RE: proposal (RE: Making vars local by default)

["Samson, Lyndon [IT]" <lyndon.samson@...>]

All this bru-ha-ha is because of implicit scoping, why not just have the
global
keyword introducted and do like visual basic with option Explicit?


-----Original Message-----
From: Tom _ [mailto:tom7ca@yahoo.com]
Sent: Friday, June 01, 2001 7:05 AM
To: Multiple recipients of list
Subject: Re: proposal (RE: Making vars local by default)


> >Nobody who doesn't want to would have to switch to 
> >using ":=".  Code that uses "=" would continue to
> >work and seamlessly work with code that uses ":=".
> >"x := y" would simply be a shorthand for "put
> >'local x' at the beginning of the function and
> >write 'x = y'".
> 
> That's not the whole picture: from then on both
> coding styles would start
> to proliferate and gradually become part of libs,
> tools, etc... :(

What I proposed allows the two styles to co-exist
and interoperate.  That removes the objection that
such a change would break existing code.

Whether you want to allow the two styles to co-exist
indefinitely is a policy choice.  Personally, I'd
prefer to see the current style become obsolete
in a release or two, but I see the two styles 
co-existing as much less of a problem than just having
the current default, which I view as very dangerous.

> Assignment is not really the issue, let's please not
> overload that (quite standard) concept.

Yes, the issue is scoping.  Having multiple
assignment operators for different scopes is
one well established approach to the problem
(cf. the "R" language).

> I really don't see what the big deal 
> with globals is.

Scoping is a big deal because scoping
bugs are subtle and often show up out of nowhere
long after they were introduced.  Lua is one
in a long, long line of languages that were
initially designed with convenient but
dangerous scoping rules; fixing something like
that is always painful, but it beats the
alternatives.  Just think of the evolution of 
scoping in languages like Lisp and Perl.

> Have you considered the following:
> 
>     function blah(...)
>         local v = {}
>         ...
>         v.a = ...
>         ... = v.b
>         ...
>     end
> 
> Would that, plus "test/undefined.lua" perhaps, (at
> least partially) address your concerns?

Not only is that style expensive, it also clearly
makes a safe programming style second class and 
therefore discourages its adoption by other authors
of Lua code and libraries.

Tom.


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