Re: Redefine "=".

["Alexey Zaytsev" <alexey.zaytsev@...>]

On 6/2/06, Jérôme VUARAND <jerome.vuarand@gmail.com> wrote:
> t = {}
> setmetatable(t, {
>   __newindex = function(self, key, value)
>     print("Hello World! ("..key..value..")")
>   end
> })
>
> t["foo"] = "bar"
> > Hello World! (foobar)
>
> There is a strong distinction between variables and values in Lua.
> Variables are merely references to values. In :
> t = "foo"
> you are not affecting a value to the above table, you are affecting a
> new value to an untyped variable (t). But you cannot set metatable for
> variables, only for values. That's a good reason for not having a kind
> of __reference or __copy metamethod.

The __reference metamethod would not operate on variable t, but rather on the
value, which is going to be assigned to this variable. like:

t = {}
setmetatable(t, {
 __ref = function(table)
  return table
}) <- the normal behaviour

setmetatable(t, {
 __ref = function(table)
   local tmp = {}
   for i, j in pairs(table) do
     tmp[i] = j
   end
   return tmp
 end
}) <- make "=" behave like copy.

> 2006/6/1, Alexey Zaytsev <alexey.zaytsev@gmail.com>:
> > Hello.
> >
> > Is it possible to redefine the reference ("=") operator for tables in lua?
> > I thougth it is a job for metamethods, but could not find any. Is
> > there any reason for not having any __reference (or __copy) metamethod
> > in lua?
> >