Overriding CALayer's initWithLayer in Swift

Question

I'm learning how to use CALayers and perform animations on their properties. To a beginner Apple's documentation is simply cryptic. I managed to find an example (called: CustomAnimatableProperty) in iOS's documentation which somewhat 'explains' how to do what I want:

// For CALayer subclasses, always support initWithLayer: by copying over custom properties.
-(id)initWithLayer:(id)layer {
    if( ( self = [super initWithLayer:layer] ) ) {
        if ([layer isKindOfClass:[BulbLayer class]]) {
            self.brightness = ((BulbLayer*)layer).brightness;
        }
    }
    return self;
}

Translating the method override to Swift however gives me a few errors:

The errors stem from my lacking understanding of what's going on here. I'm not sure what are we checking for in those nested if statements. Also I am a bit baffled by the usage of "=" in the main if(){} block. Shouldn't we be checking ("==") for equality?

But yeah any general help would mean the world. I've tried reviewing a few blog-posts / tutorials online, however non of them deals with this speciffic issue.

Answer 1

The self = [super init...] idiom is for Objective-C, not Swift. In Swift, init blocks aren't normal functions and don't return anything.

While we're at it, let's use the Swift idiom for downcasting. We also need to guarantee that size is initialized before we call super.init.

override init(layer: AnyObject!) {
    if let layer = layer as? SegmentActiveLayer {
        size = layer.size
    } else {
        size = 0
    }
    super.init(layer: layer)
}