Datastore.read always returning nil

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1

Hi all,
I'm using SDK 1.10 (Windows, LUA using the emulator), and trying something very basic with datastore, which is to store a table and them immediately load it (and yes Hungarian notation works for me):

function fSaveMap(fvMap)
	playdate.datastore.write(rHexList,fvMap,true)
end

function fLoadMap(fvMap)
	rHexList = playdate.datastore.read(fvMap)
end

The save works fine and the json file is as I'd expect it to look. However whenever I try to load it, it always comes back nil. I've tried simplifying the table and turning off the prettification when saving (and I'm calling , but no dice. I'm at a loss because of how straightforward this all seems like it should be. Are there any other limitations here of which maybe I'm not aware?

2

Perhaps you could share the name and contents of the resulting json file, too?
Is the value of fvMap equal for both save and write? I would just add a print(rHexList,fvMap,true)
and print(fvMap) to sanity-check what values are being used. Note that in lua, nil values are happily accepted without throwing errors in most situations

3

Sure, here's the file as it's saved. Name is testmapsave.json, and I'm calling it to test this out right after randomly generating a hex map. Write works fine, but the Read never does. I've already done printouts to ensure values are going in and out correctly, but as soon as I try the Read, whatever I return it into is nil.

fMapRandGen()
fSaveMap("testmapsave")
fLoadMap("testmapsave")

