swift - When to use inout parameters?

Question

When passing a class or primitive type into a function, any change made in the function to the parameter will be reflected outside of the class. This is basically the same thing an inout parameter is supposed to do.

What is a good use case for an inout parameter?

Answer 1

inout means that modifying the local variable will also modify the passed-in parameters. Without it, the passed-in parameters will remain the same value. Trying to think of reference type when you are using inout and value type without using it.

For example:

import UIKit

var num1: Int = 1
var char1: Character = "a"

func changeNumber(var num: Int) {
    num = 2
    print(num) // 2
    print(num1) // 1
}
changeNumber(num1)

func changeChar(inout char: Character) {
    char = "b"
    print(char) // b
    print(char1) // b
}
changeChar(&char1)

A good use case will be swap function that it will modify the passed-in parameters.

Swift 3+ Note: Starting in Swift 3, the inout keyword must come after the colon and before the type. For example, Swift 3+ now requires func changeChar(char: inout Character).