From: Graham Wakefield
<wakefield@mat.ucsb.edu>
To: Lua mailing list <lua-l@lists.lua.org>
Sent: Wednesday, March 28, 2012 3:38 PM
Subject: Re: callstack recursive environment
On Mar 28, 2012, at 11:46 AM, Steve Litt wrote:
> It sounds to me, from your words above, that all globals go in _G. Now
> watch this...
>
> Give _G a metatable that, when you're in diagnostic mode, errors out on
> every global not specifically declared in _G's metatable ...
> SteveT
>
I think what you are describing is what strict.lua does, more or less:
--
-- strict.lua
-- checks uses of undeclared global variables
-- All global variables must be 'declared' through a regular assignment
-- (even assigning nil will do) in a main chunk before being used
-- anywhere or assigned to inside a function.
--
local getinfo, error, rawset, rawget = debug.getinfo, error, rawset, rawget
local mt = getmetatable(_G)
if mt == nil then
mt = {}
setmetatable(_G, mt)
end
mt.__declared = {}
local function what ()
local d = getinfo(3, "S")
return d and d.what or "C"
end
mt.__newindex = function (t, n, v)
if not mt.__declared[n] then
local w = what()
if w ~= "main" and w ~= "C" then
error("assign to undeclared variable '"..n.."'", 2)
end
mt.__declared[n] = true
end
rawset(t, n, v)
end
mt.__index = function (t, n)
if not mt.__declared[n] and what() ~= "C" then
error("variable '"..n.."' is not declared", 2)
end
return rawget(t, n)
end
