Function does not update variable?

Asked by

8 years ago

Hi!

I have a function that takes two arguments, a StringValue object and a variable that is set to update with my desired result. My issue is with the updating of the second argument.

I've used print() to determine that I'm indexing the correct value and yet I still can't get the result I've want, so I've deduced that either this is impossible or I'm making a major mistake.

Here is my code:

01local uis = game:GetService("UserInputService")
02local players = game:GetService("Players")
03local player = players.LocalPlayer
04 
05local stances = {
06    ["Water"] = {
07        [1] = {5, ""},
08        [2] = {10, ""},
09        [3] = {15, ""},
10        [4] = {20, ""},
11        [5] = {35, ""}
12    } ,
13 
14    ["Earth"] = {
15        [1] = {5, ""},
16        [2] = {10, ""},
17        [3] = {15, ""},
18        [4] = {20, ""},
19        [5] = {35, ""}
20    } ,
21 
22    ["Fire"] = {
23        [1] = {5, ""},
24        [2] = {10, ""},
25        [3] = {15, ""},
26        [4] = {20, ""},
27        [5] = {35, ""}
28    } ,
29 
30    ["Air"] = {
31        [1] = {5, ""},
32        [2] = {10, ""},
33        [3] = {15, ""},
34        [4] = {20, ""},
35        [5] = {35, ""}
36    } , 
37}
38 
39local key = "T"
40 
41function setStance(Element, Stance)
42    if stances[Element] then   
43        local rng = math.random(1, 5)
44 
45        if stances[Element][rng][1] then
46            Stance = stances[Element][rng][1]  
47            return true
48        else
49            return false   
50        end
51    else
52        return false   
53    end
54end
55 
56uis.InputBegan:connect(function(input, gameProcessedEvent)
57    if input.KeyCode.Name == key and not gameProcessedEvent then
58        local plrElement = player:FindFirstChild("Element").Value --I've set this value to Fire, this isn't the issue. I've already used print() to figure out that it isn't an issue with my values
59        local stance
60        if setStance(plrElement, stance) then
61            print(stance)
62        else
63            print("Error")  
64        end
65    end
66end)
 View all 66 lines...

To clarify more, declaring a variable with no value will set the variable's value to nil, and upon printing stance after confirming that it has updated in the function, I get nil.

This is really stumping me. If I could get a reason why this is happening it'd be very appreciated. Thanks!

"Passing by Reference" vs "Passing by Value"

When you pass in an argument by reference, the parameter of the function then points to the same memory address as the argument you passed in. This means that when you make changes to the parameter inside the function, you also make changes to the variable outside the function.

However, when you pass in a variable by value it copies the data from your variable and assigns it to the parameter, giving it a different memory address. When you make changes to the parameter inside the function, the changes are not made to your variable you passed i in as it points to a different set of memory.

In Lua, we can not control how our variables work. There are default ways that each type of object act when you pass them into functions:

By Reference: tables, functions, threads, and userdata values

By Value: nil, boolean, number, string

Solution

Since your variable is nil, we are going to need to change the way that you function works. We need to return back the stance we want and to assign to the variable:

01function setStance(Element)
02    if stances[Element] then
03        local rng = math.random(1, 5)
04 
05        if stances[Element][rng][1] then
06            return stances[Element][rng][1]
07        else
08            return nil
09        end
10    else
11        return nil
12    end
13end
14 
15uis.InputBegan:connect(function(input, gameProcessedEvent)
16    if input.KeyCode.Name == key and not gameProcessedEvent then
17        local plrElement = player:FindFirstChild("Element").Value
18        local stance = setStance(plrElement)
19 
20        if stance then
21            print(stance)
22        else
23            print("Error")  
24        end
25    end
26end)
 View all 26 lines...

Function does not update variable?

2 answers

Your Problem

"Passing by Reference" vs "Passing by Value"

Solution

Answer this question