RE: Generalized pairs, was Re: linking tables to C++ objects?

["Jerome Vuarand" <jerome.vuarand@...>]

Rici Lake wrote:
> On 26-Feb-07, at 7:31 PM, Graham Wakefield wrote:
>> Yes, I've been trying this approach today; mapping __index and
>> __newindex metamethods of the userdata to the userdata environment
>> table. A disadvantage of this is that in Lua my object behaves as a
>> table for general use, but not as a table for functions such as
>> table.foreach() and generic for, which could be confusing for end
>> users.  Is there a way to implement a next() method for the generic
>> for construction?
> 
> The main issue with implementing this in Lua is not efficiency (even
> table.foreach isn't bad). The problem is that the metatable might
> (quite reasonably) be locked with a __metatable key, and that would
> prevent us from actually getting at the __pairs pseudo-metamethod.
> Implementing it in C avoids that problem.

Actually people securing userdata metatables can set the __metatable
field to a table instead of just false or some locking value, and then
expose __pairs (and eventually other) metamethod(s) to Lua. Since pairs
is meant to be a helper to manipulate the userdata it's normal to make
it available to code manipulating that userdata.