Swift Why isn't my date object that's (Equatable) equal after converting it to a string and back?

Question

I'm writing a unit test to check that my conversion from a date to string and back is successful.

I convert it to a string via:

func convertDateToString(date: Date) -> String {
    let dateFormatter = DateFormatter()
    dateFormatter.dateFormat = "yyyy-MM-dd HH:mm:ss"
    return dateFormatter.string(from: date)
}

and convert it back via:

func convertStringToDate(string: String) -> Date {
    let dateFormatter = DateFormatter()
    dateFormatter.dateFormat = "yyyy-MM-dd HH:mm:ss"
    return dateFormatter.date(from: string)!
}

If you try to use the Equatable protocol on the pre-conversion date and post-conversion date it says they are not the same. However, if you convert both pre and post dates to strings and compare them, they are Equatable. This is what it says when I run XCAssertEqual on pre and post dates:

XCTAssertEqual failed: ("2020-01-22 19:35:40 +0000") is not equal to ("2020-01-22 19:35:40 +0000")

Which looks pretty identical to me. I even tried converting the pre-conversion date to a string and back to check if the dates were equal and they still weren't

It's definitely `Equatable`, it's just not equal. – Alexander Jan 22 '20 at 20:51 — Alexander, Jan 22 '20 at 20:51
@Alexander-ReinstateMonica very good point. – Ian Kohlert Jan 23 '20 at 16:15 — Ian Kohlert, Jan 23 '20 at 16:15

Leo Dabus · Accepted Answer · 2020-02-09T14:14:08.050

8

The problem there is that Date is stored as a FloatingPoint value (timeIntervalSinceReferenceDate). There is fractional seconds being discarded there when converting your Date to String and back to Date. Take a look at post.

edited Feb 09 '20 at 14:14

answered Jan 22 '20 at 19:47

Leo Dabus

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Swift Why isn't my date object that's (Equatable) equal after converting it to a string and back?

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