Re: local variables and scope

[Kriss <Kriss@...>]

Just to throw in an alternative setup since this stuff although trivial 
code is a non trivial design decision and I didn't find much discussion 
when I searched for it before implementing.

Essentially I'm doing the same but rather than keeping a table of 
allowed globals I'm just using rawset with some sugar.

Creating a table called global that has a __newindex metatable function 
that translates into rawset on _G , IE its just sugar for rawset.

So whenever I really want to have the ability to create a global var, 
which is obviously not very often I use global.this="that"

Which to my mind reads well since intended global creations are obvious 
from reading the source but that's personal preference. Probably because 
I'm using  a number of  lua modules that get loaded and unloaded 
changing the available globals during the life of the program.

This is what I'm using and so far it doesn't seem to have any obvious 
problems.

---

local g = {

   __newindex_lock = function ()    -- set error function
       local mt=getmetatable(_G)
           if not mt then
               mt={}
               setmetatable(_G,mt)
           end
           mt.__newindex = function(t,i,v)
               error("cannot create global variable `"..i.."'",2)
           end
       end
   ,
   __newindex_unlock = function ()    -- clear error function
       local mt=getmetatable(_G)
           if mt then
               mt.__newindex = null
           end
       end

   }

   setmetatable(g, {
     __index=function(t,i) return rawget(_G,i) end,
     __newindex=function(t,i,v) rawset(_G,i,v) end,
   })

global=g
global.__newindex_lock()

--

Kriss

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