Re: new "empty" value/type in Lua?

[Luis Carvalho <lexcarvalho@...>]

> Is something like this enough? (Note that 'n' is *not* hidden; I do
> not think hidden stuff is good in the end...)

Agreed. I had a very similar version, but required that only integer keys can
be set in __newindex and setlength is implemented through __call:


local type, floor, pack, setmetatable, rawset =
  type, math.floor, table.pack, setmetatable, rawset

_ENV = nil

local nexti = function (t, i)
  if i < t.n then
    i = i + 1
    return i, t[i]
  end
end

local mt = {
  __len = function (t) return t.n end,
  __ipairs = function (t) return nexti, t, 0 end,
  __newindex = function (t, k, v)
    if type(k) == "number" and k > 0 and k == floor(k) then
      if k > t.n then t.n = k end -- grow?
      return rawset(t, k, v)
    end
  end,
  __call = function (t, n) -- resize?
    if type(n) == "number" and n >= 0 and n == floor(n) then
      if n < t.n then
        for i = n + 1, t.n do t[i] = nil end -- clean up
      end
      t.n = n
    end
    return t.n
  end,
}

return function (...)
  return setmetatable(pack(...), mt)
end


Cheers,
Luis


-- 
Computers are useless. They can only give you answers.
                -- Pablo Picasso

-- 
Luis Carvalho (Kozure)
lua -e 'print((("lexcarvalho@NO.gmail.SPAM.com"):gsub("(%u+%.)","")))'