Re: tables

[Chris <coderight@...>]

On 3/5/06, Dolan, Ryanne Thomas (UMR-Student) <rtdmr6@umr.edu> wrote:

This behaviour is not dangerous; it is expected.  What is dangerous is trying to use the result of the length operator on an array with holes.

In other words, you should never try #{nil, 2} or #{[2] = 2} in the first place.  If you do, you must expect an unpredictable result.

Furthermore, you cannot expect #{nil, 2} to always return 2, nor #{[2] = 2} to return 0.  As I said earlier, the length operator only gaurantees a predictable result with arrays with no holes, so later versions of the interpretter could have #{nil, 2} return 0 and #{[2] = 2} return 2.  According to the definition of the length operator, both 0 and 2 are valid lengths of {nil, 2} and {[2] = 2}.

Can someone define what a "hole" in an array is?  Why can't I have
an array with nil values in it?  The current behaviour suggests
those are not holes.  However, the documentation gives a vague
explaination that says nils *might* be "holes".  But again,
judging by the actual behaviour, setting a particular entry in an array
to nil is not considered a hole.   I think that's probably a good
thing because it allows me to build an array and set some values to nil
as a placeholder.

However, if a change in implementation could change this behaviour that
makes me feel uneasy.  This whole issue makes me realize that Lua
really needs an official well defined language specification to be
taken seriously.

-- 
// Chris