Lua - List Serialization

Serialization refers to converting data into streams of data/characters. Once data is saved into bytes/characters, we can save the bytes/characters to a file or send over network. In this chapter, we'll see how to serialize various types of Lua data and Lua List.

Serialize Data

Following code showcases the code to serialize the data.

-- Opens a file in write
file = io.open("test.txt", "w")

-- sets the default output file as test.lua
io.output(file)

-- function to serialize an object
function serialize (o)

   local objType = type(o)
   -- if object is of type number
   if objType == "number" then
      -- serialize the number
      io.write(o)
   -- if object is of type string
   elseif objType == "string" then
   -- serialize the string after sanitizing the same
      io.write(string.format("%q", o))
   else
      -- iterate throgh entries
      for v in o:iterator() do
         serialize(v[1])
         io.write(",")
      end
   end
end

Deserialize data

Following code showcases the code to deserialize the data.

-- Opens a file in read
file = io.open("test.l", "r")

-- sets the default input file as test.lua
io.input(file)

-- function to deserialize the object
function deserialize(){
  local data = io.read()
  return data
}

Example - Serialize a List

Following code showcases the code to serialize the data.

main.lua

-- Opens a file in read
file = io.open("test.txt", "w")

-- sets the default output file as test.lua
io.output(file)

-- function to serialize an object
function serialize (o)
   local objType = type(o)
   -- if object is of type number
   if objType == "number" then
      -- serialize the number
      io.write(o)
   -- if object is of type string
   elseif objType == "string" then
   -- serialize the string after sanitizing the same
      io.write(string.format("%q", o))
   else
      -- iterate throgh entries
      for v in o:iterator() do
         serialize(v[1])
         io.write(",")
      end
   end
end


-- List Implementation
list = {}
list.__index = list

setmetatable(list, { __call = function(_, ...)
   local t = setmetatable({ length = 0 }, list)
      for _, v in ipairs{...}
         do t:push(v)
      end
      return t
   end })

-- push an element to the end of the list
function list:push(t)
   -- move till last node
   if self.last then
      self.last._next = t
      t._prev = self.last
      self.last = t
   else
      -- set the node as first node
      self.first = t
      self.last = t
   end
   -- increment the length of the list
   self.length = self.length + 1
end

-- iterate through the list
local function iterate(self, current)
   if not current then
      current = self.first
   elseif current then
      current = current._next
   end

   return current
end

function list:iterator()
   return iterate, self, nil
end


days = list({"Monday"},{"Tuesday"}, {"Wednesday"},{"Thursday"},{"Friday"},{"Saturday"},{"Sunday"})

serialize(days)

Output

Now open test.txt to verify the following output:

"Monday","Tuesday","Wednesday","Thursday","Friday","Saturday","Sunday",

Example - Deserialize a List

Following code showcases the code to deserialize the data.

main.lua

-- Opens a file in read
file = io.open("test.txt", "r")

-- sets the default input file as test.lua
io.input(file)

days = {}

input = io.read()

-- for each line
for entry in string.gmatch(input, "([^,]+)") do
   -- add the entry to days
   days:push({entry})
end

-- iterate throgh entries
for v in days:iterator() do
   print(v[1])
end

Output

When we run the above code, we will get the following output−

"Monday"
"Tuesday"
"Wednesday"
"Thursday"
"Friday"
"Saturday"
"Sunday"