Swift⾥字符串（⼗⼀）OC字符串和Swift字符串的转换
to OC
func _bridgeToObjectiveCImpl() -> AnyObject {
if _guts.isSmall {
return _guts.asSmall.withUTF8 { bufPtr in
// TODO(String bridging): worth isASCII check for different encoding?
return _swift_stdlib_CFStringCreateWithBytes(
nil, bufPtr.baseAddress._unsafelyUnwrappedUnchecked,
kCFStringEncodingUTF8, 0)
as AnyObject
swift 字符串转数组
}
}
if _guts._object.isImmortal {
// TODO: We'd rather emit a valid ObjC object statically than create a
// shared string class instance.
let gutsCountAndFlags = _guts._object._countAndFlags
return __SharedStringStorage(
immortal: _guts._object.fastUTF8.baseAddress!,
countAndFlags: _StringObject.CountAndFlags(
sharedCount: _unt, isASCII: gutsCountAndFlags.isASCII))
}
_internalInvariant(_guts._object.hasObjCBridgeableObject,
"Unknown non-bridgeable object case")
return _guts._object.objCBridgeableObject
}
}
可以看到，如果String是不可变的，那么转到NSString会有⼀次内存 copy 操作。
Because NSString is immutable, it is just as though the storage was shared by a copy. The first in any sequence of mutating operations causes elements to be copied into unique, contiguous storage which may cost O(n) time and space, where n is the length of the string’s encoded representation (or more, if the underlying NSString has unusual performance characteristics).

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