etc/strict.lua

   1 --
   2 -- strict.lua
   3 -- checks uses of undeclared global variables
   4 -- All global variables must be 'declared' through a regular assignment
   5 -- (even assigning nil will do) in a main chunk before being used
   6 -- anywhere or assigned to inside a function.
   7 --
   8
   9 local getinfo, error, rawset, rawget = debug.getinfo, error, rawset, rawget
  10
  11 local mt = getmetatable(_G)
  12 if mt == nil then
  13   mt = {}
  14   setmetatable(_G, mt)
  15 end
  16
  17 mt.__declared = {}
  18
  19 local function what ()
  20   local d = getinfo(3, "S")
  21   return d and d.what or "C"
  22 end
  23
  24 mt.__newindex = function (t, n, v)
  25   if not mt.__declared[n] then
  26     local w = what()
  27     if w ~= "main" and w ~= "C" then
  28       error("assign to undeclared variable '"..n.."'", 2)
  29     end
  30     mt.__declared[n] = true
  31   end
  32   rawset(t, n, v)
  33 end
  34
  35 mt.__index = function (t, n)
  36   if not mt.__declared[n] and what() ~= "C" then
  37     error("variable '"..n.."' is not declared", 2)
  38   end
  39   return rawget(t, n)
  40 end
  41