[英]Dates are not equal while using timeIntervalSince1970
I've just run the code below several times and see that sometimes date1 and date2 are equal but sometimes are not.我刚刚运行了几次下面的代码,发现有时 date1 和 date2 相等,但有时不相等。
let date1 = Date()
let date2 = Date(timeIntervalSince1970: date1.timeIntervalSince1970)
print(date1)
print(date2)
print(date1.timeIntervalSince1970)
print(date2.timeIntervalSince1970)
print(date1 == date2)
So sometimes I get:所以有时我会得到:
2019-03-22 05:52:30 +0000
2019-03-22 05:52:30 +0000
1553233950.498001
1553233950.498001
false
These dates look the same but comparison tells me they are different.这些日期看起来相同,但比较告诉我它们是不同的。 The problem is that the date2 is slightly different from the date1.
问题是 date2 与 date1 略有不同。 To prove it I can write:
为了证明这一点,我可以写:
print(date1.timeIntervalSince(date2))
and get:并得到:
-1.1920928955078125e-07 -1.1920928955078125e-07
So it there any way to translate date1 to number and then back to date2 which is equal to date1?那么有什么方法可以将 date1 转换为数字,然后再返回到等于 date1 的 date2?
The problem is the usage of timeIntervalSince1970
.问题是
timeIntervalSince1970
的使用。 If you use this, the Date
implementation will do some Double
calculations to align it to the reference date (2001-01-01).如果您使用它,
Date
实现将进行一些Double
计算以将其与参考日期 (2001-01-01) 对齐。
If you use timeIntervalSinceReferenceDate
instead, this will be used directly, and your code should work then:如果您改用
timeIntervalSinceReferenceDate
,这将直接使用,您的代码应该可以工作:
for i in 1...200000 {
let date1 = Date()
let date2 = Date(timeIntervalSinceReferenceDate: date1.timeIntervalSinceReferenceDate)
if (date1 != date2) {
// never called on my machine:
let delta = date1.timeIntervalSince(date2)
print("\(i): \(delta)")
}
}
For your information, here the interesting parts of struct Date
implementation on https://github.com/apple/swift-corelibs-foundation/blob/master/Foundation/Date.swift - you see the calculation done in the first init
:供您参考,这里是https://github.com/apple/swift-corelibs-foundation/blob/master/Foundation/Date.swift上
struct Date
实现的有趣部分 - 您会看到在第一个init
完成的计算:
public struct Date : ReferenceConvertible, Comparable, Equatable {
fileprivate var _time: TimeInterval
public static let timeIntervalBetween1970AndReferenceDate: TimeInterval = 978307200.0
public init(timeIntervalSince1970: TimeInterval) {
self.init(timeIntervalSinceReferenceDate: timeIntervalSince1970 - Date.timeIntervalBetween1970AndReferenceDate)
}
public init(timeIntervalSinceReferenceDate ti: TimeInterval) {
_time = ti
}
}
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