NewCounter starts a new Counter.

NewUpdater starts a new Updater.

A Counter tracks a running count and controls a goroutine that passes its value periodically to a Func.

NoopPrinter discards all messages.

TestPrinter prints messages during testing.

An Updater controls a goroutine that periodically calls an UpdateFunc.

A Printer can can return a new counter or print messages at different log levels.

A Func is a callback for a Counter.

An UpdateFunc is a callback for a (progress) Updater.