How to do I initialise Swift array of object eg. CALayer

Question

I was able to initialise CALayer using method 1 which is properly working in the rest of code but not method 2. Could you please advise the what is wrong.

Initialise CALayer

var layers:[CALayer]!

Method 1. is working

layers = [CALayer(), CALayer(), CALayer(), CALayer(), CALayer(), CALayer(), CALayer(), CALayer()]

Method 2. is not working

layers = [CALayer](count: 8, repeatedValue: CALayer())

Answer 1

You can use map and an interval:

layers = (0..<8).map { _ in CALayer() }

The _ in is an annoyance that shouldn’t be necessary but Swift’s type inference currently needs it.

The map approach has a big advantage over a for-based approach, since it means you can declare layers with let if it isn’t going to need to change further later:

let layers = (0..<8).map { _ in CALayer() }

It may also be marginally more efficient vs multiple appends, since the size of the array can be calculated ahead of time by map, vs append needing to resize the array multiple times as it grows.

Answer 2

Method 2 doesn't work because that initializer installs the exact same value in every index of the array.

You can use method one, or you can use a for loop:

var layers = [CALayer]()
layers.reserveCapacity(layerCount)

let layerCount = 10
for (_ in 1... layerCount)
{
  layers.append(CALayer())
}

(I'm still getting used to Swift so that syntax might not be perfect, but it should give you the general idea)