Re: TypeDesc/__getAllegedType replacement notes

On Oct 16, 2007 6:36 PM, Kevin Reid <[email protected]> wrote:
> I'm working on trying out the "replace TypeDesc with ObjectExpr
> +scope" idea, and here are my notes and problems so far. Please
> provide design opinions.
>
> * There is still a kind of object which __getAllegedType returns,
> which might or might not also be a guard. I've been calling them
> "signature" just to have a word to distinguish them from old TypeDesc
> code.
>
> * What is the protocol of a "signature" object? What I have now is {
>     to getNode()
>     to getEnvironment()
>   }

Seems good.


> * Nice simplification: The equivalent of e.g. a MessageDesc is just a
> "signature" with an EMethod node instead of an ObjectExpr node.

I like it.


> * TypeDesc has a "supers" field, which is used in interface
> expressions. What should correspond to this in the new world? My
> answer for the moment is that it's an additional field in the
> "signature" object. Another possiblity would be using a NKObjectExpr
> (nonkernel) which has "extends" in the syntax, but that seems not
> quite right since the alleged-type is defined in terms of the kernel.

I'm not sure I understand the first option. What would be the value of
a signature's getSuper() (or whatever the name of the new field is)?


> * Currently, if an object "extends" another, the latter's alleged
> messages are included in the former's __getAllegedType answer. How
> should this be handled? Following the plan we made suggests that all
> the match expressions should be included in the alleged type, but if
> "super"s are to be included then including the delegating matcher is
> pointless and misleading; but without revealing inside-the-braces
> information I see no way to hide the relevant matcher.

 If we come up with a satisfying answer for the previous question --
what's a signature's getSuper()? -- might that take case of this as
well?

For example, when an object is asked __getAllegedType(), it asks its
matcher for their __getAllegedType() as now, and includes the answer
as the getSuper() value of the signature it makes and returns. Does
this make sense?

-- 
Text by me above is hereby placed in the public domain

    Cheers,
    --MarkM