Lua 5.2 sequence definition - clarification needed

[Lorenzo Donati <lorenzodonatibz@...>]

Hi all!

* 1st point

Section 3.4.6 of Lua 5.2 refman says:

"Unless a __len metamethod is given, the length of a table t is only 
defined if the table is a sequence, that is, the set of its positive 
numeric keys is equal to {1..n} for some integer n."

and later:

"Note, however, that non-numeric keys do not interfere with whether a 
table is a sequence."


From the first sentence I get that also non-positive numeric keys don't 
interfere with the table being a sequence (right?). Wouldn't it be worth 
adding this note to the second sentence? I.e.:

"Note, however, that non-numeric keys *or non-positive numeric keys* do 
not interfere with whether a table is a sequence."


* 2nd point

This is maybe nitpicking, but anyway:

as someone else already pointed out in an old thread (IIRC), the first 
cited sentence above assumes that an empty sequence is a table that has 
no positive numeric keys. In this case the above definition would hold 
with the set being {1..0}, i.e. the empty set. But the empty set could 
also be represented as {1..-1}, or {1..-4} with that notation. Therefore 
someone could infer that for empty sequences the length could be either 
0, -1 or -4.

Therefore I would modify slightly the definition:

"Unless a __len metamethod is given, the length of a table t is only 
defined if the table is a sequence, that is, the set of its positive 
numeric keys is equal to {1..n} for some *non-negative* integer n."

This would rule out that (admittedly unintuitive, but correct) 
misinterpretation.

Cheers.
-- Lorenzo