This is a good account of a software modelling process. But, this is not specific to booleans. Database constraints involve the same issue. One motivation for e

This is a good account of a software modelling process. But, this is not specific to booleans. Database constraints involve the same issue. One motivation for encapsulation in software was to preserve constraints in the data (or in other words, disallow improper states). Encapsulation allows only internal functions to manipulate the data, and the developer just needs to checks that these functions are doing it correctly. Or, as pointed out in the post where multiple booleans are merged into a single enum, encode the constraints into the data itself ie. use the constraints of the host programming language. But this wont be possible in general - for instance if your language doesn't have sets/dictionaries, how would you encode uniqueness of values directly using arrays and lists? It would have to be done using interface functions.