Re: [ANN] Lua 5.3.0 (alpha) now available

[Dirk Laurie <dirk.laurie@...>]

2014-08-01 20:47 GMT+02:00 Andrew Starks <andrew.starks@trms.com>:

> On Fri, Aug 1, 2014 at 1:00 PM, Roberto Ierusalimschy
> <roberto@inf.puc-rio.br> wrote:
>>
>> > It was mentioned that "table.clear" (or similar) was likely. Was it
>> > decided
>> > that it would not be useful?
>>
>> I don't think we even agreed on what it would do.
>>
>> -- Roberto
>>
>
> The only negative I found was disagreement on why one would want it.
>
> Primary example:
>
> Shared state container between two entities that needs to be reset. As it
> is, the solution would be to store the state inside another table and
> replace that table. It'd might be better to clear it, thus creating less
> trash and allowing me to more concisely represent what i'm doing.
>
> Another example, which was the source of comment by Mike:
>
> A pretty printer that needs to track tables that have already been
> traversed. I would store the tostring(t) (assuming no __tostring) in a table
> as `visited[tostring(t)] = true`.
>
> When done, I would clear the table. As it is, i would make the table new,
> every time because I would assume that looping and nilling the values would
> take more time that trashing the table.

If there is no API function for this, then there is no call for having
it in Lua.

What would such an API function do? Traverse the whole table and
set every value to nil, in order to adjust the reference count. It's not
obvious that the performance enhancement relative to

for k in pairs(tbl) do tbl[k]=nil end

is worth yet another library function in a language that can't even carry
the baggage of cosh, sinh and tanh.