I’m working on an app, which displays a stopwatch on one of the views. To display stopwatch in a consistent way, values of minutes, seconds and milliseconds need proper amount of leading zeros. For example, values like `1 minute, 2 seconds, 3 milliseconds` should be displayed as `"01:02.003"`. There are two common ways of formatting numbers in Swift. However, one of them lead me to unexpected memory leak in my app.