii.rs b/src/libcore/ascii.rs index c0ab364380fbd..e6a6fdde54042 100644 --- a/src/libcore/ascii.rs +++ b/src/libcore/ascii.rs @@ -117,6 +117,7 @@ impl Iterator for EscapeDefault { type Item = u8; fn next(&mut self) -> Option { self.range.next().map(|i| self.data[i]) } fn size_hint(&self) -> (usize, Option) { self.range.size_hint() } + fn last(mut self) -> Option { self.next_back() } } #[stable(feature = "rust1", since = "1.0.0")] impl DoubleEndedIterator for EscapeDefault { diff --git a/src/libcore/str/mod.rs b/src/libcore/str/mod.rs index 34f2d8917ea47..f3fbf35181718 100644 --- a/src/libcore/str/mod.rs +++ b/src/libcore/str/mod.rs @@ -1333,6 +1333,11 @@ impl<'a> Iterator for Lines<'a> { fn size_hint(&self) -> (usize, Option) { self.0.size_hint() } + + #[inline] + fn last(mut self) -> Option<&'a str> { + self.next_back() + } } #[stable(feature = "rust1", since = "1.0.0")] @@ -4241,6 +4246,11 @@ impl<'a> Iterator for SplitWhitespace<'a> { fn size_hint(&self) -> (usize, Option) { self.inner.size_hint() } + + #[inline] + fn last(mut self) -> Option<&'a str> { + self.next_back() + } } #[stable(feature = "split_whitespace", since = "1.1.0")] @@ -4267,6 +4277,11 @@ impl<'a> Iterator for SplitAsciiWhitespace<'a> { fn size_hint(&self) -> (usize, Option) { self.inner.size_hint() } + + #[inline] + fn last(mut self) -> Option<&'a str> { + self.next_back() + } } #[stable(feature = "split_ascii_whitespace", since = "1.34.0")]