Chacks if t is an array

is_array.lua

local function tbl_copy(t)
  if type(t) ~= "table" then
    return t
  end
  
  local res = {}
  for k, v in pairs(t) do
    res[k] = tbl_copy(v)
  end
  
  return setmetatable(res, getmetatable(t))
end

local function is_array(t)
  local _t = tbl_copy(t)

  for i = 1, #t do
    if _t[i] == nil then
      return false
    end
    _t[i] = nil
  end

  if next(_t) then
    return false
  end

  return true
end