Re: Defining a function argument during index lookup

[Peter Shook <peter.shook@...>]

Peter Loveday wrote:
> 
> Is there a way I can insert an argument for a function during
> the index lookup handler of a table, where this lookup is returning
> a function?
> 
> I am trying to re-direct a function call from the global index
> handler to a userdata handler, based on a currently 'active'
> object.  The intention being that I can create a kind of 'using'
> directive :
> 
> obj:FuncA(...)
> obj:FuncB(...)
> obj:FuncC(...)
> 
> with:
> 
> UsingObj(obj)
> FuncA(...)
> FuncB(...)
> FuncC(...)
> 
> I have successfully set up the handler tables such that the global
> handler queries the active 'obj', and it will return FuncA (or whatever)
> as required.  However, I cannot find a way to simulate the ':', which
> magically inserts obj as the first argument... I have tried pushing
> multiple values on to the stack from my handler, but it doesn't seem
> to help.


The lastest version of Lua is great for stuff like this.

function class( t )
  t = t or {}
  t.index = t
  t.new = new
  return t
end

function new( class, init )
  init = init or {}
  return eventtable( init, class )
end

local eventtable, type
    = eventtable, type
    
local ind
function ind(t,i)
  return type( t[i] ) == 'function' and
    eventtable( {}, { settable=t, gettable=t, call=t[i] } ) or t[i]
end

function using( obj )
  eventtable( globals(), { index = function(t,i) return ind(obj,i) end }
)
end

A = class{
  data = 2
}

function A:pd(x)
  print( "x", x, "data", self.data )
end

function A:ps(x)
  print( "x", x, "stuff", self.stuff )
end

a = A:new{ stuff = 3 }
b = A:new{ stuff = 4 }

With the above you can do:

$ lua using.lua  -i
> using(a)
> = data,stuff
2       3
> = pd(11),ps(22)
x       11      data    2
x       22      stuff   3
nil
> using(b)
> = data,stuff
2       4
> = pd(33),ps(44)
x       33      data    2
x       44      stuff   4
nil
> 

Lua has always been a better extension language than Perl.  Now it's
just as good a scripting language.

- Peter