Re: questions about Simple Cpp Binding

[Peter Shook <pshook@...>]

Hi Robert,

The first table is the table of methods, then luaL_newmetatable creates 
another table that is the metatable and puts it in the Lua Registry.
The end result is something like:

Lua Registry = {
  ...
  Account = {
    __metatable = <the method table>
    __index     = <the method table>
    __gc        = <the C function LuaAccount::gc_account>
  }
  ...
}

<the method table> = {
  deposit  = <the C function LuaAccount::deposit>
  withdraw = <the C function LuaAccount::withdraw>
  balance  = <the C function LuaAccount::balance>
}

It's okay to drop the tables off the stack once the structure is built 
because they are rooted in the Registry.  Some of the later examples 
also add the method table to the globals so that you can add methods 
written in a Lua script.

The __metatable field is returned by getmetatable in Lua scripts.
It isn't necessary.  The __index field is the important one.
See http://lua-users.org/lists/lua-l/2003-07/msg00103.html and the 
associated thread.

- Peter

Robert Kücken wrote:
> Hi,
> I have a few questions about the sample-code Simple Cpp Binding.
> I don't understand the register-function.
> First I create a new table in the stack, then I turn it into a metatable,
> right?
> But why I assign to __metatable the value of methodtable?
> And why I drop after this the metatable? First I create it and then I delete
> it?
> Hm, that's all, I hope, anyone can answer the questions.
> thank you
>
> robert kuecken