[
	 {
		"class":2,
		"image":"userdata 00000169B0E52A48",
		"occupant":0,
		"open":-1,
		"range":0,
		"x":-5,
		"y":0,
		"z":5
	},
	 {
		"class":5,
		"image":"userdata 00000169B0E52578",
		"occupant":0,
		"open":-1,
		"range":0,
		"x":-5,
		"y":1,
		"z":4
	},
	 {
		"class":3,
		"image":"userdata 00000169B0E52EA8",
		"occupant":0,
		"open":-1,
		"range":0,
		"x":-5,
		"y":2,
		"z":3
	},
	 {
		"class":4,
		"image":"userdata 00000169B0E525E8",
		"occupant":0,
		"open":-1,
		"range":0,
		"x":-5,
		"y":3,
		"z":2
	},
	 {
		"class":7,
		"image":"userdata 00000169B0E527A8",
		"occupant":0,
		"open":-1,
		"range":0,
		"x":-5,
		"y":4,
		"z":1
	},
	 {
		"class":1,
		"image":"userdata 00000169B0E52738",
		"occupant":0,
		"open":-1,
		"range":0,
		"x":-5,
		"y":5,
		"z":0
	},
	 {
		"class":7,
		"image":"userdata 00000169B0E527A8",
		"occupant":0,
		"open":-1,
		"range":0,
		"x":-4,
		"y":-1,
		"z":5
	},
	 {
		"class":5,
		"image":"userdata 00000169B0E52268",
		"occupant":0,
		"open":-1,
		"range":0,
		"x":-4,
		"y":0,
		"z":4
	},
	 {
		"class":6,
		"image":"userdata 00000169B0E52F18",
		"occupant":0,
		"open":-1,
		"range":0,
		"x":-4,
		"y":1,
		"z":3
	},
	 {
		"class":8,
		"image":"userdata 00000169B0E52B98",
		"occupant":0,
		"open":-1,
		"range":0,
		"x":-4,
		"y":2,
		"z":2
	},
	 {
		"class":6,
		"image":"userdata 00000169B0E522D8",
		"occupant":0,
		"open":-1,
		"range":0,
		"x":-4,
		"y":3,
		"z":1
	},
	 {
		"class":1,
		"image":"userdata 00000169B0E52738",
		"occupant":0,
		"open":-1,
		"range":0,
		"x":-4,
		"y":4,
		"z":0
	},
	 {
		"class":1,
		"image":"userdata 00000169B0E52738",
		"occupant":0,
		"open":-1,
		"range":0,
		"x":-4,
		"y":5,
		"z":-1
	},
	 {
		"class":7,
		"image":"userdata 00000169B0E52118",
		"occupant":0,
		"open":-1,
		"range":0,
		"x":-3,
		"y":-2,
		"z":5
	},
	 {
		"class":8,
		"image":"userdata 00000169B0E52AB8",
		"occupant":0,
		"open":-1,
		"range":0,
		"x":-3,
		"y":-1,
		"z":4
	},
	 {
		"class":2,
		"image":"userdata 00000169B0E52C08",
		"occupant":0,
		"open":-1,
		"range":0,
		"x":-3,
		"y":0,
		"z":3
	},
	 {
		"class":8,
		"image":"userdata 00000169B0E52AB8",
		"occupant":0,
		"open":-1,
		"range":0,
		"x":-3,
		"y":1,
		"z":2
	},
	 {
		"class":1,
		"image":"userdata 00000169B0E523B8",
		"occupant":0,
		"open":-1,
		"range":0,
		"x":-3,
		"y":2,
		"z":1
	},
	 {
		"class":8,
		"image":"userdata 00000169B0E52188",
		"occupant":0,
		"open":-1,
		"range":0,
		"x":-3,
		"y":3,
		"z":0
	},
	 {
		"class":6,
		"image":"userdata 00000169B0E52F18",
		"occupant":0,
		"open":-1,
		"range":0,
		"x":-3,
		"y":4,
		"z":-1
	},
	 {
		"class":8,
		"image":"userdata 00000169B0E52B98",
		"occupant":0,
		"open":-1,
		"range":0,
		"x":-3,
		"y":5,
		"z":-2
	},
	 {
		"class":4,
		"image":"userdata 00000169B0E52CE8",
		"occupant":0,
		"open":-1,
		"range":0,
		"x":-2,
		"y":-3,
		"z":5
	},
	 {
		"class":4,
		"image":"userdata 00000169B0E52CE8",
		"occupant":0,
		"open":-1,
		"range":0,
		"x":-2,
		"y":-2,
		"z":4
	},
	 {
		"class":1,
		"image":"userdata 00000169B0E52738",
		"occupant":0,
		"open":-1,
		"range":0,
		"x":-2,
		"y":-1,
		"z":3
	},
	 {
		"class":1,
