Re: A question about 'next'

[Asko Kauppi <askok@...>]

I had a similar need lately, making "fingerprints" for table contents.

Did it by collecting the field fingerprints into a table, then sorting  
the table, then concatenating. Sorting guarantees iteration order did  
not matter.

Example:
	"x=1", "y=2"	-> sorted, concat	->	"{ x=1, y=2 }"
	"x=3", "y=4"	-> sorted, concat	->	"{ x=3, y=4 }"
...
	"{ a={x=1,y=2}, b={x=3,y=4} }"

Such a string was used as a cache key in luaSub constraints management.

-asko


Enrico Colombini kirjoitti 23.2.2008 kello 17:04:

> I'm aware that, when using 'next', "The order in which the indices  
> are enumerated is not specified".
>
> But my question is:
> - Is that order always the same, given the following conditions?
>
> t = {
>  a = { x=1, y=2 },
>  b = { x=3, y=4 }
> }
>
> for k,v in next, t do
>  -- don't change k (of course)
>  -- don't change v
>  -- may change v.x, v.y
>  -- may add new fields to v
> end
>
> Given those assumptions, is the order of traversal of t always the  
> same in different invocations of this loop (either b,a or a,b in  
> this case) or is this not guaranteed?
>
>  Enrico