Microsoft Word OpenIssuesInOO. doc

4.1.3.  Support for composition in other languages 

Composition is to some degree supported in object-oriented languages 

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Part objects. C++ and Eiffel [Mey88] support part objects. In C++ a class attribute 

may be a instance of another class. In Eiffel it is a property of the class whether or not 

an instance of it is a part object. This means that all instances of a class are either part 

objects or referenced from other objects. They cannot be both. 

 

In BETA a part object may be an instance of any class and a part object may also be 

referenced from other objects. 

 

In BETA a part object may also bind virtual patterns

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 in the object being instantiated 

and operations in the part object may thus have an effect upon the enclosing object. 

This is possible by combining a part object with block structure and singular objects. 

This feature is a useful alternative to multiple inheritance, which is further discussed in 

section 4.2. 

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