Auto-updating table

[Zista]

Are there any metamethods you can add to a table that will make it automatically update?

I have a table with all of the values being set to values from my SavedVariables. Is there any way to update the table automatically when the one of the SavedVariables gets changed?

I am looking for something similar to the way AceDB manages the db variables for each file in the addon (even though you are updating the local variable "db" it still updates the SavedVariables).

[ravagernl]

You could use the metamethod __newindex, iirc

[Zista]

Would that work if you had a table like:

local myTable = {
	a = db.a
	b = db.b
	c = db.c
}

where if you changed the value of db.a, myTable.a would change as well?

[Akkorian]

Hi Zista,

Unless you’re doing something really weird, why don’t you read directly from your saved variables table?

If you really want to keep two separate tables, you could set a metatable with a “__newindex” method on your saved variables table:

setmetatable( MySavedVar, {
    __newindex = function( tbl, key, value )
        MySavedVar[ key ] = value
        myTable[ key ] = value
    end
} )
 
MySavedVar[ "foo" ] = "bar"
 
print( myTable[ "foo" ] )
==> "bar"

Or, you could write the value in both tables instead of only in one:

function SetNewValue( key, value )
    MySavedVar[ key ] = value
    myTable[ key ] = value
end
 
SetNewValue( "foo", "bar" )
 
print( myTable[ "foo" ] )
==> "bar"

Or, you could set up your second table like this, storing just the key name:

local myTable = {
    a = "foo",
}
 
print( MySavedVar[ myTable.a ] )
==> "bar"

[SDPhantom]

Some added information, the __newindex metamethod is only run if the table key doesn't exist already (or is nil). Also it's a good practice to avoid the standard value set "table[key]=value" on the same table the metamethod is running from. This may cause the metamethod to trigger recursively and send the scripting engine into an endless loop. To prevent this, use the rawset() function. This function exists specifically to bypass the triggering of metamethods.

Bad code:

local table=setmetatable({},{
	__newindex=function(t,k,v)
		t[k]=v;--	Causes recursive calling
	end;
});

Good code:

local table=setmetatable({},{
	__newindex=function(t,k,v)
		rawset(t,k,v);--	Bypasses metamethods and sets v directly in k of table t
	end;
});

Note: These are just examples, Lua already does this by default only if the metamethod doesn't exist. You still need to set the value yourself if you want to define this metamethod.

[Ailae]

What's the difference between __index and __newindex? On a quick glance they seem to do the same thing, run when a requested table key is nil.

[ravagernl]

Originally Posted by Ailae What's the difference between __index and __newindex? On a quick glance they seem to do the same thing, run when a requested table key is nil.

__index is called when you are trying to get a table index that doesn't exist. (http://www.lua.org/pil/13.4.1.html)
__newindex is called when you are setting a table index that didn't previously exist.(http://www.lua.org/pil/13.4.2.html)

So if you want to track when a table is updated, you can view a solution for that here: http://www.lua.org/pil/13.4.4.html.

May I suggest you look at tekkub's AddOnTemplate Zista, since I'm not sure if you really need this advanced stuff. He has an elegant soltuion imho.

[Zista]

I'm using oUF and have 2 separate addons. In the oUF style addon, I have a table of colors that is made up of values from the SavedVariables from the main addon. I am trying to make it so when one the the colors is changed in the options menu of the main addon, the color table gets updated in the oUF style addon. I have about 60 colors and would like to keep the code condensed as much as possible so I don't want to have each option in the main addon update both the SavedVariable and the oUF color table. I would rather have the oUF color table update automatically so that when the color table is called from it returns the current value of the SavedVariable instead of the value that the SavedVariable was when the color table was initialized.

My table currently looks like this:

