Object references. Most object-oriented languages support object references. It is
rarely considered a modeling feature, but mainly a mechanism for representing the state
of objects. In Smalltalk it is the only way to represent the state of an object and this
state is considered a private part of the object. In Reference [BC87] the representation
of part objects in Smalltalk has been considered, and an extension of Smalltalk was
proposed.
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Part patterns. Nesting of procedures is supported by most Algol like languages,
including Pascal, but rarely in object-oriented languages. Nesting of classes is only
fully supported by Simula and BETA. C++ allows nesting of classes, but within a
nested class it is not possible to refer to names in the enclosing class. Nesting of classes
in C++, is thus a pure scope mechanism.
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