Re: Lua5.0 new "For" question

[Eero Pajarre <epajarre@...>]

Peter Hill wrote:
> Eero Pajarre:
>
> > Btw. I became curious about what Peter had suggested year ago. I think
> > that what he wanted (protected datatypes in Lua)...
>
>
> Do you mean the idea of making true Abstract Types by hiding the
> internals with some sort of locked tags as a key? Ie:

I was mostly thinking along the lines of the code provided by Björn,
using closures for data hiding.

> If so, you've got a good memory! I didn't think at the time that anybody
> even noticed the suggestion.

(No, I cheated and checked the archives on www.lua-users.org)

> I'm having trouble trying to imagine a way to get the same functionality
> (which doesn't mean it can't be done of course!). As an example, let's try
> to implement complex numbers as an abstract type. With the tag-key method we
> have:

Thinking of, it I see problems with the implementation, although some sort
of encapsulation can be achieved. I will have to consider this more...

> What did people generally use (a) upvalues and (b) tag methods for?
>
> What were the forces / desires that have generated the new (a) setglobals
> (b) lexical scope and (c) metatables... and how well are they achieving
> those goals?

I am still new to more advanced Lua features. I am currently
using setglobals for catching programming errors, (For example
by disabling accidental creation of new global variables), I think
I might use it also for creating a "sandbox" for untrusted code.

I am not yet actively using lexical scoping, but I did not use
upvalues either...

Metatables I use both in my glue code to C/C++ stuff and also
for doing "object oriented Lua" (classes, stating on inheritance)
(I think these were the two typical uses for tags also)


		Eero