[armedbear-devel] SETF for JFEILDS

[logicmoo at gmail.com]

----- Original Message ----- 
From: "Alessio Stalla" <alessiostalla at gmail.com>
To: <dmiles at users.sourceforge.net>
Cc: "Armed Bear" <armedbear-devel at common-lisp.net>
Sent: Monday, November 23, 2009 5:42 AM
Subject: Re: [armedbear-devel] SETF for JFEILDS


On Mon, Nov 23, 2009 at 2:36 PM,  <logicmoo at gmail.com> wrote:
>> Does anyone object to adding this to java.lisp? If not could it be done?
>>
>> (defun (setf jfield)
>> (newvalue class-ref-or-field field-or-instance &optional ( instance :noinst) (value :novalue))
>> (if (eq instance :noinst)
>> (jfield class-ref-or-field field-or-instance newvalue)
>> (jfield class-ref-or-field field-or-instance instance newvalue)))

>It seems a nice idea to me, but there are a couple of things that I
>don't understand:

A>- why :noinst and not simply nil?

JFIELD is defined as:   class-ref-or-field field-or-instance &optional instance value
The valid argument patterns for this operation are: 
  (class-ref  field-name): to retrieve the value of a static field. 
  (class-ref  field-name  instance-ref): to retrieve the value of a class field of the instance. 
  (class-ref  field-name  primitive-value:) to store primitive-value in a static field. 
  (class-ref  field-name  instance-ref  value): to store value in a class field of the instance. 
  (class-ref  field-name  nil  value): to store value in a static field (when value may be confused with an instance-ref). 
  (field-name  instance): to retrieve the value of a field of the instance. The class is derived from the instance. 
  (field-name  instance  value): to store value in a field of the instance. The class is derived from the instance. 

JFIELD doesn't distingusih between static and non static fields

Also cases of  "class-ref  field-name  instance-ref  value"  (accessing  superclass field)

Depending on how the field is defined

  (setf (jfield  *MyClass* "someStaticBooleanField") NIL)
      it is distinguable from   
  (setf (jfield  *MySuperClass* "nonStaticBooleanField" *my-instance* ) NIL)


--------------------------------------------------------------------------------------------------------------------------
A>- value is not used, what's the point of it?  

correct the  "default :novalue" is not needed.    
(I was debugging and trying to find corner cases with all those bizzare legal jfield signatures )


   but... "value" as an &optional was needed to match the signature of what is legal for jfield so things like this can work:

 (define-symbol-macro %iscold (jfield "org.armedbear.lisp.Lisp" "cold"))
    %iscold ;; ==> NIL    
    (setq %iscold T) ;; ==> T    
    %iscold ;; ==> T     
    (setq %iscold NIL) ;; ==> NIL