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Retrieving attributed string attribute values should not use identity casts #1290

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merged 1 commit into from
May 14, 2025
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Retrieving attributed string attribute values should not use identity casts #1290

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14 changes: 8 additions & 6 deletions Sources/FoundationEssentials/AttributedString/AttributedStringAttributeStorage.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -54,18 +54,20 @@ extension AttributedString {
func rawValue<K: AttributedStringKey>(
as key: K.Type
) -> K.Value where K.Value: Sendable {
func extractValue<RealValue>(_ value: RealValue) -> K.Value {
assert(RealValue.self == K.Value.self, "_AttributeValue raw value can only be retrieved with a key whose value matches the stored attribute value (stored type \(RealValue.self) does not match key value type \(K.Value.self))")
return _identityCast(value, to: K.Value.self)
// Dynamic cast instead of an identity cast to support bridging between attribute value types like NSColor/UIColor
guard let value = self._rawValue as? K.Value else {
preconditionFailure("Unable to read \(K.self) attribute: stored value of type \(type(of: self._rawValue)) is not key's value type (\(K.Value.self))")
}
return _openExistential(self._rawValue, do: extractValue)
return value
}

static func ==(left: Self, right: Self) -> Bool {
func openEquatableLHS<LeftValue: Hashable & Sendable>(_ leftValue: LeftValue) -> Bool {
func openEquatableRHS<RightValue: Hashable & Sendable>(_ rightValue: RightValue) -> Bool {
assert(LeftValue.self == RightValue.self, "Two _AttributeValues can only be compared if they are of the same attribute value type")
let rightValueAsLeft = _identityCast(rightValue, to: LeftValue.self)
// Dynamic cast instead of an identity cast to support bridging between attribute value types like NSColor/UIColor
guard let rightValueAsLeft = rightValue as? LeftValue else {
return false
}
return rightValueAsLeft == leftValue
}
return openEquatableRHS(right._rawValue)
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