On 07.09.2009, at 21:29, Eliot Miranda wrote:

> On Mon, Sep 7, 2009 at 12:19 PM, Bert  
> Freudenberg<bert at freudenbergs.de> wrote:
>> On 07.09.2009, at 20:56, Eliot Miranda wrote:
>>>
>>> I have fixes for this integrated in Qwaq.  This is work I did for
>>> VisualWorks a while back.  The idea is to add a set of mirror
>>> primitives, so called because they do reflection, to ContextPart.
>>> These primitives implement the basic operations of the object model
>>> needed for execution simulation, fetching an object's class,  
>>> accessing
>>> its named and indexed instance variables, and the number of indexed
>>> instance variables, sending a message, but they take the object
>>> operated on as a parameter and so do function without sending  
>>> messages
>>> to that object.
>>
>> Wouldn't that break encapsulation in a way we never had to before?
>
> If one dared use those primitives for anything other than simulating
> the VM then I suppose they're a little worse than instVarAt:put: and
> basicAt:put:, but not so much.

These are fundamentally different. #instVarAt:put: and basicAt:put:  
are regular methods that an object itself implements to give others  
access to its internal state. It can very well chose not to.

>  I think it is much more dangerous to
> have a debugger that appears to be correct but breaks one's code in
> ways that are horribly difficult to understand.
>
> Note that both Self and Newspeak (and VisualWorks) take the mirror
> primitive approach.  But there is certainly a security issue and one
> wants to medate access to the mirror primitives carefully.


Alas we have no way for restricting access in Squeak.

Anyway, these primitives are useful for debugging indeed. How about  
disabling them in production mode?

- Bert -