Dr Darren of Webel IT Australia makes the case for better object-orientation for Mathematica using pseudo class ADTs without losing the super-functional power of the Wolfram Language Gallery Tutorial Mathematica: POLICY NOTES for the Webel Abstract Data Type (ADT) pseudo classes with inheritance for the Wolfram Language Section
Mathematica: Webel ADT pseudo classes: TIP: Prefer the Decorator Pattern over multiple inheritance of ADT-Method UpValues! (But not because "inheritance is evil" per se, it isn't.) The base ADT libraries make heavy (and very useful) use in inheritance.
Mathematica: Webel ADT pseudo classes: POLICY: Multiple inheritance is supported via ONE (only) ADT-Class and one or more ADT-MemberInterfaces (which have no ADT-Method UpValues)
Mathematica: Webel ADT pseudo classes: ADTs that define membership of ADT-classes in a domain package have ADT-signature MemberInterface[$$:None] and MUST NOT populate ADT-method UpValues in their definers.
Mathematica: POLICY NOTES for the Webel Abstract Data Type (ADT) pseudo classes with inheritance for the Wolfram Language Jump to first slide Dr Darren of Webel IT Australia makes the case for better object-orientation for Mathematica using pseudo class ADTs without losing the super-functional power of the Wolfram Language Sections