Subclassing errors, OOP, and practically checkable rules to prevent them

TL;DR

This paper identifies subclassing errors in OOP that compromise interface separation and introduces a set of practical, mechanically verifiable rules to prevent such errors, challenging traditional OOP principles.

Contribution

It proposes a novel set of checkable rules to prevent subclassing errors, highlighting limitations of OOP and questioning its suitability for reliable software development.

Findings

Rules effectively prevent subclassing errors in examples

The rules are expressive despite being restrictive

OOP may be inherently prone to subtle errors

Abstract

This paper considers an example of Object-Oriented Programming (OOP) leading to subtle errors that break separation of interface and implementations. A comprehensive principle that guards against such errors is undecidable. The paper introduces a set of mechanically verifiable rules that prevent these insidious problems. Although the rules seem restrictive, they are powerful and expressive, as we show on several familiar examples. The rules contradict both the spirit and the letter of the OOP. The present examples as well as available theoretical and experimental results pose a question if OOP is conducive to software development at all.