所以我的问题是为什么let_=this比this!=nil快？例子:这是:letthis:Bool?=true//letstart=DispatchTime.now()for_in0...100000000{guardthis!=nilelse{continue}}letend=DispatchTime.now()letnanoTime=end.uptimeNanoseconds-start.uptimeNanosecondslettimeInterval=Double(nanoTime)print("Time\(timeInterval)")//Time5426559135.0//T