型构兼容的继承及其语义

SIGNATURE-COMPATIBLE INHERITANCE AND ITS SEMANTICS

本文揭示了在面向对象程序设计语言中，若允许子类重定义其继承的父类方法以改变这些方法的规约，并且采用类似于Ｓｍａｌｌｔａｌｋ－８０中的继承机制的语义，将导致封装与继承之间的一个新问题．为此，本文提出了一种新的继承机制─—型构兼容的继承，以代替传统的增量继承．型构兼容的继承是一种灵活的代码复用机制，并且能够充分支持封装．本文给出了型构兼容的继承的操作语义和指称语义，为其在面向对象程序设计语言中的实现奠定了基础．

In this paper, the encapsulation issue in object-oriented languages is raised that adopting the semantics of inheritance such as the 'method lockup' algorithm in Smalltalk-80 and allowing subclasses to redefine inherited methods tochange their specifications severely compromises encapsulation in an object-oriented language. To resolve this encapsulation issue, a new inheritance mechanism called signature-compatible inheritance is presented. Signature-compatible inheritance is aflexible mechanism for reusing code and provides sufficient support for encapsulation. For its implementation in object-oriented languages, its operational semantics and denotational semantics are given.