Re: require one C module from another

[Josh Haberman <jhaberman@...>]

On Thu, Jun 19, 2014 at 2:26 PM, Aaron Faanes <dafrito@gmail.com> wrote:
> The safest solution IMO would be to write your luaopen_*
> to be resilient (or a no-op) in the face of redundant requires.
> If all they do are assignments to the global environment,
> this level of safety is easy to attain. I'd be curious to hear
> if this wasn't the case for you. :)

My C module keeps a weak table mapping (C pointer) -> (Lua wrapper).
This table is created in my luaopen function. So if my luaopen
function got called more than once, I would end up with more than one
table. That would be bad because I generally rely on the guarantee
that I have at most one Lua wrapper per C object.

I currently store this table in the registry, so I do have the option
of checking to see whether the table already exists when I create it.
But I think I should be able to store this as an upvalue of my C
functions instead if I choose (for example, if it gives better
performance). If I store the table as an upvalue (the equivalent of
declaring it as "local" in a pure Lua module), there would be no way
to do the right thing if my luaopen function gets called multiple
times.

> I guess I treat require's "load only once" ultimately as a very
> strong hint rather than as a fundamental guarantee - it's just
> too easy for the programmer to break.

It seems like an important guarantee if the module has any state.