Subj : Re: String property & DOM synchro
To   : netscape.public.mozilla.jseng
From : Brendan Eich
Date : Tue Jun 29 2004 09:36 am

Lorenzo Pastrana wrote:

>     case STR:
>         // This works for simple Get/Set but on
>         // obj.strprop.concat(otherstr); it fails to update the DOM
>         return STRING_TO_JSVAL(
>             jsNewString(jscontext,
>              (char*)((str&)_data).Export(),
>              ((str&)_data).GetLength()));


I'm assuming Export makes a copy?  Might want to check for null if 
out-of-memory is possible on your OS.


>>You may be misusing the JS_NewString API.
> 
> 
> It might be, but anyway this is not a memory management problem really :
> 
>     - I want to rely on SM's JSString 'sandard' implementation in JS space
>     - I dont own JSString code and I'm not inclined to branch


Good, and good -- I wouldn't have it any other way ;-).


>     - My DOM engine is accessed by messages, so the buffer I provide to
>         JS_NewString is allready a copy.


Right, Export() above.


>     - The string implementation I'm using in the background does not want
>         to 'share' it's buffer (usual encapsulation/ownership problem)..


That means you have to copy, but it doesn't say anything about 
synchronizing string values between the two string-spaces.


>     - Since the new JSString works on a copy of the data, it needs to be
>         re-synched into the DOM after modifications


It's not the string (JSString) that needs to be changed (JSStrings 
should not in general be modified -- there could be several references 
to one, and you can't edit the chars stored in it safely unless you know 
you have the only reference).

Rather, the property is what gets modified.  So why can't your 
generic_setter handle that?


>     - At this point I'm missing some notification mechanism called by
>         JSString or whatever other solution :-/


You have the wrong level of data structure.  A string is a value, like 
3.14 or true.  There's no reference type (pay no attention to the C 
pointer behind the curtain! :-), no notification for changes to the 
immutable value (the Unicode character sequence), and indeed no mutation 
methods explicitly provided for JSString.  The value container that can 
be mutated, and that does have well-defined notification APIs, is the 
object property.

So you want JSClass.setProperty or a per-property setter.

/be

.