Re: [ANNOUNCE] Lua 5.0 (alpha) now available

["David Burgess" <david@...>]

Many thanks. What sort of speed improvement are we looking at?
DB

> >Are we going to document lua_boxpointer?
>
> In Lua 5.0 we cleaned up the confusion of what a userdata is and how it is
> created: userdata are Lua objects created with lua_newuserdata:
>
> LUA_API void *lua_newuserdata (lua_State *L, size_t size);
>
> lua_newuserdata creates an object that has an attached buffer of the given
> size; this buffer is returned to the host program and can be written to.
> Lua never looks inside the buffer, but userdata objects, like all other
objects,
> are subject to garbage collection. In other words, lua_newuserdata gives
> you a buffer that you don't have to worry about mallocing or freeing, but
> which you can used to store whatever you want, even dynamically changing
its
> contents.
>
> lua_boxpointer covers the common case of wanting to store a pointer in
this
> buffer. lua_unboxpointer gets the pointer from the buffer of the given Lua
> object. A typical use is to store the pointer of a C struct that has to be
> exported to Lua so that it can have a metatable. Only userdata created
with
> lua_newuserdata can have metatables. Note also that lua_boxpointer will
> return a different Lua object each time it is called, even if the same
pointer
> is used.
>
> Lua 5.0 also introduced "light" userdata, which are pointers treated as
values,
> not as objects. Light userdata is more like numbers: no memory is
allocated,
> except the Lua value struct where all Lua values reside. On the other
hand,
> "light" userdata cannot have metatables. Two "light" userdata values are
the
> same iff their pointers are the same.
>
> We think this scheme is clear and makes userdata both flexible and fast.
> --lhf
>