clos initforms

Thread View: comp.lang.clos

4 messages

[T] Back to Threads [V] Tree View [G] Group Articles

4 total messages Started by Jeffrey B Kane Mon, 09 Nov 1992 05:35

#280

Author: Jeffrey B Kane
Date: Mon, 09 Nov 1992 05:35

48 lines
1907 bytes

I was wondering if someone could suggest the best solution
for the following problem: 

I have a class with several slots As an example:

(defclass test-class ()
	((slot-1	:initarg :slot-1
		:initform 1
		:accessor slot-1)
	(slot-2	:initarg :slot-2
		:initform ?????      ; <- The question
		:accessor slot-2)))

The problem is that I need for slot-2 to default to the same value as
slot-1 if the user does not specify it in the constructor.

(setf my-class-1 (make-instance 'test-class :slot-1 12))

(setf my-class-2 (make-instance 'test-class :slot-1 12 :slot-2 18))

what I want is a generic way to have slot-2 = slot-1 in the first case and
slot-2 = 18 (the supplied value) in the second.  I'm looking for a general
enough solution so I don't have to do something like:

(defclass test-class ()
	((slot-1	:initarg :slot-1
		:accessor slot-1)
	(slot-2	:initarg :slot-2
		:accessor slot-2)))

(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

===============
Jeffrey Kane, MD
Kane Biomedical Systems
Boston MA

clos initforms

#282

Author: Eric Peterson x7644
Date: Mon, 09 Nov 1992 15:49

39 lines
1855 bytes

   Jeffrey> (defclass test-class ()
   Jeffrey> 	((slot-1	:initarg :slot-1
   Jeffrey> 		:initform 1
   Jeffrey> 		:accessor slot-1)
   Jeffrey> 	(slot-2	:initarg :slot-2
   Jeffrey> 		:initform ?????      ; <- The question
   Jeffrey> 		:accessor slot-2)))

   Jeffrey> The problem is that I need for slot-2 to default to the same value as
   Jeffrey> slot-1 if the user does not specify it in the constructor.


I believe the following will do what you want provided that you are
willing to call with :slot-2 first when both initargs are used (see
CLtL2 28.1.9.4. first paragraph after the last bullet):

(defclass test-class ()
  ((slot-1 :initarg :slot-1
           :initform 1
           :accessor slot-1)
   (slot-2 :initarg :slot-1 :initarg :slot-2 
           :accessor slot-2)))


Required call order for non-defaulting case:

(make-instance 'test-clas :slot-2 5 :slot-1 3 )


I hope this helps.

                                   Eric Peterson (speaking for myself)
                                   Systems Research and Applications
                                   2000 15th Street North
                                   Arlington, VA 22201
                                   USA
                                   peterson@sra.com
                                   (703) 558-7644
                                   Fax:  (703) 558-4723

Re: clos initforms

#283

Author: Jose E. Hernandez
Date: Mon, 09 Nov 1992 16:43

39 lines
1650 bytes

|> I have a class with several slots As an example:
|> 
|> (defclass test-class ()
|> 	((slot-1	:initarg :slot-1
|> 		:initform 1
|> 		:accessor slot-1)
|> 	(slot-2	:initarg :slot-2
|> 		:initform ?????      ; <- The question
|> 		:accessor slot-2)))
|> 
|> The problem is that I need for slot-2 to default to the same value as
|> slot-1 if the user does not specify it in the constructor.
|> 
|> (setf my-class-1 (make-instance 'test-class :slot-1 12))
|> 
|> (setf my-class-2 (make-instance 'test-class :slot-1 12 :slot-2 18))
|> 
|> Jeffrey Kane, MD
|> Kane Biomedical Systems
|> Boston MA

(defparameter *default-test-class-slot-value* 1)

(defclass test-class ()
	((slot-1 :initarg :slot-1
	 	 :initform *default-test-class-slot-value*
	 	 :accessor slot-1)
	 (slot-2 :initarg :slot-2
		 :initform *default-test-class-slot-value*
		 :accessor slot-2)))

(defmethod shared-initialize ((inst test-class) slots &rest initargs
                              &key slot-1 slot-2)
   (if (and slot-1 (not slot-2))
      (apply #'call-next-method inst slots :slot-2 slot-1 initargs)
    (call-next-method)))

jeh

Re: clos initforms

#291

Author: Russell G. Almond
Date: Tue, 10 Nov 1992 20:15

39 lines
1738 bytes

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.		
1700 Westlake Ave., N Suite 500		
Seattle, WA  98109			
(206) 283-8802				
almond@statsci.com

Thread Navigation

This is a paginated view of messages in the thread with full content displayed inline.

Messages are displayed in chronological order, with the original post highlighted in green.

Use pagination controls to navigate through all messages in large threads.

Back to All Threads