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I have some code that looks like this:

debug.setmetatable("", {__index=function(o,k)
  local mt = metatables[coroutine.running()].string
  if mt then
    local __index = rawget(mt, "__index")
    if type(__index) == "function" then
      return __index(o,k)
      return __index[k]

It takes the metatables for the basic Lua types (string, number, nil, etc) and replaces them with a proxy metatable. This proxy metatable forwards to a different table based on the currently running coroutine. This gives me virtualization of those metatables.

It's really slow (3-4x slower[1] than the default string metatable) and I'd like to make it faster. Is that possible?

[1] - I haven't actually benchmarked it, but default string metatable gives about 2 table accesses per operation; this thing does at least 8 when using globals, and that doesn't take into account interpreter overhead and all the function calls!

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