Re: Prevent table insertions?

[Luis Carvalho <carvalho@...>]

> I'm looking to find a way to prevent new values from being entered
> into a table. I tried the read-only table approach from PIL
> (http://www.lua.org/pil/13.4.5.html) which works as advertised.
> However, I can still insert values like:
> 
>  table.insert(days, "Frankday")
> 
> Any suggestions?

You can use a userdata proxy:

function readonly(t)
  local u = newproxy(true)
  local mt = getmetatable(u)
  mt.__index = t
  mt.__newindex = function()
    error("attempt to update a read-only table", 2)
  end
  mt.__len = function() return #t end
  -- emulate __pairs
  mt.__call = function() return next, t, nil end
  return u
end

Cheers,
Luis.

-- 
A mathematician is a device for turning coffee into theorems.
        -- P. Erdos 

-- 
Luis Carvalho
Applied Math PhD Student - Brown University
PGP Key: E820854A <carvalho@dam.brown.edu>