		"image":"userdata 00000169B0E52C78",
		"occupant":0,
		"open":-1,
		"range":0,
		"x":-2,
		"y":0,
		"z":2
	},
	 {
		"class":7,
		"image":"userdata 00000169B0E52D58",
		"occupant":0,
		"open":-1,
		"range":0,
		"x":-2,
		"y":1,
		"z":1
	},
	 {
		"class":7,
		"image":"userdata 00000169B0E527A8",
		"occupant":0,
		"open":-1,
		"range":0,
		"x":-2,
		"y":2,
		"z":0
	},
	 {
		"class":8,
		"image":"userdata 00000169B0E52AB8",
		"occupant":0,
		"open":-1,
		"range":0,
		"x":-2,
		"y":3,
		"z":-1
	},
	 {
		"class":4,
		"image":"userdata 00000169B0E520A8",
		"occupant":0,
		"open":-1,
		"range":0,
		"x":-2,
		"y":4,
		"z":-2
	},
	 {
		"class":4,
		"image":"userdata 00000169B0E525E8",
		"occupant":0,
		"open":-1,
		"range":0,
		"x":-2,
		"y":5,
		"z":-3
	},
	 {
		"class":2,
		"image":"userdata 00000169B0E52658",
		"occupant":0,
		"open":-1,
		"range":0,
		"x":-1,
		"y":-4,
		"z":5
	},
	 {
		"class":3,
		"image":"userdata 00000169B0E52EA8",
		"occupant":0,
		"open":-1,
		"range":0,
		"x":-1,
		"y":-3,
		"z":4
	},
	 {
		"class":8,
		"image":"userdata 00000169B0E52B98",
		"occupant":0,
		"open":-1,
		"range":0,
		"x":-1,
		"y":-2,
		"z":3
	},
	 {
		"class":6,
		"image":"userdata 00000169B0E522D8",
		"occupant":0,
		"open":-1,
		"range":0,
		"x":-1,
		"y":-1,
		"z":2
	},
	 {
		"class":7,
		"image":"userdata 00000169B0E52D58",
		"occupant":0,
		"open":-1,
		"range":0,
		"x":-1,
		"y":0,
		"z":1
	},
	 {
		"class":1,
		"image":"userdata 00000169B0E52C78",
		"occupant":0,
		"open":-1,
		"range":0,
		"x":-1,
		"y":1,
		"z":0
	},
	 {
		"class":1,
		"image":"userdata 00000169B0E523B8",
		"occupant":0,
		"open":-1,
		"range":0,
		"x":-1,
		"y":2,
		"z":-1
	},
	 {
		"class":4,
		"image":"userdata 00000169B0E52CE8",
		"occupant":0,
		"open":-1,
		"range":0,
		"x":-1,
		"y":3,
		"z":-2
	},
	 {
		"class":3,
		"image":"userdata 00000169B0E52EA8",
		"occupant":0,
		"open":-1,
		"range":0,
		"x":-1,
		"y":4,
		"z":-3
	},
	 {
		"class":1,
		"image":"userdata 00000169B0E523B8",
		"occupant":0,
		"open":-1,
		"range":0,
		"x":-1,
		"y":5,
		"z":-4
	},
	 {
		"class":5,
		"image":"userdata 00000169B0E52578",
		"occupant":0,
		"open":-1,
		"range":0,
		"x":0,
		"y":-5,
		"z":5
	},
	 {
		"class":8,
		"image":"userdata 00000169B0E52188",
		"occupant":0,
		"open":-1,
		"range":0,
		"x":0,
		"y":-4,
		"z":4
	},
	 {
		"class":1,
		"image":"userdata 00000169B0E523B8",
		"occupant":0,
		"open":-1,
		"range":0,
		"x":0,
		"y":-3,
		"z":3
	},
	 {
		"class":2,
		"image":"userdata 00000169B0E52A48",
		"occupant":0,
		"open":-1,
		"range":0,
		"x":0,
		"y":-2,
		"z":2
	},
	 {
		"class":8,
		"image":"userdata 00000169B0E52188",
		"occupant":0,
		"open":-1,
		"range":0,
		"x":0,
		"y":-1,
		"z":1
	},
	 {
		"class":7,
		"image":"userdata 00000169B0E52D58",
		"occupant":0,
		"open":-1,
		"range":0,
		"x":0,
		"y":0,
		"z":0
	},
	 {
		"class":2,
		"image":"userdata 00000169B0E52A48",
		"occupant":0,
		"open":-1,
		"range":0,
		"x":0,
		"y":1,
		"z":-1
	},
	 {
		"class":1,
		"image":"userdata 00000169B0E523B8",
		"occupant":0,
		"open":-1,
		"range":0,
		"x":0,
		"y":2,
		"z":-2
	},
	 {
		"class":5,
		"image":"userdata 00000169B0E52348",
