Re: lua-5.1-alpha: length operator on tables (arrays) and nil values

[Chris Marrin <chris@...>]

Bilyk, Alex wrote:
> I also find this a problem, at least for myself. We have all sorts of
> explanations why such is the behaviour of #, but It's just plain
> counterintuitive to say the least. If not going into reading the
> manual as to why such is the behavior, the results produced by the
> cases below make no sense whatsoever and seem totally random. This
> doesn't click well in my mind with the bulk of Lua, which I find
> rather simple and intuitive.
>
> I think the problems stem from the fact that a vector and a hash
> under the hood are presented at language level as a single concept of
> a 'table'. It would be easier to implement and maintain, it seems,
> two separate language concepts of a vector and a hash, rather then
> doing all sorts of acrobatics in attempts to present them via a
> single language construct.

I apologize if this just adds noise to the conversation. But the way 
Javascript defines this is with a length property. If you ever add a 
numeric property to the object, it checks it against the length property 
and if it is greater, it sets length to i+1 (because Javascript starts 
indexes at 0). If, for instance, you add index 5 to an empty Array 
object, indexes 0-4 will be nil and the length will be 6. You can set 
and get length as well. Setting length to 4 on an empty object makes it 
have indexes 0-3, all with nil values. Setting length to less than its 
current value destroys all indexes at or above that new size.

This can be added on top of standard Lua, of course. In fact, when I 
switched to 5.1 last week, this is exactly what I did. It works fine 
and, since I do all the length fiddling on the C++ side, it is very 
fast. I still use lua_obj() to find out the size of a table that is 
being passed into one of my objects, but that is about it.

To me, the # operator and the lua_objlen() function are simply a 
convenient way to search for the last numeric property of an object.

--
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