Re: how to handle # operator for proxy tables?

[Valerio Schiavoni <valerio.schiavoni@...>]

So, the way I did it is using newproxy, but is there something safer to do ?

proxytable = function (orig)
	local p = newproxy(true)  -- create proxy object with new metatable
	getmetatable(p).__len = function() return #orig end
	getmetatable(p).__newindex=function(p,k,v)
								rawset(orig,k,v);
								if (k==1) then
									print("do something")
								end
								end
	getmetatable(p).__pairs = function(t) return pairs(orig)end
	return p
end

On Tue, Jun 8, 2010 at 4:18 PM, Valerio Schiavoni
<valerio.schiavoni@gmail.com> wrote:
> hello,
> i use proxy tables to catch modifications on 1st elements of a table:
>
> proxytable = function ( orig )
>        return setmetatable({},
>                {
>                __index=orig,
>                __newindex=function(t,k,v)
>                                rawset(orig,k,v);
>                                        if (k==1) then
>                                                print("do something")
>                                        end
>                                end,
>                __len=function(t) return #orig end,
>                __pairs = function(t) return pairs(orig)end })
>                end
>
> t={1,2,3,4}
> print(#t)
> t=proxytable(t)
> print(#t)
>
> The problem is that the i was expecting the 2nd call to #t to return 0.
> How can I get around this?
>
> It seems Lua5.2 will handle this:
> http://www.batbytes.com/luafaq/#T8.2.5, but for now I'm stuck with
> 5.1.4.
>
> Thanks
> Valerio
>