TBF that's pretty directly inherited from the Smalltalk ancestry: just like Smalltalk, Ruby simply doesn't have public (data) fields. Although it does provide shortcuts for automatically generating accessors which I don't think Smalltalk did / does.

Funnily enough, Self opted for the opposite tack of not having private data fields (although it does have readonly and read/write slots), but you can trivially swap "data" slots and "method" slots: http://handbook.selflanguage.org/2017.1/langref.html#constru...