Function does not update variable?
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:
local uis = game:GetService("UserInputService")
local players = game:GetService("Players")
local player = players.LocalPlayer
local stances = {
["Water"] = {
[1] = {5, ""},
[2] = {10, ""},
[3] = {15, ""},
[4] = {20, ""},
[5] = {35, ""}
} ,
["Earth"] = {
[1] = {5, ""},
[2] = {10, ""},
[3] = {15, ""},
[4] = {20, ""},
[5] = {35, ""}
} ,
["Fire"] = {
[1] = {5, ""},
[2] = {10, ""},
[3] = {15, ""},
[4] = {20, ""},
[5] = {35, ""}
} ,
["Air"] = {
[1] = {5, ""},
[2] = {10, ""},
[3] = {15, ""},
[4] = {20, ""},
[5] = {35, ""}
} ,
}
local key = "T"
function setStance(Element, Stance)
if stances[Element] then
local rng = math.random(1, 5)
if stances[Element][rng][1] then
Stance = stances[Element][rng][1]
return true
else
return false
end
else
return false
end
end
uis.InputBegan:connect(function(input, gameProcessedEvent)
if input.KeyCode.Name == key and not gameProcessedEvent then
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
local stance
if setStance(plrElement, stance) then
print(stance)
else
print("Error")
end
end
end)
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!
2 answers
Your Problem
local stance setStance(plrElement, stance)
What you are trying to do is set the variable stance by passing it into this function. This is fine and dandy and will work as you expect when the variable is passed in by reference, but not when it is passed by value.
"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:
function setStance(Element)
if stances[Element] then
local rng = math.random(1, 5)
if stances[Element][rng][1] then
return stances[Element][rng][1]
else
return nil
end
else
return nil
end
end
uis.InputBegan:connect(function(input, gameProcessedEvent)
if input.KeyCode.Name == key and not gameProcessedEvent then
local plrElement = player:FindFirstChild("Element").Value
local stance = setStance(plrElement)
if stance then
print(stance)
else
print("Error")
end
end
end)
You're passing it by value, and not by reference. Passing by value, you're just making a copy and not really changing it, which means the original variable wasn't modified.