When should I access properties with self in swift?

Question

In a simple example like this, I can omit self for referencing backgroundLayer because it's unambiguous which backgroundLayer the backgroundColor is set on.

class SpecialView: UIView {
    let backgroundLayer = CAShapeLayer()

    init() {
        backgroundLayer.backgroundColor = UIColor.greenColor().CGColor
    }
}

But, just like in Objective-C, we can confuse things by adding local variables (or constants) named similarly. Now the backgroundColor is being set on the non-shape layer:

class SpecialView: UIView {
    let backgroundLayer = CAShapeLayer()

    init() {
        var backgroundLayer = CALayer()

        backgroundLayer.backgroundColor = UIColor.greenColor().CGColor
    }
}

(this is resolved by using self.backgroundLayer.backgroundColor)

In Objective-C I always eschewed ivars for properties and properties were always prefixed with self for clarity. I don't have to worry about ivars in swift but are there other considerations for when I should use self in swift?

Answer 1

The only times self is required are when referencing a property inside a closure and, as you pointed out, to differentiate it from a local variable with the same name.

However, personally, I prefer to always write "self" because:

1. That is an instant and obvious sign that the variable is a property. This is important because it being a property means that its state can vary more widely and in different ways than a local variable. Also, changing a property has larger implications than changing a local variable.
2. The code does not need to be updated if you decide to introduce a parameter or variable with the same name as the property
3. Code can be easily copied in and out of closures that do require self