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Diffstat (limited to 'txr.1')
| -rw-r--r-- | txr.1 | 42 |
1 files changed, 42 insertions, 0 deletions
@@ -23411,6 +23411,48 @@ Only instance slots participate in the duplication. Since the original structure and copy are of the same structure type, they already share static slots. +This is a low-level, "shallow" copying mechanism. If an object design +calls for a higher level cloning mechanism with deep copying or other +additional semantics, one can be built on top of +.codn copy-struct . +For instance, a structure can have a +.code copy +method similar to the following: + +.cblk + (:method copy (me) + (let ((my-copy (copy-struct me))) + ;; inform the copy that it has been created + ;; by invoking its copied method. + my-copy.(copied) + my-copy)) +.cble + +since this logic is generic, it can be placed in a base +method. The +.code copied +method which it calls is the means by which the new object is notified that it +is a copy. This method takes on whatever special responsibilities are required +when a copy is produced, such as registering the object in various necessary +associations, or performing a deeper copy of some of the objects held +in the slots. + +The +.code copied +handler can be implemented at multiple levels of an inheritance hierarchy. The +initial call to +.code copied +from +.code copy +will call the most derived override of that method. + +A derived method can use the +.code call-super-method +to call the corresponding method in the base class. + +Thus derived structs can inherit the copy handling logic from base structs, and +extend it with their own. + .coNP Accessor @ slot .synb .mets (slot < struct-obj << slot-name ) |