🚀 go-pugleaf

Jeffery Asks:

> (defun make-test-class ((me test-class) &key (:slot-1 1) (:slot-2 nil))
> 	(unless slot-2
> 		(setf slot-2 slot1)) ; if no default value for slot-2 use 
>                                    ; slot-1's value
> 	(make-instance 'test-class :slot-1 slot-1 :slot-2 slot2))

> The problem I see with this approach is that it does not let you specify a nil 
> value for
> slot-2.  What I'm looking for is a general solution that doesn't lock out some 
> previously
> defined "bad" value (nil in the above example).

>     Jeffrey


I think you want the third (suppliedp) argument for &key (and &optional)
parameters in a lambda list.  Thus:

(defun make-test-class ((me test-class) &key (:slot-1 1)
                                             (:slot-2 nil slot-2?))
	(unless slot-2?
		(setf slot-2 slot1)) ; if no default value for slot-2 use 
				     ; slot-1's value
	(make-instance 'test-class :slot-1 slot-1 :slot-2 slot2))

This should do what you want.  (There should be an equivalent way to to
it with a shared-initalize method, I'm not as familiar with that
approach.)


			Russell Almond			   
Statistical Sciences, Inc.		
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