Re: Interesting stack overflow in Lua 5.3

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

2015-09-04 4:12 GMT+02:00 Tim Hill <drtimhill@gmail.com>:
>
> On Sep 3, 2015, at 11:12 AM, Sean Conner <sean@conman.org> wrote:
>
> The following function, when invoked, causes a C stack overflow
> in Lua 5.3.
>
> local subsystem_mt = {__index =
>   function(spec,auction)
>      for key,bid in ipairs(spec) do
>         print("Checking '"..auction.."' against '"..key.."'")
>      end
>   end}
>
>
> I may be missing something, but "The following function" does not seem
> to be a function. It looks like a table... (Therefore, I do not know
> how to invoke it to cause something.)
>
>
>  All I did was take that code, then add
>
> x = setmetatable({},subsystem_mt)
> print(x.one)
>
>
> Isn’t this expected behavior? Since ipairs() respects metamethods (since
> 5.3), looks like you have an infinite recursion (if you don’t have an item
> at key 1)?

The unexpected part is that you _always_ have an infinite recursion.
Sheldon Cooper and Don Tillman would have seen this immediately,
of course. For others, a little hint in the manual, where __index is being
documented, would be useful.