Align Heap._UnsafeHandle min/maxValue tie-breaking with Swift.min/max#455
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lorentey merged 4 commits intoapple:mainfrom May 16, 2025
Merged
Align Heap._UnsafeHandle min/maxValue tie-breaking with Swift.min/max#455lorentey merged 4 commits intoapple:mainfrom
lorentey merged 4 commits intoapple:mainfrom
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lorentey
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May 2, 2025
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Thanks -- this is definitely a good idea.
The goal of this is to guarantee that Heap behaves in a specific way for equal-but-distinguishable elements. This new guarantee must come with tests that verify that the implementation behaves as expected; otherwise the bug we want to fix could be accidentally revived in future package releases.
| @inlinable @inline(__always) | ||
| internal func minValue(_ a: _HeapNode, _ b: _HeapNode) -> _HeapNode { | ||
| self[a] < self[b] ? a : b | ||
| self[a] <= self[b] ? a : b |
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I think it would make sense to add a comment explaining that the result emulates the stdlib. The implementation should also match precisely what the stdlib does, to emphasize this even further.
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| self[a] <= self[b] ? a : b | |
| // The expression used here matches the implementation of the | |
| // standard `Swift.min(_:_:)` function. This attempts to | |
| // preserve any pre-existing order in case `T` has identity. | |
| // `(min(x, y), max(x, y))` should return `(x, y)` in case `x == y`. | |
| self[b] < self[a] ? b : a |
| @inlinable @inline(__always) | ||
| internal func maxValue(_ a: _HeapNode, _ b: _HeapNode) -> _HeapNode { | ||
| self[a] < self[b] ? b : a | ||
| self[a] > self[b] ? a : b |
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| self[a] > self[b] ? a : b | |
| // In case `a` and `b` match, we need to pick `b`. See `minValue(_:_:)`. | |
| self[b] >= self[a] ? b : a |
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Sounds good, thanks for the revision. Will go ahead and also add those tests. |
…xpectations The existing expressions had the same effect, but they used different operators (`<=` instead of `<` and `>` instead of `>=`). The distinction is usually irrelevant, but there is no reason not to just follow what the stdlib is doing exactly.
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@swift-ci test |
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Heap._UnsafeHandle has minValue and maxValue. Original functionality was
minValue,if a == b, return b. FormaxValue,if a == b, return a. In both cases, this is the opposite tiebreaker choice fromSwift.minandSwift.max.Heap.replaceMaxusedHeap._UnsafeHandle.maxValuewhileHeap.maxusedSwift.max, and due to different tiebreaker choices, led to inconsistency as seen in #439 .Therefore I go ahead and update
Heap._UnsafeHandle.maxValue/minValueto be consistent withSwift.max/min.Fixes #439
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