Lua Table With "holes" example

gistfile1.txt

local empty_func = function() end
 --( Implement yourself:
 local assert_table = empty_func
 local is_number = function() return true end
 local is_integer = function() return true end
 --)

 local get_max_idx =
   function(t)
     assert_table(t)
     local result
     for k, v in pairs(t) do
       if is_number(k) and is_integer(k) then
         if not result or (k > result) then
           result = k
         end
       end
     end
     return result
   end

 local length_func =
   function(t)
     local mt = getmetatable(t)
     return mt.array_length
   end

 local to_array =
   function(t, length)
     length = length or get_max_idx(t) or 0
     setmetatable(
       t,
       {
         is_array = true,
         array_length = length,
         __len = length_func,
       }
     )
   end

 -- Demo:
 local t = {nil, nil, 3, nil, 5}
 to_array(t)
 for i = 1, #t do
   print(i, t[i])
 end