In Objective-C such line
self.mainImageView.layer.cornerRadius = CGRectGetWidth(self.mainImageView.frame)/4.0f;
does its job, I tried it in Swift using analogy
self.mainImageView.layer.cornerRadius = CGRectGetWidth(self.mainImageView.frame)/4.0
and it doesn't change anything, the corners are the same as before. Moreover, Xcode does not show any syntax errors. Does Swift support any other way to reach this goal? I checked some other threads here and usually it's getting done in Swift in the way showed above.
Layer draws out of clip region, you need to set it to mask to bounds:
self.mainImageView.layer.masksToBounds = true
From the docs:
By default, the corner radius does not apply to the image in the layer’s contents property; it applies only to the background color and border of the layer. However, setting the masksToBounds property to true causes the content to be clipped to the rounded corners