[help] complete Object Serialization?

Holonist · February 2015

Hi fellow Gideros users,

I know this has been asked (and answered as impossible before), but does anyone know how to serialize objects in Gideros?
Please read on before you give me the "repost-hammer".

I was working on a little "auto-battle rpg" game in LÖVE2D recently (I wasn't aware there is already such a genre, so it's a little disappointing I'm not the first one to do this).

However, in my project I have fairly complex classes/objects I need to be able to save. I give you a little pseudo-code to show you what I mean

class "Equippable":
- stat1
- stat2
- stat3
- func:changesomething()

class "Inventory":
- self={}
- func self:add(Equippable)

class "Player":
- stat1
- stat2
- stat3
- inventory = Inventory:new()
- self.equipment = {
Equippable:new()
Equippable:new()
Equippable:new()
}
- func:updateStats()
- func:xyz()

In reality the objects are even more complex and even Equippable has sub-objects called "manastones", which also have their own attributes and functions.

In LÖVE2D, i use a combination of "MiddleClass.lua" and "Lady.lua" (i think both are LÖVE specific) to save and load my player. For saving and loading the complete player object, I only have to write one line of code:
- lady_save_all("player.txt", player)
- player = lady_load_all("player.txt")

What lady does:
- it saves the object table recursively, (without any functions!)
- it adds the class name to the saved data
- it magically restores objects, no matter how complex, with completely functioning subobjects.

Because I want to port my game to Gideros, I would need something similar here. I tried JSON.encode, which is MOSTLY fine, but I lose my functions.

I tried to store all attributes in object.data (array), and when i load the game, initialize player and load player.data. Problem with this is, it doesn't work if my player contains subobjects like Equippable:new(), as those will be ignored by JSON.encode.

Any ideas, solutions? Should I try to use MiddleClass instead of Gideros class system and try to get Lady to work?

--
I will come back to edit the formatting of this post, unfortunately I have very little time atm.

Greetings to all!

Edit: One solution (even though it's not 'real' serialization) is attached in the zip below. It's a demo Gideros project that uses Lady to save an object, it's subojects and their functions (which aren't saved in the file, but correctly restored in runtime).

If you want to use it, you only have to copy MiddleClass.lua and Lady.lua, and the codeblock in my init.lua file. The rest is just the make the demo work.

ar2rsawseen · February 2015

Why it is not possible to serialize lua objects is that they might have C pointers in them.

But it should be possible to traverse the objects and collect all other data, create table with that data and serialize it.
Something like this could work

Maybe need to adjust more specific to some types (http://www.lua.org/pil/2.html)

function serialize(object, data)
    data = data or {}
    for i in pairs(object) do
        if type(object[i]) ~= "nil" and type(object[i]) ~= "thread" and type(object[i]) ~= "function"  and type(object[i]) ~= "userdata" then
            if type(object[i]) == "table" then
                data[i] = serialize(object[i], data)
            else
                data[i] = object[i]
            end
        end
    end
    return data
end

and then use either dataSaver module or save/load table

http://giderosmobile.com/forum/discussion/367/save-load-a-table/p1

Holonist · February 2015

Sorry, I don't really get your answer.
But surprisingly, porting Lady to Gideros was easier than I thought. I basically just had to replace the love-specific save mechanism

love.filesystem.write("file.txt", content)

to

file = io.open("file.txt", "w")
file:write(content)
file:close()

(same for loading.)

The magic that happens before saving/loading was apparently pure lua and is therefore usable in any framework.

With that obstacle out of the way, I think I'm going to be able to develop my game in Gideros. If anyone's interested, I can post the modified Lady.lua and instructions how to use it.

talis · February 2015

@holonist It will be a great contribution . =D>

Holonist · February 2015

I added a zip file with a prepared gideros project.
Please try it and let me know what you think.

pie · February 2015

@Holonist thank you it's really cool!

not just the lady port but the whole project:
I was wondering where to start to learn a proper use of classes (actually I use them as a monkey can use a calculator

|) ) , and I think that now I do..

I have a question about "middleclass.lua": what does it do exactly? What are the differences/advantages from creating new classes as in

testClass = Core.class()
function testClass:init() 
...blah blah.. 
end

?

Thank you

Holonist · February 2015

I don't know if there are any advantages.

It is necessary for Lady to work, so make sure you use middleclass for every object you want to serialize with Lady. (you can make it work with other class systems, but I don't know how to be honest).

For everything that doesn't have to be saved accurately, like buttons, sprites etc, I would recommend to use the Gideros class system, because otherwise you can't inherit easily from Sprite, EventDispatcher, etc.

Fortunately, you can use both class mechanisms in the same project (at least i didn't find incompatibility yet).

Edit:
One tip, if you want to use inheritance with middleclass, you do it like this.

Person = class('Person')
 
function Person:initialize(name, age)
	self.name = name
	self.age = age
end
 
function Person:getOlder()
	self.age = self.age+1
end
 
 
BusinessMan = class('BusinessMan', Person) --important to get this line right
 
function BusinessMan:initialize(name, age, hobby)
	Person.initialize(self, name, age) --important to get this line right too
	self.hobby = hobby
end
 
function BusinessMan:sayHello()
	print("Hello, I'm a businessman, my hobby is " .. self.hobby)
end

BusinessMan will have access to the same fields and functions that Person has.

In Gideros it functions similarly, but you can find that in the forums.
(Also, you will find additional info to Middleclass on their github page)

Holonist · February 2015

Another thing. If you want to produce, let's say 100 Businessmen.

You can do it like this:

for i=1, 100 do
	local a = BusinessMan:new("somename", i, "somehobby")
end

but please, don't because you will have no way to access those objects later.

do it like this:

businessMen = {}
 
for i=1, 100 do
	businessMen[i] = BusinessMan:new("somename", i, "somehobby")
end

This way you can track/manipulate your objects later on.
Not getting this right gave me huge problems for a long time, therefore i mention it. Otherwise sorry for messing up the thread :P

pie · February 2015

Thank you,
about the last tip: good point writing it down.
I already figured that out some time ago, but I wish I found it somewhere before wasting all that time..

) - it is the same using gideros Class system.

businessMen = {}
could also be local if your tracking needs are in the same scope

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