Re: table.unpack(...) and the __index metamethod

[Tim Hill <drtimhill@...>]

On Jun 13, 2014, at 11:00 PM, Coda Highland <chighland@gmail.com> wrote:

> On Fri, Jun 13, 2014 at 10:37 PM, Tim Hill <drtimhill@gmail.com> wrote:
>> 
>> On Jun 13, 2014, at 5:22 PM, Thiago L. <fakedme@gmail.com> wrote:
>> 
>>>> 
>>>> No, the OP pointed out that the overhead of doing the metamethod test in table.unpack() is low, since it can be done once at the start of unpack(), which then chooses a (fast) rawgeti() based loop or a (generic) index metamethod loop. So you get the best of both worlds in one API.
>>>> 
>>>> —Tim
>>>> 
>>> What if we want raw unpacking of metatabled tables? (aka keep nil as nil)
>> 
>> 1. Save metatable from table
>> 2. Set metatable on table to nil
>> 3. Unpack it
>> 4. Restore metatable
>> 
>> —Tim
>> 
>> 
> 
> Until someone sets __metatable.
> 
> /s/ Adam
> 

Which is a clear indication they don’t want to allow back-door access :)

Anyway, I’m not tied to this but I still think the OP had a good point. The Lua ref notes in a couple of places the raw accesses are done for speed, but he is correct in noting that you don’t need to sacrifice non-raw access for speed in this case.

—Tim