How do I reference an instance variable in lua?

Question

function example()
    help = "no"
end

meme = example()

print(meme.help)

This code throws a run-time error. I don't know what to do.

I'm trying to teach myself lua and I know this can be done in java, but I can't get it working in lua.

You're not returning any value from example(), see my answer. — AStopher
– AStopher, Commented Dec 6, 2014 at 19:27
Key concept: There are two ways to create something new in Lua: evaluating a table constructor {} creates a new table value; evaluation a function definition example = function() end creates a new function value. — Tom Blodget
– Tom Blodget, Commented Dec 7, 2014 at 4:10

AStopher · Accepted Answer · 2014-12-06 19:45:19Z

1

You're not returning in your function.

If the function doesn't return anything example() doesn't have a value, thus you're receiving a nil value error:

enter image description here

Using as the code is being returned, using help.meme will not work. As it is the only variable returned you can simply use this in your use case:

The below code will fix this:

function example()
    help = "no"
end

example()

print(help)

edited Dec 6, 2014 at 19:45

answered Dec 6, 2014 at 19:27

AStopher

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13 Comments

Joseph Fazekas Over a year ago

puu.sh/djCCK/5eb36e5abe.png now it prints nil instead of throwing an error

AStopher Over a year ago

@JosephFazekas I modified the code, it will now return correctly.

Joseph Fazekas Over a year ago

Thanks this helps, but I dont only want the code to print the value. I want to be able to change it as well. @cybermonkey

AStopher Over a year ago

@JosephFazekas You're probably looking for a table or global value. Simply change meme = example() with meme = "[whatever text you want here]".

AStopher Over a year ago

@JosephFazekas Please review my code modification, that will work. I'll also be grateful if you could upvote and mark my accept my answer (click the tick by the question).

|

LorenzoDonati4Ukraine-OnStrike · Accepted Answer · 2014-12-06 20:08:06Z

0

It is not very clear what you are trying to achieve, but from your question it seems that you want to emulate the object-oriented features of Java.

Keep in mind that Lua has no "instance variables" since it has no classes. Lua object oriented approach is uncommon and, unlike Java, is sort of prototype-based object orientation.

A very basic approach to creating an object with instance variables and methods is the following:

-- this is the "instance"
myobject = {}
-- this defines a new "instance variable" named `help`
myobject.help = "this is the help text"

-- this defines a getter method for the instance
-- the special name `self` indicates the instance
function myobject:GetHelp()
    return self.help
end

-- this defines a setter method for the instance
function myobject:SetHelp( help_text )
    self.help = help_text
end

print( myobject:GetHelp() )
myobject:SetHelp( "new help text" )
print( myobject:GetHelp() )

You can discover more about object orientation in Lua browsing the links in Lua WIKI's page about object oriented programming.

edited Dec 6, 2014 at 20:08

answered Dec 6, 2014 at 19:52

LorenzoDonati4Ukraine-OnStrike

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1 Comment

Joseph Fazekas Over a year ago

THANK YOU SO MUCH I didn't even realise

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