private int command(LuaCallFrame callFrame, int nArguments) {
      BaseLib.luaAssert(nArguments >= 1, "insufficient arguments for Command");
      String cmd = (String) callFrame.get(0);
      if (cmd != null && cmd.length() == 0)
        cmd = null;
      Engine.ui.command(cmd);
      return 0;
    }
Distance object's fake GetValue or __call method

Called from Lua code: dist:GetValue("metres") or dist("ft"),
where 'dist' is double, converts the number to specified units
and returns as double.
main/src/main/java/cgeo/geocaching/wherigo/openwig/WherigoLib.java