Swift里字符串（二）创建

&＃xfffc;

最终都要走到__StringStorage 的 create(realCodeUnitCapacity,countAndFlags) 方法里去。

默认实现是 UTF8

internal static func _fromCodeUnits(_ input: Input,encoding: Encoding.Type,repair: Bool) -> (String, repairsMade: Bool)?where Input.Element &＃61;&＃61; Encoding.CodeUnit {// TODO(String Performance): Attempt to form smol strings// TODO(String performance): Skip intermediary array, transcode directly// into a StringStorage space.var contents: [UInt8] &＃61; []contents.reserveCapacity(input.underestimatedCount)let repaired &＃61; transcode(input.makeIterator(),from: Encoding.self,to: UTF8.self,stoppingOnError: false,into: { contents.append($0) })guard repair || !repaired else { return nil }let str &＃61; contents.withUnsafeBufferPointer { String._uncheckedFromUTF8($0) }return (str, repaired)}


可以看到&＃xff0c;把其他的编码方式&＃xff0c;都转为了UTF8&＃xff0c;然后编码后的缓存序列去创建了一个__StringStorage

&＃64;usableFromInlineinternal static func _uncheckedFromUTF8(_ input: UnsafeBufferPointer, asciiPreScanResult: Bool) -> String {if let smol &＃61; _SmallString(input) {return String(_StringGuts(smol))}let isASCII &＃61; asciiPreScanResultlet storage &＃61; __StringStorage.create(initializingFrom: input, isASCII: isASCII)return storage.asString}


在创建过程中&＃xff0c;又判断是否是_SmallString。