Placeholder

PWI chapter

Class Design

Internal by default, behavior-only classes against state-only types, the two sanctioned uses of interfaces, and closing concrete descendants.

The guidance is language-independent. Implementations differ where the underlying library differs; the concept does not.

C#
Internal by default, behavior-only classes against state-only types, the two sanctioned uses of interfaces, and closing concrete descendants.
Python
Two kinds of class and why that separation holds, no inheritance for extension, and naming conventions for polymorphic types.