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Lazily compute whether attribute changed in _attributeModified(_:old:new:) #1237

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merged 1 commit into from
Apr 7, 2025
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Lazily compute whether attribute changed in _attributeModified(_:old:new:) #1237

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5 changes: 4 additions & 1 deletion Sources/FoundationEssentials/AttributedString/AttributedStringAttributeStorage.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -186,12 +186,15 @@ extension AttributedString._AttributeStorage {
invalidatableKeys.remove(key)
}

guard old != new else { return }
// Lazy to ensure we only check if the value changed when we actually need to because we found a dependent attribute
// Unboxing the attribute value to call its == implementation can be expensive, so for text that doesn't contain dependent attributes avoid it when possible
lazy var valueChanged = { old != new }()

for k in invalidatableKeys {
guard k != key else { continue }
guard let value = contents[k] else { continue }
guard value.isInvalidatedOnChange(of: key) else { continue }
guard valueChanged else { return }
// FIXME: ☠️ This subscript assignment is recursively calling this same method.
// FIXME: Collect invalidated keys into a temporary set instead, and progressively
// FIXME: extend that set until all its keys are gone.
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