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Comment by darknoon | Hacker News Reader

This is not the same thing.

CACurrentMediaTime() / CFAbsoluteTimeGetCurrent() are first of all not deprecated (just check CFDate.h / CABase.h) but return a time interval since system boot so they are guaranteed to be increasing. It's just a fp64 representation of mach_absolute_time() without needing to worry about the time base vs seconds.

Date() / NSDate returns a wall clock time, which is less accurate and not guaranteed to increase uniformly (ie adjusting to time server, user changes time etc)

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Oops, you're right on the deprecation point. CFAbsoluteTimeGetCurrent is not itself deprecated but every method associated with it is [1].

Also CFAbsoluteTimeGetCurrent explicitly calls out that it isn't guaranteed to only increase. CACurrentMediaTime is monotonic though.

CFAbsoluteTimeGetCurrent also returns seconds since 2001 and is not monotonic, so there's really no reason to use it instead of Date().timeIntervalSinceReferenceDate. The most idiomatic equivalent to the Python time method is definitely some usage of Date(), as time in Python doesn't have monotonic guarantees either.

[1] https://developer.apple.com/documentation/corefoundation/154...

> CFAbsoluteTimeGetCurrent is not itself deprecated but every method associated with it is.

Because they deal with calendar-related stuff that is better accessed through Date.

”CACurrentMediaTime() / CFAbsoluteTimeGetCurrent() […] are guaranteed to be increasing.”

That is true for CACurrentMediaTime, but that time stops when the system sleeps (https://developer.apple.com/documentation/quartzcore/1395996... says it calls mach_absolute_time, and https://developer.apple.co/documentation/driverkit/3438076-m... says ” Returns current value of a clock that increments monotonically in tick units (starting at an arbitrary point), this clock does not increment while the system is asleep.”)

Also (https://developer.apple.com/documentation/corefoundation/154...):

Repeated calls to this function do not guarantee monotonically increasing results. The system time may decrease due to synchronization with external time references or due to an explicit user change of the clock.

Python's time.time() call is also going to be affected by system time changes and thus not guaranteed to increase uniformly. So Date() in Swift and time.time() in Python are the same in that regard.

Correct, the appropriate function is time.monotonic().

Python's time() call is returning the unix epoch wall clock time. Newbies (and most engineers TBH) are not going to know the subtleties and reasons why you'd use a monotonic clock or to even think of using one or another.

So for this comparison, it is better to use Date().

CFAbsoluteTimeGetCurrent() returns wall clock time, as far as I can tell the exact same thing as -[NSDate timeIntervalSinceReferenceDate].

https://developer.apple.com/documentation/corefoundation/154...

https://developer.apple.com/documentation/foundation/nsdate/...

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