simple object model

[Jecel Assumpcao Jr]

On Monday 02 April 2001 17:05, Steve Dekorte wrote:

> > Jecel Assumpcao Jr wrote:
> >   1) base level: objects look like menus, morphs, strings, etc...
> >
> >   2) reflective level: objects look like hash tables (or
> > collections of slots)
> >
> >   3) implementation level: you have the actual memory format of
> > objects with tricks such as "maps" to help make cloned objects
> > smaller
> >
> > What I am investigating here is the possibility of bringing levels
> > 2 and 3 closer together (ideally level 2 would be a slightly "sugar
> > coated" version of level 3).
>
> I'm not sure what you mean here.
> If you mean:
>   1) method invocation

Yes.

>   2) reflection

Ok.

>   3) object model

Well, I mean the object model as seen by the implementor.

> Then scripting languages like python and lua unite the first 2:
>
> 1) table.slotName() = call the returned function
>
> 2) a = table.slotName (get slot value, be it a function or data)
>      table.slotName = b (set slot value to data or function)

That is exactly it. But I don't like how this unification made 1 feel 
less object-like than it does in Smalltalk or Self. But it is 
reasonable for people used to C++.

> And Lua brings 3 (the implementation of the object model) up to the
> level of 1&2 (the language itself) by providing "hooks" that let you
> define what happens when a table lookup fails:
>
> function index(table, slotName)
>    local parent = rawgettable(table, "_parent")
>    if parent then return parent[slotName] end
>    error("object "..tostring(table).." has no slot
> named:"..tostring(slotName))
> end
>
> You can likewise define the clone method, so you're free to do things
> like NewtonScript style slot creation on write if you like, to
> conserve memory and instantiating time at the expense of slot lookup
> time.
>
> It doesn't get much more "light-weight" than this.

Well, this is all at what I would call level 2. I still have no idea of 
what a hash table looks like in the computer's memory. I would have to 
look at Lua's C source code to find that out.

-- Jecel