Understanding Dart Class Modifiers by Using Lattices

The fact that Dart’s class modifiers form a clean lattice means the design is internally consistent. There are no arbitrary restrictions or special cases.

The lattice gives me the opposite impression —

• There are 'arbitrary' restrictions about 'impossible' cases. You need to memorize the rule that "mixinable classes must be extendable".
• There are non-transitive edges with respect to certain properties (possible < impossible < possible). Ideally, the lattice structure would be preserved when mapped through various properties of interest.
• The lattice structure doesn't follow the keyword structure, so you have to first decode the keywords to understand the properties, then consider the properties in the lattice.

There's discussion on this article on /r/dartlang which may be of interest, including perspectives from @munificent from the Dart team.