Factory書き換えのPRの一部を眺めた https://github.com/phausler/swift-corelibs-foundation/blob/e2f4b859a109adcaa91e3f0ebd4336a2e29c9fcb/Foundation/NSString.swift#L497

phausler/swift-corelibs-foundation

swift-corelibs-foundation - The Foundation Project, providing core utilities, internationalization, and OS independence

5:13 AM

URLがファイルじゃなかったらData読んできて2バイトだけみて UTF16 BOM検出して、 CFStringの関数で初期化して、最後に self.init(factory: _unsafeReferenceCast(cf, to: NSString.self)) で、 CFのオブジェクトで差し替え

5:14 AM

CFStringを _unsafeReferenceCast とやらで無理やりキャストしつつ、selfを差し替えるから

5:14 AM

Toll-Free Bridgeがここで仕込まれる

5:14 AM

よくうごくなあ・・・

5:19 AM

https://github.com/phausler/swift-corelibs-foundation/blob/01ac7af46bc353083dea8b9056a70d92576cfbb3/Foundation/NSString.swift#L1302

phausler/swift-corelibs-foundation

swift-corelibs-foundation - The Foundation Project, providing core utilities, internationalization, and OS independence

5:19 AM

そのパッチを当てる前の実装は謎だ

 guard let enc = enc, let cf = CFStringCreateWithBytes(kCFAllocatorDefault, bytePtr, readResult.length, CFStringConvertNSStringEncodingToEncoding(enc.pointee), true) else { throw NSError(domain: NSCocoaErrorDomain, code: CocoaError.fileReadInapplicableStringEncoding.rawValue, userInfo: [ "NSDebugDescription" : "Unable to create a string using the specified encoding." ]) } var str: String? if String._conditionallyBridgeFromObjectiveC(cf._nsObject, result: &str) { self.init(str!) } else {

(edited)

5:20 AM

cfのオブジェクトを作ったあと、_conditionallyBridgeFromObjectiveCで CFStringを Swift.String にキャスト？して

5:20 AM

self.init(String) に渡してる