[5.0] trying to auto init a nil field on first ref...

[Ando Sonenblick <ando@...>]

Gang,

I have a table that represents a rectangle.  Normally it'd be set up 
like:

r = {
   top = 0
   left = 0
   right = 100
   bottom = 100
}

so that if I then:

r.top = r.top + 10
print(r.top)

I get "10"

What I'd like to do however is have the four fields, if nil when 
referenced, auto default to zero.  I've been trying to get this with 
__index and __newindex in a metatable, but I can't seem to find a way.

In other words, say I do this:

r = {}
r.top = r.top + 10
print(r.top)

I want want lua to successfully realize that r.top is nil and instead 
of throwing an error, auto init r.top to zero, add 10 to it, and then 
print the result

Is this possible?  I'm staring to confuse myself now more than gain any 
clarity....

Thx mucho,
Ando

-----------------------
Ando Sonenblick
SpriTec Software
www.spritec.com