Re: PiL2, ch 28.3: Adding Lua methods to an array?

[Javier Guerra <javier@...>]

On Friday 09 June 2006 3:35 am, Carsten Fuchs wrote:
> Hello all,
>
> when we have userdata with a metatable as described in the "array"
> example in the PiL1 or PiL2, chapter 28.3 "Object-Oriented Access"
> (http://www.lua.org/pil/28.3.html), I would like to be able to add more
> functions in Lua.
>
> For example, chapter 28.3 in PiL2 starts with the example
>
> a = array.new(1000)
> print(a:size())
> a:set(10, true)
> print(a:get(10))
>
> And now I'd like to be able to add a statement like
>
> function a:OnMouseClick()
>      -- do something...
>      print("Hello!\n")
> end

your object 'a' is a userdata; but it has a metatable already set, and i guess 
its __index field points to the methods table.  so, you can write:

local m = getmetatable (a).__index

function m:OnMouseClick()
   .........
end

maybe even:

function getmetatable (a).__index:OnMouseClick()
   .......
end


another thing you could try is to use __newindex:

local mt = getmetatable (a)
function mt.__newindex (t,k,v)
   t.__index[k] = v
end

after that, any value you set like "a[xx] = yy" will be set on the methods 
table, therefore this could work:

function a:OnMouseClick ()
   ......
end


-- 
Javier

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