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  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.  
  42.