Question about metatables/metamethods, multiple inheritance?
So I'm messing around with metatable's, i understand how setmetatable and __index and __newindex works, but i don't understand inheritance and multiple inheritance yet quite well.
My Problem: I try to get the variable 'h' but it prints nil, everything else is fine, what am i doing wrong here? How can i have nested metatables connected to each other, like fallback when one fails it goes to other.
Here's Code:
local Window = {
ClassName = 'ScrollingFrame',
Size = UDim2.new(0,0,0,0),
CursorColor3 = Color3.fromRGB(255,255,255),
}
Window.__index = Window
Window.metatable = {}
Window.metatable.__index = {
getClassName = function(self)
return self.ClassName
end
}
setmetatable(Window, Window.metatable)
--I Can't to seem to get "h" variable from here for some reason?,Why?
Window.LockedProperties = {}
Window.LockedProperties.__index = {h = 999}
setmetatable(Window.metatable, Window.LockedProperties)
--Constructor
function Window.new()
return setmetatable({},Window)
end
local w = Window.new()
print(w.Size)
print(w.h)
print(w:getClassName())
1 answer
I believe you went about it wrong.
As far as I know, the __index metamethod is supposed to be a function, not a table, which I believe is the main error.
-->> VALUES
local Window = {Size = UDim2.new(0,0,0,0),ClassName = "ScrollingFrame"}
Window.LockedProperties = {h = 999}
Window.__index = Window
-->> FUNCTIONS
Window.Metatable = { -->> one table for everything, no need for heaps
__index = function(table,index)
return table.LockedProperties[index]
end
-->> you should also use the other function that fires when a value gets set to prevent the locked properties from being changed
}
Window.LockedProperties.__newindex = function(table,index,value)
warn("Cannot set new value to LockedProperties")
end
setmetatable(Window.LockedProperties,Window.LockedProperties)
setmetatable(Window,Window.Metatable)
function Window.new()
return setmetatable({},Window)
end
function Window:GetClassName(self)
return self.ClassName
end
-->> TESTING
local w = Window.new()
print(w.Size,w.h) -->> it should print: 0,0,0,0 999
To explain:
You would want to set everything first so that you know what is where. I like to organise my code when it gets long or complicated - it's very useful.
Next, I create the metatable, and make the __index function that returns the locked property (that's literally it all it needs to do). After that, I simply set the metatable, then create the other functions and methods.
Note that when setting a function inside a table, it will by default be indexed by . and not :. The latter can only be indexed when you set it like I did.
EDITS:
So I tried to come up with a read-only system, but I got stumped. __newindex only fires when a new value and index are created, not when a value is changed.
My only other idea is to move the LockedProperties upon creation into a different entity, and index using the table's ID (tostring(table)).
But I don't have time to work on that, so good luck ;)
Please comment any problems/questions you have. Hope I helped!
~TDP
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