当我尝试更改闭包中的变量时出现此错误:ACfunctionpointercannotbeformedfromaclosurethatcapturescontext是否有变通办法，或者仍然可以更改闭包中的变量？我的代码:letcallback:@convention(c)(readStream:CFWriteStream!,event:CFStreamEventType,data:UnsafeMutablePointer)->Void={(readStream,event,data)->Voidinswitchevent{caseCFStreamEventType.ErrorOccurr