Subj : Re: custom class definition question
To   : netscape.public.mozilla.jseng
From : Brendan Eich
Date : Tue Jul 20 2004 09:16 am

Brendan Eich wrote:

> But almost always, when defining properties with tinyids, you don't want 
> each object to have its own copy of the property shadowing the prototype 
> property.  That's wasteful of memory without any benefit.  Tinyids exist 
> for fast dispatching in shared class getters and setters, based on 
> prototype properties that don't need to be shadowed (that in fact may 
> want to have JSPROP_SHARED among their attributes, if they are not 
> JSPROP_READONLY).

In case it is not clear, resolve is called for each object along the 
prototype chain, starting from the directly-referenced object, so long 
as the id being accessed is not defined in each object.

So if you have an instance o whose prototype, o.__proto__, is p, and p 
has tinyid-defined properties that you wish to share rather than shadow, 
then you don't want to do anything when resolve is called on o.  Let its 
caller, js_LookupProperty, walk up the prototype chain to p, where it 
will find the tinyid-defined properties.

Only if each instance o that delegates to p needs its own copy of a 
property, perhaps to hold specific attributes, or to have its own slot 
for property value storage (in which case, do not use JSPROP_SHARED), or 
for a custom getter/setter that are specific to that property, do you 
want to define the property in o.

/be

.