Re: C type conversion

[Asko Kauppi <askok@...>]

If I understood your question right, I would normally either use a  
table or a userdata with 'getindex' method, so that the struct fields  
can be read individually from Lua, without converting the whole  
structure (into a table).

My usage varies, about 50-50 between these approaches. Often, both  
will do the job.

You might ask things s.a.
- how many such objects do I have
- what is the lifespan, are they tossed around (good for userdata) or  
created ad hoc by Lua code as well (good for tables)
- are all fields needed (tables) or just some (userdata)

This should lead you on the right tracks, I hope.

Also, if you want to limit access (i.e. not allow any additional  
fields to be carried) then userdata. If you _wish_ additional fields  
to be carried, then table.

-asko


Chris kirjoitti 15.12.2006 kello 23.05:

> Is it generally better to perform type conversion before calling into
> Lua or after?
>
> For example, lets say I have some custom C structure and I want to get
> it into Lua.  I'm already in the C code and I'm going to be calling a
> function in Lua.   Is it better to convert the type into a Lua type
> and pass that into the lua_call() or would it be better to pass a raw
> pointer lightuserdata into Lua and then from within Lua call a C
> function to convert the type?
>
> Converting after calling into Lua seems to give a bit more safety
> because you're moving your call into Lua as soon as possible.
> However, the type needs to be converted from a C function anyway so it
> seems a little cleaner to convert it before you call into Lua.  Either
> method will work but I'm wondering if anyone has had experiences where
> one method was better for some reason or another.
>
> CR