dispatch_after(dispatch_time(disPATCH_TIME_Now,10 * NSEC_PER_SEC),dispatch_get_main_queue(),{ doSomething() })
导致错误:“无法找到接受提供的参数的’*’的重载”.
NSEC_PER_SEC是一个UInt64,因此可以进行一些实验:
let x:UInt64 = 1000let m:Int64 = 10 * x
导致与上述相同的错误
let x:UInt64 = 1000let m:Int64 = 10 * (Int64) x
结果“一行上的连续陈述必须以’;’分隔”
let x:UInt64 = 1000let m:Int64 = 10 * ((Int64) x)
结果“预期”,“分隔符”
let x:UInt64 = 1000let m:Int64 = (Int64)10 * (Int64) x
结果“一行上的连续陈述必须以’;’分隔”
等等
该死的Swift编译器,我放弃了.如何将UInt64转换为Int64,和/或如何在swift中使用dispatch_time?
将UInt64转换为Int64是不安全的,因为UInt64的数字可能大于Int64.max,这将导致溢出.这是一个用于将UInt64转换为Int64的片段,反之亦然:
// Extension for 64-bit integer signed <-> unsigned conversionextension Int64 { var unsigned: UInt64 { let valuePointer = UnsafeMutablePointer<Int64>.allocate(capacity: 1) defer { valuePointer.deallocate(capacity: 1) } valuePointer.pointee = self return valuePointer.withMemoryRebound(to: UInt64.self,capacity: 1) {if currentValue < 0 { return Int64.max + currentValue + 1} else { return currentValue}.pointee } }}extension UInt64 { var signed: Int64 { let valuePointer = UnsafeMutablePointer<UInt64>.allocate(capacity: 1) defer { valuePointer.deallocate(capacity: 1) } valuePointer.pointee = self return valuePointer.withMemoryRebound(to: Int64.self,capacity: 1) {// Using an 8-bit integer for simplicity// currentValue0b1111_1111 // If this is interpreted as Int8,this is -1.// Strip sign bit0b0111_1111 // As Int8,this is 127. To get this we can add Int8.max// Int8.max + currentValue + 1127 + (-1) + 1 = 127.pointee } }}
这简单地将UInt64的二进制数据解释为Int64,即大于Int64.max的数字将是负的,因为64位整数的最高位的符号位.
如果你只想要正整数,那就得到绝对值.
编辑:根据行为,您可以获得绝对值,或:
后一种选择类似于剥离符号位.例如:
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