Re: Next Version of Lua?

[James Snyder <jbsnyder@...>]

On Jun 10, 2009, at 5:24 AM, Luiz Henrique de Figueiredo wrote:
> > * VM: Add support for __overrideindex (as the meta-method's name
> > suggest, override a key in the table which already contains a non-nil
> > value with a new value, nil or otherwise)
>
> The usual answer is to use proxies.


Proxies work well for a fair number of things, except for some types  
of lazy evaluation like accessing tables in a remote Lua environment.   
If one wants to do things like call functions in the remote  
environment, but also be able to index values on remote tables and  
have them be able to be accessed locally, it is difficult to decide  
when a series of __index events should result in returning another  
proxy vs returning the value on the table.

Say for example you have a handle for the remote environment,  
conveniently called "handle":

handle.foo.bar(a,b,c)

It's pretty easy to know how to deal with this situation since it  
includes a call, but what if that same remote table called foo has a  
value on it that I want:

local_value = handle.foo

Do I make local_value a proxy or the actual value?  The metatable  
hooks allow for dealing with a number of operations, but what if I  
just want to do somehting like:

math.cos(local_value)

It would be nice to be able to hook things maybe at the index2adr  
level, or provide some way so that when the actual type is checked or  
looked up that the value could be pulled down just before the operation.

Some of this functionality could come from adding a __tonumber, and  
covering a few more type conversions, but this would provide a more  
general lazy evaluation hook.

I assume it would also potentially slow down every lookup for data,  
but perhaps there's some way to make that hit negligible?

--
James Snyder
Biomedical Engineering
Northwestern University
jbsnyder@fanplastic.org
http://fanplastic.org/key.txt
ph: (847) 448-0386

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