A look at the object oriented language sather
Abstract data types want to make classes be opaque boxes in which the data representation and function implementations are to be hidden. Chapter 2 introduces the basics of class-based programming. CLOS demands the existence of a topological sort of the ancestors the direct and indirect parents that defines the precedence among them for inheritance .
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Hoelzle, C. Instances that already exist must be dynamically altered before methods may be applied. DeMichiel, R. The design of Sather was based on Eiffel but focussed more on expressive power, efficiency and simplicity than on the formal and theoretical issues addressed by Eiffel. CLOS demands the existence of a topological sort of the ancestors the direct and indirect parents that defines the precedence among them for inheritance . Descendents have access to all features and there is a strong link between subtyping and inheritance. If conflict resolution on a single feature basis should become necessary, an inherited feature can be aliased before it is shadowed by a subsequently included class and can later be aliased back to shadow the unwanted one. We do not believe in single language approaches. In a class-based language, a class represents the common structure and behavior of all objects that belong to it. Each feature name is assigned a unique integer value.
Schmidt- Stephen M. Either restricting the specialization of attribute types or forcing the redefinition of all code which makes these assignments would exclude many useful forms of reuse. For a young language the suite of tools is acceptable.
Twast be disjoint or agree in the typing of their features and a feature must oxi in either of them or stem from the same ancestor. The tension between different goals leads to somewhat different notion of types. There are a few formal type systems that combine these views cf. Bobrow: The Art of the Metaobject Protocol. Eiffel 3. In part, this is deliberate because of the wide variety of requirements imposed by different applications. Sather has been in operation since mid and a beta release has been publically available since mid The substitution semantics of parameterized types permits implementations ranging from code sharing to specia. Finally there is a tension between static typing and dynamic dispatch. Gunter, G. Smalltalk was partially based upon Simula67 , but introduced many new features. What is covered by library classes? As we move from one end of the object-orientation spectrum to the other, properties of the languages will change. Imperative, since it is not possible to get by without writing a routine, despite the fact that all ingredients for the child are already there someplace in the respective parents. A full specification is often undesirable since the most trivial properties, like bounds for array indexes and void references for instance, quickly dominate the program text.
In Sather, which stresses implementation inheritance, descendents are not constrained by the semantics of their parents.
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