		"occupant":0,
		"open":-1,
		"range":0,
		"x":0,
		"y":3,
		"z":-3
	},
	 {
		"class":8,
		"image":"userdata 00000169B0E52B98",
		"occupant":0,
		"open":-1,
		"range":0,
		"x":0,
		"y":4,
		"z":-4
	},
	 {
		"class":4,
		"image":"userdata 00000169B0E525E8",
		"occupant":0,
		"open":-1,
		"range":0,
		"x":0,
		"y":5,
		"z":-5
	},
	 {
		"class":5,
		"image":"userdata 00000169B0E52268",
		"occupant":0,
		"open":-1,
		"range":0,
		"x":1,
		"y":-5,
		"z":4
	},
	 {
		"class":3,
		"image":"userdata 00000169B0E52EA8",
		"occupant":0,
		"open":-1,
		"range":0,
		"x":1,
		"y":-4,
		"z":3
	},
	 {
		"class":7,
		"image":"userdata 00000169B0E52D58",
		"occupant":0,
		"open":-1,
		"range":0,
		"x":1,
		"y":-3,
		"z":2
	},
	 {
		"class":1,
		"image":"userdata 00000169B0E52738",
		"occupant":0,
		"open":-1,
		"range":0,
		"x":1,
		"y":-2,
		"z":1
	},
	 {
		"class":5,
		"image":"userdata 00000169B0E52348",
		"occupant":0,
		"open":-1,
		"range":0,
		"x":1,
		"y":-1,
		"z":0
	},
	 {
		"class":7,
		"image":"userdata 00000169B0E52118",
		"occupant":0,
		"open":-1,
		"range":0,
		"x":1,
		"y":0,
		"z":-1
	},
	 {
		"class":7,
		"image":"userdata 00000169B0E52118",
		"occupant":0,
		"open":-1,
		"range":0,
		"x":1,
		"y":1,
		"z":-2
	},
	 {
		"class":7,
		"image":"userdata 00000169B0E52D58",
		"occupant":0,
		"open":-1,
		"range":0,
		"x":1,
		"y":2,
		"z":-3
	},
	 {
		"class":1,
		"image":"userdata 00000169B0E52738",
		"occupant":0,
		"open":-1,
		"range":0,
		"x":1,
		"y":3,
		"z":-4
	},
	 {
		"class":5,
		"image":"userdata 00000169B0E52578",
		"occupant":0,
		"open":-1,
		"range":0,
		"x":1,
		"y":4,
		"z":-5
	},
	 {
		"class":4,
		"image":"userdata 00000169B0E52CE8",
		"occupant":0,
		"open":-1,
		"range":0,
		"x":2,
		"y":-5,
		"z":3
	},
	 {
		"class":1,
		"image":"userdata 00000169B0E52738",
		"occupant":0,
		"open":-1,
		"range":0,
		"x":2,
		"y":-4,
		"z":2
	},
	 {
		"class":7,
		"image":"userdata 00000169B0E52118",
		"occupant":0,
		"open":-1,
		"range":0,
		"x":2,
		"y":-3,
		"z":1
	},
	 {
		"class":4,
		"image":"userdata 00000169B0E525E8",
		"occupant":0,
		"open":-1,
		"range":0,
		"x":2,
		"y":-2,
		"z":0
	},
	 {
		"class":2,
		"image":"userdata 00000169B0E52658",
		"occupant":0,
		"open":-1,
		"range":0,
		"x":2,
		"y":-1,
		"z":-1
	},
	 {
		"class":7,
		"image":"userdata 00000169B0E527A8",
		"occupant":0,
		"open":-1,
		"range":0,
		"x":2,
		"y":0,
		"z":-2
	},
	 {
		"class":4,
		"image":"userdata 00000169B0E520A8",
		"occupant":0,
		"open":-1,
		"range":0,
		"x":2,
		"y":1,
		"z":-3
	},
	 {
		"class":1,
		"image":"userdata 00000169B0E52738",
		"occupant":0,
		"open":-1,
		"range":0,
		"x":2,
		"y":2,
		"z":-4
	},
	 {
		"class":7,
		"image":"userdata 00000169B0E52D58",
		"occupant":0,
		"open":-1,
		"range":0,
		"x":2,
		"y":3,
		"z":-5
	},
	 {
		"class":6,
		"image":"userdata 00000169B0E526C8",
		"occupant":0,
		"open":-1,
		"range":0,
		"x":3,
		"y":-5,
		"z":2
	},
	 {
		"class":8,
		"image":"userdata 00000169B0E52188",
		"occupant":0,
		"open":-1,
		"range":0,
		"x":3,
		"y":-4,
		"z":1
	},
	 {
		"class":5,
		"image":"userdata 00000169B0E52578",
		"occupant":0,
		"open":-1,
		"range":0,
