Array of functions don't keep their values from their creation - swift

Question

I try to manage my functions with a Manger. The problem is that the function code updates and is not saved in the moment when i add the function to my manager. I try to explain my problem with this example:
class QueueManager {
typealias FunctionType = () -> ()
private var functions = [(String, FunctionType)]()
func add(funcName: String, function: FunctionType) -> QueueManager {
functions.append(funcName, function)
return self
}
func runFirst() -> Bool {
guard functions.isEmpty == false else { return false }
functions.first!.1()
functions.removeFirst()
return true
}
}
Then i do this:
let queueManager = QueueManger()
var value = 1
queueManager.add("simpleFunction"){
print(value)
}
value = 2
queueManager.add("simpleFunction"){
print(value)
}
queueManager.runFist()
queueManager.runFist()
And the result is:
2 // Because value is 2 in both functions. But i added the function while value was 1??
2
But i want the result:
1
2
What am i doing wrong? Thanks in advance!
EDIT: Very easy playground example:
import UIKit
var str = "1"
func go() {
print(str)
}
var array:[()->()] = []
array.append(go)
str = "2"
array.append(go)
array[0]()
array[1]()
// Output:
// 2
// 2
EDIT 2:
I know that 2 2 is the right output for my code. But i want to keep the function in the state of its creation. Is this somehow possible?
EDIT 3:
Thanks for all of your help. But i think i`m failing to explain my problem enough to get suiting answers. I want to call a function with its parameters at a later time. I don't want to keep the reference to the parameter values. I just need to call the function with those parameter values.

Answer 1

In order to understand what happens here lets take a look step-by-step :
Assign 1 to value
Add the print instruction to QueueManager
Assign 2 to value
Add the print instruction to QueueManager
Run the functions using runFirst()
When you add the print(value) instruction you pass value as reference type. This creates a strong reference between variable functions and value. Hence when you actually execute those instructions, using runFirst() it then uses the value stored in value at that point of time.
Let's explore using this example:
var value = 5
queueManager.add(funcName: "simpleFunction"){
print(value)
}
queueManager.add(funcName: "simpleFunction"){
print(value)
}
queueManager.runFirst()
queueManager.runFirst()
value = 10
// output is 5 5
In this case we perform runFirst() first and then update the value. Hence the output is 5 5.
TL;DR - Pass By Reference causes function to print the current value of variable value.
EDIT : Bind the data to the function in QueueManager, this will make sure that the current value of data (during function definition) is associated with the function.
class QueueManager {
typealias FunctionType = (Int) -> ()
private var functions = [(String, FunctionType, Int)]()
func add(funcName: String, function: #escaping FunctionType, data: Int) -> QueueManager
{
functions.append((funcName, function, data))
return self
}
func runFirst() -> Bool
{
guard functions.isEmpty == false else { return false }
functions.first!.1(functions.first!.2)
functions.removeFirst()
return true
}
}
let queueManager = QueueManager()
// define you function within this closure
let functionClosure: (Int) -> () = { (data) in
print(data)
}
var value = 1
queueManager.add(funcName: "simpleFunction", function: functionClosure, data: value)
value = 2
queueManager.add(funcName: "simpleFunction", function: functionClosure, data: value)
queueManager.runFirst()
queueManager.runFirst()
OUTPUT :
1
2

Answer 2

Based on your code, obviously the result should be:
2
2
because you are calling queueManager.runFirst() tow times after editing value = 2
Also, if add function should includes functions.append((funcName, function)) then I assume that its function parameter should be #escaping as follows:
class QueueManager {
typealias FunctionType = () -> ()
private var functions = [(String, FunctionType)]()
func add(funcName: String, function: #escaping FunctionType) -> QueueManager {
functions.append((funcName, function))
return self
}
func runFirst() -> Bool {
guard functions.isEmpty == false else { return false }
functions.first!.1()
functions.removeFirst()
return true
}
}
Thus the output of:
let queueManager = QueueManager()
var value = 1
queueManager.add(funcName: "simpleFunction") {
print(value)
}
queueManager.runFirst()
value = 2
queueManager.add(funcName: "simpleFunction"){
print(value)
}
queueManager.runFirst()
should be:
1
2
because -simply- I called queueManager.runFirst() before calling value = 2
The same issue is applicable to your simple example:
var str = "1"
func go() {
print(str)
}
var array:[()->()] = []
array.append(go)
array[0]()
str = "2"
array.append(go)
array[1]()
calling array.append(go) won't leads to execute go(), you should call it by array[0](); Since you are trying to print the value of the same variable (str) it will always prints the latest value for it. If you want to save each value separately for each function, you should -somehow- declare more than one variable (value or str).

Answer 3

import UIKit
var str = "Hello, playground"
class QueueManager {
typealias FunctionType = () -> ()
private var functions = [(String, FunctionType)]()
func add(funcName: String, function: #escaping FunctionType) -> QueueManager {
functions.append((funcName, function))
return self
}
func runFirst() -> Bool {
guard functions.isEmpty == false else { return false }
print(functions)
functions.first!.1()
functions.removeFirst()
return true
}
}
var value = 1
let queueManager = QueueManager()
func simpleFunction(_ value: AnyObject){
print(value)
}
queueManager.add(funcName: "simpleFunction"){
simpleFunction(value as AnyObject)
}
queueManager.add(funcName: "simpleFunction"){
value = 2
simpleFunction(value as AnyObject)
}
queueManager.runFirst()
queueManager.runFirst()
You have to update your value after the first simpleFunction was added.
Playground Output:
[("simpleFunction", (Function)), ("simpleFunction", (Function))]
1
[("simpleFunction", (Function))]
2