what is actual implementation of lua __pairs?

Question

Does anybody know actual implementation of lua 5.2. metamethod __pairs? In other words, how do I implement __pairs as a metamethod in a metatable so that it works exactly same with pairs()?

I need to override __pairs and want to skip some dummy variables that I add in a table.

Answer 1

The following would use the metatable meta to explicitly provide pairs default behavior:

function meta.__pairs(t)
  return next, t, nil
end

Now, for skipping specific elements, we must replace the returned next:

function meta.__pairs(t)
  return function(t, k)
    local v
    repeat
      k, v = next(t, k)
    until k == nil or theseok(t, k, v)
    return k, v
  end, t, nil
end

For reference: Lua 5.2 manual, pairs