Microsoft Word OpenIssuesInOO. doc

Pattern references. References to patterns has little support in most object-oriented 

languages. References to procedure patterns resemble procedure variables that may be 

assigned procedures as values. If a procedure value includes the static environment 

(object) of the procedure then it is a closure, but if it only includes a pointer to the code 

it is not. The function pointer in C is an example of procedure variables, but since C 

does not have bock structure there is no issue of a procedure value being a closure. C++ 

supports closures via pointers to member functions. Algol 60 supports closures via its 

formal procedure parameter mechanisms, and Lisp-like languages including Scheme 

[RC86] and CLOS [Kee89], have direct support for closures as first class values. 

Smalltalk and Self [US87] have closures in the form of blocks. A Self block can, 

however, not be invoked after its enclosing method has returned. In  Smalltalk and Self 

it is not possible  to pass a reference to a method as a closure. In Self it is, however, 

possible to obtain the same effect by using reflection. 

                                                 

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A virtual procedure pattern is similar to a virtual function in C++. Virtual patterns are further discussed 

in section 4.3. 

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References to classes are even more rare and are not supported by any of the 

mainstream statically-typed languages such as C++ and Eiffel. In Smalltalk classes are 

objects and in Self objects are used instead of classes. I.e. references to classes (in Self 

objects used as classes) are directly supported by the language.