Re: Lua5.0 new "For" question

[Eero Pajarre <epajarre@...>]

> Hmmm... so, If I understand correctly, the closure 
> is "frozen" or "closed" once the local x is out of scope.
> I find this one also interesting:
>
>
> function fie()                                 
>       local x=789
>       f = function() return x end --global f
>       print(f()); 
>       x=123; 
>       print(f());
> end
>
> fie() -- will print 789 newline 123
>
> Apparently, you can still change the contents of 
> the closure's x whilst the local x is in scope,
> because they are the same x. Which makes sense 
> due to the lexical scoping.

You can change it even later ;-)
Try:

function fie()
  local x=123;
  function f() return x end
  function g(y) x=y end
end

fie();

print(f()); --prints 123
g(321);
print(f()); --prints 321


This is powerfull stuff....
(Were upvalues read-only?)

Btw. I became curious about what Peter had suggested
year ago. I think that what he wanted (protected datatypes
in Lua) might be implementable with closures. Create an object
which has its internals in a closure, which can only be
accessed by the interface functions, hmmm, I don't know if there
are any holes here.



		Eero