Re: Luajit cdata with metatables....

[Daurnimator <quae@...>]

On 31 March 2011 01:54, Daurnimator <quae@daurnimator.com> wrote:
> (sorry, this question was sent to old list address; and was meant to
> be posted before my follow up question: "luajit FFI cdata problem")
>
> Hi List,
>
> I had a search of the list archives and nothing came up on the topic...
>
> I would like to attach metamethods to some luajit2 ffi cdata
> objects... Whats the best way to go about this?
>
> eg:
> local foo = ffi.new("int[3]",5,6,7)
> local t = { [0]=x , y , z }
> setmetatable(foo,{__index=function(ob,key) return ob[t[key]] end })
>
> First thought to come to mind is newproxy... but luajit probably has a
> smarter/better way?
>
> Daurn.
>
> Addendum:
> I was trying to use 2 tables as a back and forth conversion of cdata
> and userdata; but cdata as keys in a table seems to be a bad idea.
> local edge_methods = {} -- methods to support.
>
> local tocdata = setmetatable ( { } , { __mode = "k" } )
> local touserdata
>        touserdata = setmetatable ( { } , {
>                        __mode = "kv" ;
>                        __index = function ( t , cdata )
>                                local v = newproxy ( true )
>                                getmetatable ( v ).__index = function ( udata , k )
>                                        local method = edge_methods [ k ]
>                                        if method then
>                                                return method
>                                        else
>                                                local cdata = tocdata [ udata ] [ k ]
>                                                local udata = touserdata [ cdata ]
>                                                return udata
>                                        end
>                                end
>                                getmetatable ( v ).__newindex = function ( udata , k , v )
>                                        tocdata [ udata ] [ k ] = v
>                                end
>                                getmetatable ( v ).__tostring = function ( udata )
>                                        return "Dart" .. tostring ( tocdata [ udata ] ):match("cdata(<.*>)")
>                                end
>
>                                tocdata [ v ] = cdata
>                                rawset ( t , cdata , v )
>                                return v
>                        end ;
>                } )
>

Anyone care to help?

Daurn