		"x":3,
		"y":-3,
		"z":0
	},
	 {
		"class":2,
		"image":"userdata 00000169B0E52658",
		"occupant":0,
		"open":-1,
		"range":0,
		"x":3,
		"y":-2,
		"z":-1
	},
	 {
		"class":5,
		"image":"userdata 00000169B0E52348",
		"occupant":0,
		"open":-1,
		"range":0,
		"x":3,
		"y":-1,
		"z":-2
	},
	 {
		"class":2,
		"image":"userdata 00000169B0E52658",
		"occupant":0,
		"open":-1,
		"range":0,
		"x":3,
		"y":0,
		"z":-3
	},
	 {
		"class":5,
		"image":"userdata 00000169B0E52578",
		"occupant":0,
		"open":-1,
		"range":0,
		"x":3,
		"y":1,
		"z":-4
	},
	 {
		"class":1,
		"image":"userdata 00000169B0E52738",
		"occupant":0,
		"open":-1,
		"range":0,
		"x":3,
		"y":2,
		"z":-5
	},
	 {
		"class":6,
		"image":"userdata 00000169B0E52F18",
		"occupant":0,
		"open":-1,
		"range":0,
		"x":4,
		"y":-5,
		"z":1
	},
	 {
		"class":2,
		"image":"userdata 00000169B0E52C08",
		"occupant":0,
		"open":-1,
		"range":0,
		"x":4,
		"y":-4,
		"z":0
	},
	 {
		"class":3,
		"image":"userdata 00000169B0E52498",
		"occupant":0,
		"open":-1,
		"range":0,
		"x":4,
		"y":-3,
		"z":-1
	},
	 {
		"class":1,
		"image":"userdata 00000169B0E52C78",
		"occupant":0,
		"open":-1,
		"range":0,
		"x":4,
		"y":-2,
		"z":-2
	},
	 {
		"class":3,
		"image":"userdata 00000169B0E52428",
		"occupant":0,
		"open":-1,
		"range":0,
		"x":4,
		"y":-1,
		"z":-3
	},
	 {
		"class":8,
		"image":"userdata 00000169B0E52AB8",
		"occupant":0,
		"open":-1,
		"range":0,
		"x":4,
		"y":0,
		"z":-4
	},
	 {
		"class":4,
		"image":"userdata 00000169B0E520A8",
		"occupant":0,
		"open":-1,
		"range":0,
		"x":4,
		"y":1,
		"z":-5
	},
	 {
		"class":7,
		"image":"userdata 00000169B0E52D58",
		"occupant":0,
		"open":-1,
		"range":0,
		"x":5,
		"y":-5,
		"z":0
	},
	 {
		"class":3,
		"image":"userdata 00000169B0E52428",
		"occupant":0,
		"open":-1,
		"range":0,
		"x":5,
		"y":-4,
		"z":-1
	},
	 {
		"class":7,
		"image":"userdata 00000169B0E52118",
		"occupant":0,
		"open":-1,
		"range":0,
		"x":5,
		"y":-3,
		"z":-2
	},
	 {
		"class":6,
		"image":"userdata 00000169B0E526C8",
		"occupant":0,
		"open":-1,
		"range":0,
		"x":5,
		"y":-2,
		"z":-3
	},
	 {
		"class":3,
		"image":"userdata 00000169B0E52428",
		"occupant":0,
		"open":-1,
		"range":0,
		"x":5,
		"y":-1,
		"z":-4
	},
	 {
		"class":7,
		"image":"userdata 00000169B0E52D58",
		"occupant":0,
		"open":-1,
		"range":0,
		"x":5,
		"y":0,
		"z":-5
	}
]
4

I think this is a scope gotcha.

Try:

function fLoadMap(fvMap)
	return playdate.datastore.read(fvMap)
end

rHexList = fLoadMap("testmapsave")
5

Thanks a lot, that worked. But... why? The save function has no problem reading the global table rHexList and making use of it. Why does the load function seem to treat scope differently?

6

It was a given that you were using rHexList outside of the load function, so it was a small jump to think that it was a scope problem.

Why depends on how and where you are declaring your variable and is a bit of a Lua quirk. In your code once the function ends the variable goes back to its previous value (nil).

This is a nice summary:
http://lua-users.org/wiki/ScopeTutorial

Making the function local is also a solution.