Appendix C The CLIM-SYS Package

C.4 Multiple-Value Setf

CLIM provides a facility, sometimes referred to as setf*, that allows setf to be used on "places" that name multiple values. For example, output-record-position returns the position of an output record as two values that correspond to the x and y coordinates. In order to change the position of an output record, the programmer would like to invoke (setf output-record-position). However, setf only takes a single value with which to modify the specified place. The setf* facility provides a "multiple-value" version of setf that allows an expression that returns multiple values to be used to update the specified place.

defgeneric* [Macro]

name lambda-list&body options
Defines a setf* generic function named name. The last argument in lambda-list is intended to be class specialized, just as normal setf generic functions are. options are as for defgeneric.

defmethod* [Macro]
name (method-qualifier* specialized-lambda-list&body body)
Defines a setf* method for the generic function name. The last argument in specialized-lambda-list is intended to be class specialized, just as normal setf methods are. (method-qualifier)* and body are as for defgeneric. For example, output-record-position and its setf* method for a class called sample-output-record might be defined as follows:

        (defgeneric output-record-position (record) 
          (declare (values x y))) 
        (defgeneric* (setf output-record-position) (x y record))
        (defmethod output-record-position ((record sample-output-record))
          (with-slots (x y) 
                      (values x y))) 
        (defmethod* (setf output-record-position) 
          (nx ny (record sample-output-record)) 
          (with-slots (x y) 
                      (setf x nx 
                            y ny)))
The position of such an output record could then be changed as follows:

        (setf (output-record-position record) (values nx ny)) 
        (setf (output-record-position record1)  
              (output-record-position record2)) 

CLIM 2.0 User's Guide - OCT 1998

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