试图在Swift中调用dispatch_time正在努力,这就是为什么：
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 = 1000 let m:Int64 = 10 * x
导致与上述相同的错误
let x:UInt64 = 1000 let m:Int64 = 10 * (Int64) x
结果“一行上的连续陈述必须以’;’分隔”
let x:UInt64 = 1000 let m:Int64 = 10 * ((Int64) x)
结果“预期”,“分隔符”
let x:UInt64 = 1000 let 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.
原文链接：https://www.f2er.com/swift/319939.html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 conversion
extension 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) { $0.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) { $0.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：
if currentValue < 0 {
return Int64.max + currentValue + 1
} else {
return currentValue
}
后一种选择类似于剥离符号位.例如：
// Using an 8-bit integer for simplicity // currentValue 0b1111_1111 // If this is interpreted as Int8,this is -1. // Strip sign bit 0b0111_1111 // As Int8,this is 127. To get this we can add Int8.max // Int8.max + currentValue + 1 127 + (-1) + 1 = 127
