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 t

Answer 1

If you work with classes then, as you say, you can modify the class because the parameter is a reference to the class. But this won't work when your parameter is a value type (https://docs.swift.org/swift-book/LanguageGuide/Functions.html - In-Out Parameters Section)

One good example of using inout is this one (defining math for CGPoints):

func + (left: CGPoint, right: CGPoint) -> CGPoint {
  return CGPoint(x: left.x + right.x, y: left.y + right.y)
}

func += (left: inout CGPoint, right: CGPoint) {
  left = left + right
}