Beginner question, I realise that when the Xcode declares a function for @IBAction, it declares it as below:
@IBAction func hardnessSelected(_ sender: UIButton),
which I read is,
Create a function called hardness selected which accepts a parameter called sender which accepts the type UI button.
From my understanding so far _ is used when you want to declare a variable that you are not going to mutate e.g. in a for loop to tell swift the value of this variable doesn't matter to optimize performance.
However, in the above case there is a name for the variable "sender" as well as _ which I don't understand why.
Can someone please explain?
This place is declared for the label which means that once you call the function it won't appear to you for example:
func sum (_ number1: Int, _ number2: Int) {
print(number1 + number2)
}
once you call the function you won't need to mention number1 or number2 but you will only write the number directly :
sum(1, 2)
To be clear it's the same as using the function below:
func summation(myFirstNumber number1: Int, mySecondNumber number2: Int) {
print (number1 + number2)
}
but here instead of using _ I've used a label so when I called the function, I will use these labels :
summation(myFirstNumber: 1, mySecondNumber: 2)
So it's clear now that _ is instead of writing a label.
For more information check: Function Argument Labels and Parameter Names from here