Some people complain that inheritance is hierarchical (which is what most object-oriented languages provide). They would also like to see more operations available (set operations are quite common in specialized systems). The former is a kind of language dependent feature commonly found in object- oriented languages which are then associated with the term "inheritance" (although they don't need to be. For example, delegation languages allow graph inheritance stuctures). Some don't like the coupling of classes (as in Jade), but in the author's opinion many of their complaints are easily answered. In systems that provide inheritance, inheritance provides a simple and elegant way to reuse code and to model the real world in a meaningful way.
Others complain multiple inheritance is too complicated because it brings up the issues of shared bases and member conflict resolution. But most modern systems support Multiple Inheritance by employing semantic resolution strategies or renaming, and most consider MI to be highly desirable. See the latter part of section 1.9 for an example of why MI is important.
Some prefer association to MI, claiming "roles" (as defined in [Rumbaugh 91]) should be associations and inheritance should be reserved for a single hierarchy "creation" mechanism, however this loses polymorphism and loses the use of inheritance for typical classification. Representation "roles" can be supported by dynamic multiple inheritance (DMI) in many situations.
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