Primitives

Wrap every primitive that carries domain meaning in a dedicated type. Let the compiler enforce what your variable names only suggest.

Article: Primitives

In 1999 NASA lost a $327 million orbiter to a float: one team measured in pound-force seconds, another in newton seconds, and the type system had nothing to say. Your bug will be smaller and the mechanism identical: a raw value that meant one thing was used where a raw value meaning another was expected, and nothing caught it.

Four rules push the domain into the type system: two parameters of the same primitive type, a field whose name promises more than its type, a String that is really an enum, and a validating constructor with a back door.