> Because primitives are meaningless. That depends on your problem domain. If I'm implementing a library of data structures and algorithms (which I have to do,

> Because primitives are meaningless. That depends on your problem domain. If I'm implementing a library of data structures and algorithms (which I have to do, because most standard libraries are subpar on this front), then I definitely want to work with raw integers or sequences (but probably not strings - they should be just a special case of sequences). > "Message" does. "Contact person" does and has conceptually nothing in common with a "Message". No disagreement in this particular case. It's indeed best to have separate types for things on which different operations make sense. But, personally, I find it more tasteful to have little to no algorithmic logic at the level of business domain entities. Algorithms work on mathematically structured data.