)
Creates a future that runs its computation after a delay.
The computation
will be executed after the given duration
has passed,
and the future is completed with the result.
If the duration is 0 or less,
it completes no sooner than in the next event-loop iteration.
If computation
is omitted,
it will be treated as if computation
was set to () => null
,
and the future will eventually complete with the null
value.
If calling computation
throws, the created future will complete with the
error.
See also Completer for a way to create and complete a future at a later time that isn't necessarily after a known fixed duration.