How to use UIView as inverted mask for another UIView?

Applying a UIView as mask to another UIView is no problem.

let view = UIView(...) 
let mask = UIView(...) 
view.mask = mask

Now only those parts of view will be visible where the mask view is also visible. However, how can this be inverted? I would like view to visible where mask is NOT visible. How can I do this?

While I found several solutions to invert paths based masks (using CAShapeLayer) or to invert images, this is not what I am looking for. I do not want to invert a path mask or an image but a view mask.

Assume the view is a red rect and the mask is a green circle. Applying the mask to the view would result in a red circle. However, I would like to create a red rect with a circle hole in it.

Again: Creating a circle path and applying it as mask is no problem. I am NOT looking for path masks (inverted or not) but for a solution to use any UIView as inverted mask.

Is this possible?

This depends a bit on what you mean by "any UIView" and "inverted".

For example... if this is anyView:

What is inverted?

Let's assume that you're talking about a UIView with a clear background, containing some subviews and maybe some shapes, etc.

So, if we setup a label with lots of large text that will be behind our views:

then add an image view that we want to mask, our anyView, and another copy of anyView with clear background so we can see what we're doing:

What we can do is render anyView to a UIImage (renderedImage), then create another UIImage with a solid color (can be any solid color, I used .systemGreen for this example), and then render renderedImage with blendMode: .destinationOut, to get this:

Then we'll create a new UIImageView with that image, and use that as the mask:

func mask(someView: UIView, withView: UIView) {
	
	// make sure the background of the view we're going to use
	//	as the mask is clear
	let bkgColor = withView.backgroundColor
	withView.backgroundColor = .clear
	
	let sz = withView.bounds.size
	
	let renderer = UIGraphicsImageRenderer(size: sz)
	
	let renderedImage = renderer.image { rendererContext in
		withView.drawHierarchy(in: withView.bounds, afterScreenUpdates: true)
	}
	
	let invertedImage = renderer.image { rendererContext in
		UIColor.systemGreen.setFill()
		UIRectFill(.init(origin: .zero, size: renderedImage.size))
		renderedImage.draw(at: .zero, blendMode: .destinationOut, alpha: 1.0)
	}
	
	tempImageView.image = invertedImage
	
	// create a new image view to use as a mask
	let newMaskView = UIImageView(frame: someView.bounds)
	newMaskView.image = invertedImage
	someView.mask = newMaskView
	
	// reset the mask source view's background
	withView.backgroundColor = bkgColor
	
}

giving us this result: