Unexplained numeric literal

Reports a numeric literal of three or more digits used directly as the initialiser of a val or var, where nothing names what the number means. Constants declared with final val are excluded, as are the round scale factors 100, 1000, 10000, 100000, 1000000 and 1024.

A bare number carries no unit and no reason. A reader meeting 86400 has to work out that it is a day in seconds, and cannot tell whether the 86400 three files away is the same quantity or a coincidence - so when the value has to change, some occurrences get updated and others do not. Naming it once turns that guesswork into a definition and makes every use consistent by construction.

The following code illustrates the pattern detected by this rule:

Extract the literal into a named constant whose name states the quantity and its unit, for example final val SecondsPerDay = 86400, and use the name at each site. Where the value is a duration or a size, prefer a typed representation - scala.concurrent.duration.DurationInt gives 1.day, which carries the unit in the type.

This detector does not need any configuration.