dcd643a652
`iter.last()` will drop all elements of `iter` in order, while `iter.next_back()` will drop the non-last elements of `iter` when `iter` goes out of scope since `.next_back()` does not consume its argument. When the transformation proposed by `double_ended_iterator_last` would concern an iterator whose element type has a significant drop, a note is added to warn about the possible drop order change, and the suggestion is switched from `MachineApplicable` to `MaybeIncorrect`.
92 lines
3 KiB
Rust
92 lines
3 KiB
Rust
#![warn(clippy::double_ended_iterator_last)]
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// Typical case
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pub fn last_arg(s: &str) -> Option<&str> {
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s.split(' ').next_back() //~ ERROR: called `Iterator::last` on a `DoubleEndedIterator`
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}
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fn main() {
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// General case
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struct DeIterator;
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impl Iterator for DeIterator {
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type Item = ();
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fn next(&mut self) -> Option<Self::Item> {
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Some(())
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}
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}
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impl DoubleEndedIterator for DeIterator {
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fn next_back(&mut self) -> Option<Self::Item> {
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Some(())
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}
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}
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let _ = DeIterator.next_back(); //~ ERROR: called `Iterator::last` on a `DoubleEndedIterator`
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// Should not apply to other methods of Iterator
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let _ = DeIterator.count();
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// Should not apply to simple iterators
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struct SimpleIterator;
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impl Iterator for SimpleIterator {
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type Item = ();
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fn next(&mut self) -> Option<Self::Item> {
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Some(())
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}
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}
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let _ = SimpleIterator.last();
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// Should not apply to custom implementations of last()
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struct CustomLast;
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impl Iterator for CustomLast {
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type Item = ();
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fn next(&mut self) -> Option<Self::Item> {
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Some(())
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}
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fn last(self) -> Option<Self::Item> {
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Some(())
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}
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}
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impl DoubleEndedIterator for CustomLast {
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fn next_back(&mut self) -> Option<Self::Item> {
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Some(())
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}
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}
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let _ = CustomLast.last();
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}
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fn issue_14139() {
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let mut index = [true, true, false, false, false, true].iter();
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let mut subindex = index.by_ref().take(3);
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let _ = subindex.next_back(); //~ ERROR: called `Iterator::last` on a `DoubleEndedIterator`
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let mut index = [true, true, false, false, false, true].iter();
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let mut subindex = index.by_ref().take(3);
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let _ = subindex.next_back(); //~ ERROR: called `Iterator::last` on a `DoubleEndedIterator`
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let mut index = [true, true, false, false, false, true].iter();
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let mut subindex = index.by_ref().take(3);
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let subindex = &mut subindex;
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let _ = subindex.next_back(); //~ ERROR: called `Iterator::last` on a `DoubleEndedIterator`
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let mut index = [true, true, false, false, false, true].iter();
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let mut subindex = index.by_ref().take(3);
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let subindex = &mut subindex;
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let _ = subindex.next_back(); //~ ERROR: called `Iterator::last` on a `DoubleEndedIterator`
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let mut index = [true, true, false, false, false, true].iter();
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let (mut subindex, _) = (index.by_ref().take(3), 42);
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let _ = subindex.next_back(); //~ ERROR: called `Iterator::last` on a `DoubleEndedIterator`
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}
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fn drop_order() {
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struct S(&'static str);
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impl std::ops::Drop for S {
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fn drop(&mut self) {
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println!("Dropping {}", self.0);
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}
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}
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let v = vec![S("one"), S("two"), S("three")];
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let mut v = v.into_iter();
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println!("Last element is {}", v.next_back().unwrap().0);
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//~^ ERROR: called `Iterator::last` on a `DoubleEndedIterator`
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println!("Done");
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}
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