RE: user data

["Thijs Schreijer" <thijs@...>]

> -----Original Message-----
> From: lua-l-bounces@lists.lua.org [mailto:lua-l-bounces@lists.lua.org] On
> Behalf Of Philipp Kraus
> Sent: zaterdag 1 december 2012 12:47
> To: Lua list mailing
> Subject: user data
> 
> Hello,
> 
> I have found in the C reference of Lua the functions lua_islightuserdata
> lua_isuserdata
> 
> What is the "user data" ? Eg I have got a Lua function that returns
something,
> which datatype should I return, so one of these function will be true.
> How can I handle "user data" in C ?

Userdata is a c-side type (cannot be created in Lua, only passed to it).  It
allows to represent an arbitrary chunk of memory in lua and pass it around
as a lua value. By attaching a metatable you can provide lua with a simple
means to perform actions on it. (btw; light user data is just a pointer, but
is important on equality)

Check out the relevant part in PiL http://www.lua.org/pil/28.html