system.time

system.time splits time into three types so that a duration can never be confused with a point in time, and neither can be confused with a bare number. A Clock is the capability for reading the wall clock and for sleeping.

use system.io
use system.time

fn main()
    // Clock is the capability for reading the wall clock and sleeping.
    let clock = Clock()

    // Duration is built through static constructors, never a bare number,
    // so the unit is always visible at the call site.
    let pause = Duration.from_millis(50)
    println(f"pausing for {pause.as_millis()} ms")

    let started = clock.now()
    clock.sleep(pause)

    // An Instant measures against the clock it was taken from.
    let taken = started.elapsed(clock)
    println(f"slept at least 50 ms: {taken.as_millis() >= 50}")

    println(f"{Duration.from_seconds(2).as_millis()} ms in two seconds")

Member	Returns	Behaviour
`Duration.from_nanos` / `from_micros` / `from_millis` / `from_seconds`	`Duration`	Static constructors — the unit is named at the call site, never implied.
`as_nanos()` / `as_micros()` / `as_millis()` / `as_seconds()`	`int`	Reads a `Duration` back in a chosen unit.
`Clock().now()`	`Instant`	A point in time.
`Clock().sleep(d Duration)`	—	Blocks for at least `d`.
`Instant.elapsed(clock Clock)`	`Duration`	Time since the instant was taken.

Those static constructors are what made Duration.from_millis(500) possible: static class members shipped as the language feature this module needed.