Stopwatch

Standard library class · Made with Stopwatch.start()

A Stopwatch measures how long something takes. It reads the computer’s steady clock, which only moves forward, so a change to the computer’s date or time partway through can’t make a measurement wrong or negative. For the time of day, use Instant.now() instead.

const watch = Stopwatch.start()
var total = 0
for number in 1..100000 {
    total += number
}
print(total)
print(watch.elapsed() < Duration(seconds: 5))

Output

5000050000
true

A Stopwatch is a class rather than a value, since it is a running thing. Stopwatch() isn’t allowed; Emerald points you to Stopwatch.start(). A stopwatch prints as Stopwatch(1.25s), showing the time so far.

To pause a program rather than measure it, see Program.sleep.

At a glance

Making one
Stopwatch.start()	A stopwatch that starts now

Reading
elapsed()	The time since it started
restart()	Start measuring again from now

Making one

Stopwatch.start(): Stopwatch

A stopwatch that starts at once.

Reading

elapsed(): Duration

The time since the stopwatch started, or was last restarted, as a Duration. It is read afresh at each call, which is why it is a method with parentheses: its answer changes by itself.

const watch = Stopwatch.start()
const first = watch.elapsed()
const second = watch.elapsed()
print(second >= first)

Output

true

restart()

Starts measuring again from now, as if the stopwatch had just been made.

const watch = Stopwatch.start()
watch.restart()
print(watch.elapsed() < Duration(seconds: 5))

Output

true