4.3. Deviations from ANSI CL standard
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## 4.3. Deviations from [ANSI CL standard]

`DEFCLASS` supports the option `:METACLASS` `STRUCTURE-CLASS`. This option is necessary in order to define a subclass of a `DEFSTRUCT`-defined structure type using `DEFCLASS` instead of `DEFSTRUCT`.

When `CALL-NEXT-METHOD` is called with arguments, the rule that the ordered set of applicable methods must be the same as for the original arguments is enforced by the implementation only in interpreted code.

`CLOS:GENERIC-FLET` and `CLOS:GENERIC-LABELS` are implemented as macros, not as special operators (as permitted by [sec_3-1-2-1-2-2]). They are not imported into the packages “COMMON-LISP-USER” and “COMMON-LISP” because of the [ANSI CL standard] issue GENERIC-FLET-POORLY-DESIGNED:DELETE.

`PRINT-OBJECT` is only called on objects of type `STANDARD-OBJECT` and `STRUCTURE-OBJECT`. It is not called on other objects, like `CONS`es and `NUMBER`s, due to the performance concerns.

| These notes document CLISP version 2.45 | Last modified: 2008-05-14

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