Re: Bug report in length of simple table

[Oliver Kroth <oliver.kroth@...>]

Am 13.09.2016 um 11:37 schrieb Malma:
> I think this explanation must be in official doc if it's a source of 
> confusion.
>
> print(# {[1] = 10, [2] = 20, [3] = nil, [4] = nil, [5] = 40} ) -- is 
> not sequence ?
> print(# {10, 20, nil, nil, 40} ) -- is sequence ?  From doc: Note that 
> a table like {10, 20, nil, 40}  is not a sequence...
>
> output:
>
> 2
> 5
The # operator computes the number of elements of a sequence in a Lua table
# returns a valid result only for sequences.

A Lua table contains a sequence if and only if all integer keys greater 
zero are contiguous; i.e. there must be no missing numbers.

If there are gaps, the table contains no sequence.

Th table may contains values for other keys, including 0, negative, or 
non-integer numbers, this does not affect the sequence.

Note that this definition is completely independent of the 
implementation detail has part / array part; one does not need to care 
about that.
It's only about integer keys.

nil can't be stored in a table. Assigning nil to a table key removes the 
key. Use another value to tag special (e.g.missing) entries, like false

{10, 20, nil, nil, 40} contains NOT a sequence
{10, 20, false false, 40] contains a sequence
{ [0]="null", 10, 20, 30, a="alpha",  [math.pi] = "pi" } contains a sequence

--
Oliver