diff options
| -rw-r--r-- | library/alloc/tests/slice.rs | 74 | ||||
| -rw-r--r-- | library/core/src/slice/iter.rs | 33 |
2 files changed, 99 insertions, 8 deletions
diff --git a/library/alloc/tests/slice.rs b/library/alloc/tests/slice.rs index 1fb4a51acfd..fe3d7183ee2 100644 --- a/library/alloc/tests/slice.rs +++ b/library/alloc/tests/slice.rs @@ -994,6 +994,80 @@ fn test_rsplitnator() { } #[test] +fn test_split_iterators_size_hint() { + for len in 0..=2 { + let mut v: Vec<u8> = (0..len).collect(); + fn verify_descending(sequence: &[usize], context: &str) { + let len = sequence.len(); + let target: Vec<usize> = (0..len).rev().collect(); + assert_eq!(sequence, target, "while testing: {}", context); + } + + macro_rules! test_size_hint { + ($create_iterator:expr) => {{ + // with a predicate always returning false, the split*-iterators + // become maximally short, so the size_hint lower bounds are correct + + macro_rules! p { + () => { + |_| false + }; + } + let mut short_iterator = $create_iterator; + let mut lower_bounds = vec![short_iterator.size_hint().0]; + while let Some(_) = short_iterator.next() { + lower_bounds.push(short_iterator.size_hint().0); + } + verify_descending(&lower_bounds, stringify!($create_iterator)); + } + { + // with a predicate always returning true, the split*-iterators + // become maximally long, so the size_hint upper bounds are correct + + macro_rules! p { + () => { + |_| true + }; + } + let mut long_iterator = $create_iterator; + let mut upper_bounds = vec![ + long_iterator.size_hint().1.expect("split*-methods have known upper bound"), + ]; + while let Some(_) = long_iterator.next() { + upper_bounds.push( + long_iterator.size_hint().1.expect("split*-methods have known upper bound"), + ); + } + verify_descending(&upper_bounds, stringify!($create_iterator)); + }}; + } + + test_size_hint!(v.split(p!())); + test_size_hint!(v.split_mut(p!())); + test_size_hint!(v.splitn(0, p!())); + test_size_hint!(v.splitn(1, p!())); + test_size_hint!(v.splitn(2, p!())); + test_size_hint!(v.splitn(3, p!())); + test_size_hint!(v.splitn_mut(0, p!())); + test_size_hint!(v.splitn_mut(1, p!())); + test_size_hint!(v.splitn_mut(2, p!())); + test_size_hint!(v.splitn_mut(3, p!())); + test_size_hint!(v.split_inclusive(p!())); + test_size_hint!(v.split_inclusive_mut(p!())); + test_size_hint!(v.rsplit(p!())); + test_size_hint!(v.rsplit_mut(p!())); + test_size_hint!(v.rsplitn(0, p!())); + test_size_hint!(v.rsplitn(1, p!())); + test_size_hint!(v.rsplitn(2, p!())); + test_size_hint!(v.rsplitn(3, p!())); + test_size_hint!(v.rsplitn_mut(0, p!())); + test_size_hint!(v.rsplitn_mut(1, p!())); + test_size_hint!(v.rsplitn_mut(2, p!())); + test_size_hint!(v.rsplitn_mut(3, p!())); + } +} + +#[test] fn test_windowsator() { let v = &[1, 2, 3, 4]; diff --git a/library/core/src/slice/iter.rs b/library/core/src/slice/iter.rs index d67af9cf668..c0dfba490ec 100644 --- a/library/core/src/slice/iter.rs +++ b/library/core/src/slice/iter.rs @@ -400,7 +400,13 @@ where #[inline] fn size_hint(&self) -> (usize, Option<usize>) { - if self.finished { (0, Some(0)) } else { (1, Some(self.v.len() + 1)) } + if self.finished { + (0, Some(0)) + } else { + // If the predicate doesn't match anything, we yield one slice. + // If it matches every element, we yield `len() + 1` empty slices. + (1, Some(self.v.len() + 1)) + } } } @@ -525,7 +531,14 @@ where #[inline] fn size_hint(&self) -> (usize, Option<usize>) { - if self.finished { (0, Some(0)) } else { (1, Some(self.v.len() + 1)) } + if self.finished { + (0, Some(0)) + } else { + // If the predicate doesn't match anything, we yield one slice. + // If it matches every element, we yield `len()` one-element slices, + // or a single empty slice. + (1, Some(cmp::max(1, self.v.len()))) + } } } @@ -647,8 +660,8 @@ where if self.finished { (0, Some(0)) } else { - // if the predicate doesn't match anything, we yield one slice - // if it matches every element, we yield len+1 empty slices. + // If the predicate doesn't match anything, we yield one slice. + // If it matches every element, we yield `len() + 1` empty slices. (1, Some(self.v.len() + 1)) } } @@ -763,9 +776,10 @@ where if self.finished { (0, Some(0)) } else { - // if the predicate doesn't match anything, we yield one slice - // if it matches every element, we yield len+1 empty slices. - (1, Some(self.v.len() + 1)) + // If the predicate doesn't match anything, we yield one slice. + // If it matches every element, we yield `len()` one-element slices, + // or a single empty slice. + (1, Some(cmp::max(1, self.v.len()))) } } } @@ -1008,7 +1022,10 @@ impl<T, I: SplitIter<Item = T>> Iterator for GenericSplitN<I> { #[inline] fn size_hint(&self) -> (usize, Option<usize>) { let (lower, upper_opt) = self.iter.size_hint(); - (lower, upper_opt.map(|upper| cmp::min(self.count, upper))) + ( + cmp::min(self.count, lower), + Some(upper_opt.map_or(self.count, |upper| cmp::min(self.count, upper))), + ) } } |