Re: Globals vs. Locals

[Uli Kusterer <witness.of.teachtext@...>]

On Aug 5, 2005, at 21:32:06, Roberto Ierusalimschy wrote:
> I did not say there was automatic globals. What I meant was this: When
> you see a function like
>
>   int foo () { a = 1; }
>
> in C, C++, C#, Pascal, Objective Pascal, Ada, Java, Scheme, Lisp  
> (and a
> lot of other languages), do you think that "a" is local to the  
> function?
> Or does it look more like a global (that is, external to the  
> function)?

Roberto,

 being a C programmer, in the above function I'd expect it to be  
global, because a local variable would be declared somewhere. But  
that's because I have grown used to the way C does things. If this  
was C++ or TADS, I'd only expect it to be declared in an outside  
scope, i.e. as a global or an instance variable. If this was PHP, I'd  
expect this to be local (And pretty pointless at that).

 As a human, I'd expect a to be in some outside scope *in this  
particular example* simply because it would be pretty pointless  
otherwise to put 1 into a variable (*and* not return anything) and  
then forget about it. But the Lua compiler can't think like a human,  
because a function that caches a value could look very different yet  
still require a global:

int cachedFoo()
{
    if( foo == nil )
        calculateFoo();
    return foo;
}

 There is no right answer to this. It's simply a matter of who you  
expect to be the users of your app and the scripting language  
embedded in it.

Cheers,
-- M. Uli Kusterer
http://www.zathras.de