local db = MyAddon.db.profile
local colors = setmetatable({
	power = setmetatable({
		["MANA"] = {tonumber(db.oUF.Colors.Power.Mana.r), tonumber(db.oUF.Colors.Power.Mana.g), tonumber(db.oUF.Colors.Power.Mana.b)},
		["RAGE"] = {tonumber(db.oUF.Colors.Power.Rage.r), tonumber(db.oUF.Colors.Power.Rage.g), tonumber(db.oUF.Colors.Power.Rage.b)},
		["FOCUS"] = {tonumber(db.oUF.Colors.Power.Focus.r), tonumber(db.oUF.Colors.Power.Focus.g), tonumber(db.oUF.Colors.Power.Focus.b)},
		["ENERGY"] = {tonumber(db.oUF.Colors.Power.Energy.r), tonumber(db.oUF.Colors.Power.Energy.g), tonumber(db.oUF.Colors.Power.Energy.b)},
		["RUNES"] = {tonumber(db.oUF.Colors.Power.Runes.r), tonumber(db.oUF.Colors.Power.Runes.g), tonumber(db.oUF.Colors.Power.Runes.b)},
		["RUNIC_POWER"] = {tonumber(db.oUF.Colors.Power.RunicPower.r), tonumber(db.oUF.Colors.Power.RunicPower.g), tonumber(db.oUF.Colors.Power.RunicPower.b)},
		["AMMOSLOT"] = {tonumber(db.oUF.Colors.Power.AmmoSlot.r), tonumber(db.oUF.Colors.Power.AmmoSlot.g), tonumber(db.oUF.Colors.Power.AmmoSlot.b)},
		["FUEL"] = {tonumber(db.oUF.Colors.Power.Fuel.r), tonumber(db.oUF.Colors.Power.Fuel.g), tonumber(db.oUF.Colors.Power.Fuel.b)},
		["POWER_TYPE_STEAM"] = {0.55, 0.57, 0.61},
		["POWER_TYPE_PYRITE"] = {0.60, 0.09, 0.17},
	}, {__index = oUF.colors.power}),
	class = setmetatable({
		["WARRIOR"] = {tonumber(db.oUF.Colors.Class.Warrior.r), tonumber(db.oUF.Colors.Class.Warrior.g), tonumber(db.oUF.Colors.Class.Warrior.b)},
		["PRIEST"] = {tonumber(db.oUF.Colors.Class.Priest.r), tonumber(db.oUF.Colors.Class.Priest.g), tonumber(db.oUF.Colors.Class.Priest.b)},
		["DRUID"] = {tonumber(db.oUF.Colors.Class.Druid.r), tonumber(db.oUF.Colors.Class.Druid.g), tonumber(db.oUF.Colors.Class.Druid.b)},
		["HUNTER"] = {tonumber(db.oUF.Colors.Class.Hunter.r), tonumber(db.oUF.Colors.Class.Hunter.g), tonumber(db.oUF.Colors.Class.Hunter.b)},
		["MAGE"] = {tonumber(db.oUF.Colors.Class.Mage.r), tonumber(db.oUF.Colors.Class.Mage.g), tonumber(db.oUF.Colors.Class.Mage.b)},
		["PALADIN"] = {tonumber(db.oUF.Colors.Class.Paladin.r), tonumber(db.oUF.Colors.Class.Paladin.g), tonumber(db.oUF.Colors.Class.Paladin.b)},
		["SHAMAN"] = {tonumber(db.oUF.Colors.Class.Shaman.r), tonumber(db.oUF.Colors.Class.Shaman.g), tonumber(db.oUF.Colors.Class.Shaman.b)},
		["WARLOCK"] = {tonumber(db.oUF.Colors.Class.Warlock.r), tonumber(db.oUF.Colors.Class.Warlock.g), tonumber(db.oUF.Colors.Class.Warlock.b)},
		["ROGUE"] = {tonumber(db.oUF.Colors.Class.Rogue.r), tonumber(db.oUF.Colors.Class.Rogue.g), tonumber(db.oUF.Colors.Class.Rogue.b)},
		["DEATHKNIGHT"] = {tonumber(db.oUF.Colors.Class.DeathKnight.r), tonumber(db.oUF.Colors.Class.DeathKnight.g), tonumber(db.oUF.Colors.Class.DeathKnight.b)},
	}, {__index = oUF.colors.class}),
	happiness = setmetatable({
		[1] = {tonumber(db.oUF.Colors.Happiness.Happiness1.r), tonumber(db.oUF.Colors.Happiness.Happiness1.g), tonumber(db.oUF.Colors.Happiness.Happiness1.b)},
		[2] = {tonumber(db.oUF.Colors.Happiness.Happiness2.r), tonumber(db.oUF.Colors.Happiness.Happiness2.g), tonumber(db.oUF.Colors.Happiness.Happiness2.b)},
		[3] = {tonumber(db.oUF.Colors.Happiness.Happiness3.r), tonumber(db.oUF.Colors.Happiness.Happiness3.g), tonumber(db.oUF.Colors.Happiness.Happiness3.b)},
	}, {__index = oUF.colors.happiness}),
	runes = setmetatable({
		[1] = {tonumber(db.oUF.Colors.Runes.Rune1.r), tonumber(db.oUF.Colors.Runes.Rune1.g), tonumber(db.oUF.Colors.Runes.Rune1.b)},
		[2] = {tonumber(db.oUF.Colors.Runes.Rune2.r), tonumber(db.oUF.Colors.Runes.Rune2.g), tonumber(db.oUF.Colors.Runes.Rune2.b)},
		[3] = {tonumber(db.oUF.Colors.Runes.Rune3.r), tonumber(db.oUF.Colors.Runes.Rune3.g), tonumber(db.oUF.Colors.Runes.Rune3.b)},
		[4] = {tonumber(db.oUF.Colors.Runes.Rune4.r), tonumber(db.oUF.Colors.Runes.Rune4.g), tonumber(db.oUF.Colors.Runes.Rune4.b)},
	}, {__index = oUF.colors.runes}),
	totembar = setmetatable({
		[1] = {tonumber(db.oUF.Colors.Totems.Fire.r), tonumber(db.oUF.Colors.Totems.Fire.g), tonumber(db.oUF.Colors.Totems.Fire.b)},
		[2] = {tonumber(db.oUF.Colors.Totems.Earth.r), tonumber(db.oUF.Colors.Totems.Earth.g), tonumber(db.oUF.Colors.Totems.Earth.b)},		
		[3] = {tonumber(db.oUF.Colors.Totems.Water.r), tonumber(db.oUF.Colors.Totems.Water.g), tonumber(db.oUF.Colors.Totems.Water.b)},
		[4] = {tonumber(db.oUF.Colors.Totems.Air.r), tonumber(db.oUF.Colors.Totems.Air.g), tonumber(db.oUF.Colors.Totems.Air.b)},	
	}, {__index = oUF.colors.totembar}),
}, {__index = oUF.colors})

At some point I will go back through and change the colors to be unpackable instead of having separate r, g, and b values

[Zista]

Solved it.

I used the __index metamethod to return the value from the SavedVariables and just left the table more or less blank.

EX:

local db = MyAddon.db.profile
local colors = setmetatable({
	power = setmetatable({
	}, {
		__index = function(t, k)
			local color = db.oUF.Colors.Power[k]
			return color and {tonumber(color.r), tonumber(color.g), tonumber(color.b)} or oUF.colors.power[k]
		end
	})
}, {__index = db.oUF.Colors or oUF.colors})