✓ ANSWER ACCEPTED

How to use the keyword `self` in lua?

Asked Jul 20, 201916,057 views3 answers

so i've been ticking with the self keyword in lua, I am assuming that the self keyword works very much like the this keyword in javascript, but i guess i could be wrong, since whenever I try to index a value from it, lua throws an error tha's like this

attempt to index global 'self' (a nil value)

and here is my code;

local account = {
	name ="Roblox",
	sonsName = self.name.." jr", --error?

	get = function()
		return self.name  --error?
	end

}


print(account.get())

I tried making a closure to see if it'll get rid of the global part in the error, but it's no use:

here is the code


local account = (function()
	local account = {
		name ="Roblox",
		sonsName = self.name.." jr", --attempt to index 'self' a nil value

		get = function()
			return self.name --attempt to index 'self' a nil value
		end

	}

	return account
end)()


print(account.get())

AnonymousJul 20, 2019Edited Jul 20, 2019

3 answers

✓ Accepted answer

It is important to clarify that self is not a keyword, but a variable. The reason why quite a vast number of people tend to make this error is because ROBLOX highlights self as a keyword. This is incorrect.

Now to answer your question, we use self as a way to access the previous argument called in the function, without passing the argument explicitly. self is notably used in Object Oriented Programming Implementation in Lua. Consider the following example.

local t = {
    message = "";
}

function t.set_message (self, message)
    print(t);
    t.message = message;
    print(message);
end

t.set_message (t, "Hello World");
t:set_message ("Hello World");

Notice how when I used : (colon) symbol, I did not pass the table t as an argument.

Let me help you out with your example now. Consider using getters and setters

-- [Declaration Section]
local account = {
    name = "";
};

-- [Procedure Section]
function account.set_name (self, name)
    self.name = name;
end

function account.get_name (self)
   return self.name; 
end

-- [Output Section]
account:set_name("Zafirua");
print(account:get_name());

For in depth detail on why exactly we use it and its purposes, please consider reading the ROBLOX Dev wiki or Lua Reference Manual 5.1 +

AnonymousJul 20, 2019Edited Jul 20, 2019Permalink

2 comments

ohhhhh, so calling a method on a constructor with the colon operator automatically passes the factory of that method as first argument to the method right?

AnonymousJul 20, 2019#

btw, i am not in roblox.. i am running the code in command line..

AnonymousJul 20, 2019#

In addition to the fact that self is implicitly passed to a function when using the colon syntax (i.e. account:get_name()), it's worth noting that self can also be implicitly received as a function argument using a similar syntax. I'll build upon Zafirua's excellent answer to provide an example here:

local account = {
	name = "";
};

-- [snip]

-- This declaration is equivalent to the original
function account:get_name()
	return self.name;
end

In programming terminology, we call this "syntactic sugar".

AnonymousJul 20, 2019Edited Dec 8, 2021Permalink

3 comments

sweet.. thanks for clarifying :D

AnonymousJul 20, 2019#

in your code example, line 08 should be just function account:get_name(), with no explicit parameters, right?

AnonymousAug 19, 2021#

@xiq23: Thank you, I've corrected my answer!

AnonymousDec 8, 2021#

hmm.... try

local account = {
    name ="Roblox",
    sonsName = self.name.." jr", --error?

    get = function()
        return account.name
    end

}


print(account.get())

AnonymousJul 20, 2019Permalink

1 comment

well, I know i can do that, but the self keyword would be useful in case the account variable name was changed

AnonymousJul 20, 2019#

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