Swift equivalent to __attribute((objc_requires_super))?

Question

Is there a Swift equivalent to

__attribute((objc_requires_super))

which gives a warning if a method doesn't call it's super method?

Basically, I want to warn (or even better, throw a compiler error) if an overridden method doesn't call its super method.

Answer 1

No, there is no Swift equivalent to __attribute((objc_requires_super)).

The equivalent feature, Swift Attributes, contains no such attribute.

The section of the Swift inheritance documentation where such a feature would be mentioned says only:

When you provide a method, property, or subscript override for a subclass, it is sometimes useful to use the existing superclass implementation as part of your override.

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Note that you can prevent overriding functions using final, so you could effectively accomplish what you want by providing empty overridable methods that are called by non-overridable methods:

class AbstractStarship {
    var tractorBeamOn = false

    final func enableTractorBeam() {
        tractorBeamOn = true

        println("tractor beam successfully enabled")

        tractorBeamDidEnable()
    }

    func tractorBeamDidEnable() {
        // Empty default implementation
    }
}

class FancyStarship : AbstractStarship {
    var enableDiscoBall = false

    override func tractorBeamDidEnable() {
        super.tractorBeamDidEnable() // this line is irrelevant

        enableDiscoBall = true
    }
}

Subclasses would then override the overridable methods, and it wouldn't matter whether they called super or not since the superclass's implementation is empty.

As Bryan Chen notes in the comments, this breaks down if the subclass is subclassed.

I make no claims to whether this approach is stylistically good, but it is certainly possible.