[Merged by Bors] - Remove broken DoubleEndedIterator impls on event iterators
#7469
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Not super sure what to write for the Migration Guide |
tim-blackbird
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Feb 2, 2023
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| if scale_factor_events.iter().next_back().is_some() || ui_scale.is_changed() { | ||
| if !scale_factor_events.is_empty() || ui_scale.is_changed() { | ||
| scale_factor_events.clear(); |
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.next_back().is_some() wasn't the right way to do this, but unless multiple scale_factor_events are sent in a frame it behaves the same way as is_empty with a clear.
Not a big deal.
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The `DoubleEndedIterator` impls produce incorrect results on subsequent calls to `iter()` if the iterator is only partially consumed.
The following code shows what happens
```rust
fn next_back_is_bad() {
let mut events = Events::<TestEvent>::default();
events.send(TestEvent { i: 0 });
events.send(TestEvent { i: 1 });
events.send(TestEvent { i: 2 });
let mut reader = events.get_reader();
let mut iter = reader.iter(&events);
assert_eq!(iter.next_back(), Some(&TestEvent { i: 2 }));
assert_eq!(iter.next(), Some(&TestEvent { i: 0 }));
let mut iter = reader.iter(&events);
// `i: 2` event is returned twice! The `i: 1` event is missed.
assert_eq!(iter.next(), Some(&TestEvent { i: 2 }));
assert_eq!(iter.next(), None);
}
```
I don't think this can be fixed without adding some very convoluted bookkeeping.
## Migration Guide
`ManualEventIterator` and `ManualEventIteratorWithId` are no longer `DoubleEndedIterator`s.
Co-authored-by: devil-ira <[email protected]>
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The `DoubleEndedIterator` impls produce incorrect results on subsequent calls to `iter()` if the iterator is only partially consumed.
The following code shows what happens
```rust
fn next_back_is_bad() {
let mut events = Events::<TestEvent>::default();
events.send(TestEvent { i: 0 });
events.send(TestEvent { i: 1 });
events.send(TestEvent { i: 2 });
let mut reader = events.get_reader();
let mut iter = reader.iter(&events);
assert_eq!(iter.next_back(), Some(&TestEvent { i: 2 }));
assert_eq!(iter.next(), Some(&TestEvent { i: 0 }));
let mut iter = reader.iter(&events);
// `i: 2` event is returned twice! The `i: 1` event is missed.
assert_eq!(iter.next(), Some(&TestEvent { i: 2 }));
assert_eq!(iter.next(), None);
}
```
I don't think this can be fixed without adding some very convoluted bookkeeping.
## Migration Guide
`ManualEventIterator` and `ManualEventIteratorWithId` are no longer `DoubleEndedIterator`s.
Co-authored-by: devil-ira <[email protected]>
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Pull request successfully merged into main. Build succeeded:
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bors
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DoubleEndedIterator impls on event iteratorsDoubleEndedIterator impls on event iterators
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Feb 16, 2023
# Objective Motivated by #7469. `EventReader` iterators use the default implementations for `.nth()` and `.last()`, which includes iterating over and throwing out all events before the desired one. ## Solution Add specialized implementations for these methods that directly updates the unread event counter and returns a reference to the desired event. TODO: - [x] Add a unit test. - [x] ~~Add a benchmark, to see if the compiler was doing this automatically already.~~ *On second thought, this doesn't feel like a very useful thing to include in the benchmark suite.*
myreprise1
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Feb 18, 2023
# Objective Motivated by bevyengine#7469. `EventReader` iterators use the default implementations for `.nth()` and `.last()`, which includes iterating over and throwing out all events before the desired one. ## Solution Add specialized implementations for these methods that directly updates the unread event counter and returns a reference to the desired event. TODO: - [x] Add a unit test. - [x] ~~Add a benchmark, to see if the compiler was doing this automatically already.~~ *On second thought, this doesn't feel like a very useful thing to include in the benchmark suite.*
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The
DoubleEndedIteratorimpls produce incorrect results on subsequent calls toiter()if the iterator is only partially consumed.The following code shows what happens
I don't think this can be fixed without adding some very convoluted bookkeeping.
Migration Guide
ManualEventIteratorandManualEventIteratorWithIdare no longerDoubleEndedIterators.