(clock)
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Clocks
In tick, clocks are used for getting the current time, in a given
time-zone. You should prefer using clocks to making direct calls to
(System/currentTimeMillis), because this then allows you and others
to plugin alternative clocks, perhaps for testing purposes.
You create a clock that tracks the current time.
With an argument, you can fix a clock to always report a fixed time.
(clock "1999-12-31T23:59:59")
Construction
| Code | Description | Return type |
|---|---|---|
(clock) | Return a clock that will always return the current time | java.time.Clock |
Derivation
Just like times and dates, you can time-shift clocks forward and
backward using the >> and << functions respectively.
(<< (clock) (hours 2))
You can also create a clock from a base clock which reports time with granualarity given by a duration.
(def minute-clk (tick (clock) (minutes 1)))
| Code | Description | Return type |
|---|---|---|
(<< (clock) (minutes 2)) | Return a clock running 2 minutes slow | java.time.Clock |
(>> (clock) (minutes 2)) | Return a clock running 2 minutes fast | java.time.Clock |
Comparison
| TBD |
Atomic clocks?
In Clojure, an atom is a holder of a value at a particular time. Similarly, a tick atom is a clock holding the clock’s time, which is constantly changing.
You create this atom with (atom). Naturally, you can get the instant of the atom’s clock by dereferencing, e.g. @(atom)
user> (def clk (atom)) user> (println @clk) #object[java.time.Instant 0x2e014670 2018-02-28T07:52:52.302Z] (some time later) user> (println @clk) #object[java.time.Instant 0x6e5b1dca 2018-02-28T08:01:50.622Z]
You can also create an atom with a clock.
(atom (clock))
| Code | Description | Return type |
|---|---|---|
(atom) | Return a clock that tracks the current time | java.time.Clock |
Substitution
A clock can be used to callibrate tick to a particular time and time-zone, if system defaults are not desired.
As I’m currently writing this in London, on my system I get the following when I use '(zone)'.
(zone) => #object[java.time.ZoneRegion 0x744a6545 "Europe/London"]
However, if we wanted to test in New York, we can set the clock to exist in that time-zone:
(t/with-clock (-> (t/clock) (t/in "America/New_York")) (t/zone)) => #object[java.time.ZoneRegion 0x5a9d412 "America/New_York"]
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