[swift-users] FlatMap and Casting

[Dennis Weissmann]

Since sublayers are optional you’re calling the the flatMap function on Optionals, which behaves differently.

let layers = myView.layer.sublayers?.flatMap({ $0 as? CAShapeLayer })		// sublayers?. instead of sublayers.

should fix the problem :)

- Dennis

> On Apr 21, 2016, at 9:53 PM, Nate Birkholz via swift-users <swift-users at swift.org> wrote:
> 
> myView.layer.sublayers returns an array of CALayer objects. Some of my sublayers are CAShapeLayers. I want to act on the CAShapeLayer objects.
> 
> Shouldn't flatMap allow me to conditionally cast CALayers to CAShapeLayers? i.e. 
> let layers = myView.layer.sublayers.flatMap({ $0 as? CAShapeLayer })
> 
> The compiler warns "Cast from '[CALayer]' to unrelated type 'CAShapeLayer' always fails"
> 
> So it looks like $0 is the array itself. 
> 
> This works: 
> let layers = myView.layer.sublayers?.filter({ $0 is CAShapeLayer }).map({ $0 as? CAShapeLayer }) 
> 
> But I thought FlatMap should do it in a single step.
> 
> -- 
> Nate Birkholz
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